Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1897 insertions, 0 deletions

diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
new file mode 100644
index 000000000..eccbfb99e
--- /dev/null
+++ b/fs/xfs/xfs_log_cil.c
@@ -0,0 +1,1897 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2010 Red Hat, Inc. All Rights Reserved.
+ */
+
+#include "xfs.h"
+#include "xfs_fs.h"
+#include "xfs_format.h"
+#include "xfs_log_format.h"
+#include "xfs_shared.h"
+#include "xfs_trans_resv.h"
+#include "xfs_mount.h"
+#include "xfs_extent_busy.h"
+#include "xfs_trans.h"
+#include "xfs_trans_priv.h"
+#include "xfs_log.h"
+#include "xfs_log_priv.h"
+#include "xfs_trace.h"
+
+struct workqueue_struct *xfs_discard_wq;
+
+/*
+ * Allocate a new ticket. Failing to get a new ticket makes it really hard to
+ * recover, so we don't allow failure here. Also, we allocate in a context that
+ * we don't want to be issuing transactions from, so we need to tell the
+ * allocation code this as well.
+ *
+ * We don't reserve any space for the ticket - we are going to steal whatever
+ * space we require from transactions as they commit. To ensure we reserve all
+ * the space required, we need to set the current reservation of the ticket to
+ * zero so that we know to steal the initial transaction overhead from the
+ * first transaction commit.
+ */
+static struct xlog_ticket *
+xlog_cil_ticket_alloc(
+	struct xlog	*log)
+{
+	struct xlog_ticket *tic;
+
+	tic = xlog_ticket_alloc(log, 0, 1, 0);
+
+	/*
+	 * set the current reservation to zero so we know to steal the basic
+	 * transaction overhead reservation from the first transaction commit.
+	 */
+	tic->t_curr_res = 0;
+	tic->t_iclog_hdrs = 0;
+	return tic;
+}
+
+static inline void
+xlog_cil_set_iclog_hdr_count(struct xfs_cil *cil)
+{
+	struct xlog	*log = cil->xc_log;
+
+	atomic_set(&cil->xc_iclog_hdrs,
+		   (XLOG_CIL_BLOCKING_SPACE_LIMIT(log) /
+			(log->l_iclog_size - log->l_iclog_hsize)));
+}
+
+/*
+ * Check if the current log item was first committed in this sequence.
+ * We can't rely on just the log item being in the CIL, we have to check
+ * the recorded commit sequence number.
+ *
+ * Note: for this to be used in a non-racy manner, it has to be called with
+ * CIL flushing locked out. As a result, it should only be used during the
+ * transaction commit process when deciding what to format into the item.
+ */
+static bool
+xlog_item_in_current_chkpt(
+	struct xfs_cil		*cil,
+	struct xfs_log_item	*lip)
+{
+	if (test_bit(XLOG_CIL_EMPTY, &cil->xc_flags))
+		return false;
+
+	/*
+	 * li_seq is written on the first commit of a log item to record the
+	 * first checkpoint it is written to. Hence if it is different to the
+	 * current sequence, we're in a new checkpoint.
+	 */
+	return lip->li_seq == READ_ONCE(cil->xc_current_sequence);
+}
+
+bool
+xfs_log_item_in_current_chkpt(
+	struct xfs_log_item *lip)
+{
+	return xlog_item_in_current_chkpt(lip->li_log->l_cilp, lip);
+}
+
+/*
+ * Unavoidable forward declaration - xlog_cil_push_work() calls
+ * xlog_cil_ctx_alloc() itself.
+ */
+static void xlog_cil_push_work(struct work_struct *work);
+
+static struct xfs_cil_ctx *
+xlog_cil_ctx_alloc(void)
+{
+	struct xfs_cil_ctx	*ctx;
+
+	ctx = kmem_zalloc(sizeof(*ctx), KM_NOFS);
+	INIT_LIST_HEAD(&ctx->committing);
+	INIT_LIST_HEAD(&ctx->busy_extents);
+	INIT_LIST_HEAD(&ctx->log_items);
+	INIT_LIST_HEAD(&ctx->lv_chain);
+	INIT_WORK(&ctx->push_work, xlog_cil_push_work);
+	return ctx;
+}
+
+/*
+ * Aggregate the CIL per cpu structures into global counts, lists, etc and
+ * clear the percpu state ready for the next context to use. This is called
+ * from the push code with the context lock held exclusively, hence nothing else
+ * will be accessing or modifying the per-cpu counters.
+ */
+static void
+xlog_cil_push_pcp_aggregate(
+	struct xfs_cil		*cil,
+	struct xfs_cil_ctx	*ctx)
+{
+	struct xlog_cil_pcp	*cilpcp;
+	int			cpu;
+
+	for_each_online_cpu(cpu) {
+		cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
+
+		ctx->ticket->t_curr_res += cilpcp->space_reserved;
+		cilpcp->space_reserved = 0;
+
+		if (!list_empty(&cilpcp->busy_extents)) {
+			list_splice_init(&cilpcp->busy_extents,
+					&ctx->busy_extents);
+		}
+		if (!list_empty(&cilpcp->log_items))
+			list_splice_init(&cilpcp->log_items, &ctx->log_items);
+
+		/*
+		 * We're in the middle of switching cil contexts.  Reset the
+		 * counter we use to detect when the current context is nearing
+		 * full.
+		 */
+		cilpcp->space_used = 0;
+	}
+}
+
+/*
+ * Aggregate the CIL per-cpu space used counters into the global atomic value.
+ * This is called when the per-cpu counter aggregation will first pass the soft
+ * limit threshold so we can switch to atomic counter aggregation for accurate
+ * detection of hard limit traversal.
+ */
+static void
+xlog_cil_insert_pcp_aggregate(
+	struct xfs_cil		*cil,
+	struct xfs_cil_ctx	*ctx)
+{
+	struct xlog_cil_pcp	*cilpcp;
+	int			cpu;
+	int			count = 0;
+
+	/* Trigger atomic updates then aggregate only for the first caller */
+	if (!test_and_clear_bit(XLOG_CIL_PCP_SPACE, &cil->xc_flags))
+		return;
+
+	for_each_online_cpu(cpu) {
+		int	old, prev;
+
+		cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
+		do {
+			old = cilpcp->space_used;
+			prev = cmpxchg(&cilpcp->space_used, old, 0);
+		} while (old != prev);
+		count += old;
+	}
+	atomic_add(count, &ctx->space_used);
+}
+
+static void
+xlog_cil_ctx_switch(
+	struct xfs_cil		*cil,
+	struct xfs_cil_ctx	*ctx)
+{
+	xlog_cil_set_iclog_hdr_count(cil);
+	set_bit(XLOG_CIL_EMPTY, &cil->xc_flags);
+	set_bit(XLOG_CIL_PCP_SPACE, &cil->xc_flags);
+	ctx->sequence = ++cil->xc_current_sequence;
+	ctx->cil = cil;
+	cil->xc_ctx = ctx;
+}
+
+/*
+ * After the first stage of log recovery is done, we know where the head and
+ * tail of the log are. We need this log initialisation done before we can
+ * initialise the first CIL checkpoint context.
+ *
+ * Here we allocate a log ticket to track space usage during a CIL push.  This
+ * ticket is passed to xlog_write() directly so that we don't slowly leak log
+ * space by failing to account for space used by log headers and additional
+ * region headers for split regions.
+ */
+void
+xlog_cil_init_post_recovery(
+	struct xlog	*log)
+{
+	log->l_cilp->xc_ctx->ticket = xlog_cil_ticket_alloc(log);
+	log->l_cilp->xc_ctx->sequence = 1;
+	xlog_cil_set_iclog_hdr_count(log->l_cilp);
+}
+
+static inline int
+xlog_cil_iovec_space(
+	uint	niovecs)
+{
+	return round_up((sizeof(struct xfs_log_vec) +
+					niovecs * sizeof(struct xfs_log_iovec)),
+			sizeof(uint64_t));
+}
+
+/*
+ * Allocate or pin log vector buffers for CIL insertion.
+ *
+ * The CIL currently uses disposable buffers for copying a snapshot of the
+ * modified items into the log during a push. The biggest problem with this is
+ * the requirement to allocate the disposable buffer during the commit if:
+ *	a) does not exist; or
+ *	b) it is too small
+ *
+ * If we do this allocation within xlog_cil_insert_format_items(), it is done
+ * under the xc_ctx_lock, which means that a CIL push cannot occur during
+ * the memory allocation. This means that we have a potential deadlock situation
+ * under low memory conditions when we have lots of dirty metadata pinned in
+ * the CIL and we need a CIL commit to occur to free memory.
+ *
+ * To avoid this, we need to move the memory allocation outside the
+ * xc_ctx_lock, but because the log vector buffers are disposable, that opens
+ * up a TOCTOU race condition w.r.t. the CIL committing and removing the log
+ * vector buffers between the check and the formatting of the item into the
+ * log vector buffer within the xc_ctx_lock.
+ *
+ * Because the log vector buffer needs to be unchanged during the CIL push
+ * process, we cannot share the buffer between the transaction commit (which
+ * modifies the buffer) and the CIL push context that is writing the changes
+ * into the log. This means skipping preallocation of buffer space is
+ * unreliable, but we most definitely do not want to be allocating and freeing
+ * buffers unnecessarily during commits when overwrites can be done safely.
+ *
+ * The simplest solution to this problem is to allocate a shadow buffer when a
+ * log item is committed for the second time, and then to only use this buffer
+ * if necessary. The buffer can remain attached to the log item until such time
+ * it is needed, and this is the buffer that is reallocated to match the size of
+ * the incoming modification. Then during the formatting of the item we can swap
+ * the active buffer with the new one if we can't reuse the existing buffer. We
+ * don't free the old buffer as it may be reused on the next modification if
+ * it's size is right, otherwise we'll free and reallocate it at that point.
+ *
+ * This function builds a vector for the changes in each log item in the
+ * transaction. It then works out the length of the buffer needed for each log
+ * item, allocates them and attaches the vector to the log item in preparation
+ * for the formatting step which occurs under the xc_ctx_lock.
+ *
+ * While this means the memory footprint goes up, it avoids the repeated
+ * alloc/free pattern that repeated modifications of an item would otherwise
+ * cause, and hence minimises the CPU overhead of such behaviour.
+ */
+static void
+xlog_cil_alloc_shadow_bufs(
+	struct xlog		*log,
+	struct xfs_trans	*tp)
+{
+	struct xfs_log_item	*lip;
+
+	list_for_each_entry(lip, &tp->t_items, li_trans) {
+		struct xfs_log_vec *lv;
+		int	niovecs = 0;
+		int	nbytes = 0;
+		int	buf_size;
+		bool	ordered = false;
+
+		/* Skip items which aren't dirty in this transaction. */
+		if (!test_bit(XFS_LI_DIRTY, &lip->li_flags))
+			continue;
+
+		/* get number of vecs and size of data to be stored */
+		lip->li_ops->iop_size(lip, &niovecs, &nbytes);
+
+		/*
+		 * Ordered items need to be tracked but we do not wish to write
+		 * them. We need a logvec to track the object, but we do not
+		 * need an iovec or buffer to be allocated for copying data.
+		 */
+		if (niovecs == XFS_LOG_VEC_ORDERED) {
+			ordered = true;
+			niovecs = 0;
+			nbytes = 0;
+		}
+
+		/*
+		 * We 64-bit align the length of each iovec so that the start of
+		 * the next one is naturally aligned.  We'll need to account for
+		 * that slack space here.
+		 *
+		 * We also add the xlog_op_header to each region when
+		 * formatting, but that's not accounted to the size of the item
+		 * at this point. Hence we'll need an addition number of bytes
+		 * for each vector to hold an opheader.
+		 *
+		 * Then round nbytes up to 64-bit alignment so that the initial
+		 * buffer alignment is easy to calculate and verify.
+		 */
+		nbytes += niovecs *
+			(sizeof(uint64_t) + sizeof(struct xlog_op_header));
+		nbytes = round_up(nbytes, sizeof(uint64_t));
+
+		/*
+		 * The data buffer needs to start 64-bit aligned, so round up
+		 * that space to ensure we can align it appropriately and not
+		 * overrun the buffer.
+		 */
+		buf_size = nbytes + xlog_cil_iovec_space(niovecs);
+
+		/*
+		 * if we have no shadow buffer, or it is too small, we need to
+		 * reallocate it.
+		 */
+		if (!lip->li_lv_shadow ||
+		    buf_size > lip->li_lv_shadow->lv_size) {
+			/*
+			 * We free and allocate here as a realloc would copy
+			 * unnecessary data. We don't use kvzalloc() for the
+			 * same reason - we don't need to zero the data area in
+			 * the buffer, only the log vector header and the iovec
+			 * storage.
+			 */
+			kmem_free(lip->li_lv_shadow);
+			lv = xlog_kvmalloc(buf_size);
+
+			memset(lv, 0, xlog_cil_iovec_space(niovecs));
+
+			INIT_LIST_HEAD(&lv->lv_list);
+			lv->lv_item = lip;
+			lv->lv_size = buf_size;
+			if (ordered)
+				lv->lv_buf_len = XFS_LOG_VEC_ORDERED;
+			else
+				lv->lv_iovecp = (struct xfs_log_iovec *)&lv[1];
+			lip->li_lv_shadow = lv;
+		} else {
+			/* same or smaller, optimise common overwrite case */
+			lv = lip->li_lv_shadow;
+			if (ordered)
+				lv->lv_buf_len = XFS_LOG_VEC_ORDERED;
+			else
+				lv->lv_buf_len = 0;
+			lv->lv_bytes = 0;
+		}
+
+		/* Ensure the lv is set up according to ->iop_size */
+		lv->lv_niovecs = niovecs;
+
+		/* The allocated data region lies beyond the iovec region */
+		lv->lv_buf = (char *)lv + xlog_cil_iovec_space(niovecs);
+	}
+
+}
+
+/*
+ * Prepare the log item for insertion into the CIL. Calculate the difference in
+ * log space it will consume, and if it is a new item pin it as well.
+ */
+STATIC void
+xfs_cil_prepare_item(
+	struct xlog		*log,
+	struct xfs_log_vec	*lv,
+	struct xfs_log_vec	*old_lv,
+	int			*diff_len)
+{
+	/* Account for the new LV being passed in */
+	if (lv->lv_buf_len != XFS_LOG_VEC_ORDERED)
+		*diff_len += lv->lv_bytes;
+
+	/*
+	 * If there is no old LV, this is the first time we've seen the item in
+	 * this CIL context and so we need to pin it. If we are replacing the
+	 * old_lv, then remove the space it accounts for and make it the shadow
+	 * buffer for later freeing. In both cases we are now switching to the
+	 * shadow buffer, so update the pointer to it appropriately.
+	 */
+	if (!old_lv) {
+		if (lv->lv_item->li_ops->iop_pin)
+			lv->lv_item->li_ops->iop_pin(lv->lv_item);
+		lv->lv_item->li_lv_shadow = NULL;
+	} else if (old_lv != lv) {
+		ASSERT(lv->lv_buf_len != XFS_LOG_VEC_ORDERED);
+
+		*diff_len -= old_lv->lv_bytes;
+		lv->lv_item->li_lv_shadow = old_lv;
+	}
+
+	/* attach new log vector to log item */
+	lv->lv_item->li_lv = lv;
+
+	/*
+	 * If this is the first time the item is being committed to the
+	 * CIL, store the sequence number on the log item so we can
+	 * tell in future commits whether this is the first checkpoint
+	 * the item is being committed into.
+	 */
+	if (!lv->lv_item->li_seq)
+		lv->lv_item->li_seq = log->l_cilp->xc_ctx->sequence;
+}
+
+/*
+ * Format log item into a flat buffers
+ *
+ * For delayed logging, we need to hold a formatted buffer containing all the
+ * changes on the log item. This enables us to relog the item in memory and
+ * write it out asynchronously without needing to relock the object that was
+ * modified at the time it gets written into the iclog.
+ *
+ * This function takes the prepared log vectors attached to each log item, and
+ * formats the changes into the log vector buffer. The buffer it uses is
+ * dependent on the current state of the vector in the CIL - the shadow lv is
+ * guaranteed to be large enough for the current modification, but we will only
+ * use that if we can't reuse the existing lv. If we can't reuse the existing
+ * lv, then simple swap it out for the shadow lv. We don't free it - that is
+ * done lazily either by th enext modification or the freeing of the log item.
+ *
+ * We don't set up region headers during this process; we simply copy the
+ * regions into the flat buffer. We can do this because we still have to do a
+ * formatting step to write the regions into the iclog buffer.  Writing the
+ * ophdrs during the iclog write means that we can support splitting large
+ * regions across iclog boundares without needing a change in the format of the
+ * item/region encapsulation.
+ *
+ * Hence what we need to do now is change the rewrite the vector array to point
+ * to the copied region inside the buffer we just allocated. This allows us to
+ * format the regions into the iclog as though they are being formatted
+ * directly out of the objects themselves.
+ */
+static void
+xlog_cil_insert_format_items(
+	struct xlog		*log,
+	struct xfs_trans	*tp,
+	int			*diff_len)
+{
+	struct xfs_log_item	*lip;
+
+	/* Bail out if we didn't find a log item.  */
+	if (list_empty(&tp->t_items)) {
+		ASSERT(0);
+		return;
+	}
+
+	list_for_each_entry(lip, &tp->t_items, li_trans) {
+		struct xfs_log_vec *lv;
+		struct xfs_log_vec *old_lv = NULL;
+		struct xfs_log_vec *shadow;
+		bool	ordered = false;
+
+		/* Skip items which aren't dirty in this transaction. */
+		if (!test_bit(XFS_LI_DIRTY, &lip->li_flags))
+			continue;
+
+		/*
+		 * The formatting size information is already attached to
+		 * the shadow lv on the log item.
+		 */
+		shadow = lip->li_lv_shadow;
+		if (shadow->lv_buf_len == XFS_LOG_VEC_ORDERED)
+			ordered = true;
+
+		/* Skip items that do not have any vectors for writing */
+		if (!shadow->lv_niovecs && !ordered)
+			continue;
+
+		/* compare to existing item size */
+		old_lv = lip->li_lv;
+		if (lip->li_lv && shadow->lv_size <= lip->li_lv->lv_size) {
+			/* same or smaller, optimise common overwrite case */
+			lv = lip->li_lv;
+
+			if (ordered)
+				goto insert;
+
+			/*
+			 * set the item up as though it is a new insertion so
+			 * that the space reservation accounting is correct.
+			 */
+			*diff_len -= lv->lv_bytes;
+
+			/* Ensure the lv is set up according to ->iop_size */
+			lv->lv_niovecs = shadow->lv_niovecs;
+
+			/* reset the lv buffer information for new formatting */
+			lv->lv_buf_len = 0;
+			lv->lv_bytes = 0;
+			lv->lv_buf = (char *)lv +
+					xlog_cil_iovec_space(lv->lv_niovecs);
+		} else {
+			/* switch to shadow buffer! */
+			lv = shadow;
+			lv->lv_item = lip;
+			if (ordered) {
+				/* track as an ordered logvec */
+				ASSERT(lip->li_lv == NULL);
+				goto insert;
+			}
+		}
+
+		ASSERT(IS_ALIGNED((unsigned long)lv->lv_buf, sizeof(uint64_t)));
+		lip->li_ops->iop_format(lip, lv);
+insert:
+		xfs_cil_prepare_item(log, lv, old_lv, diff_len);
+	}
+}
+
+/*
+ * The use of lockless waitqueue_active() requires that the caller has
+ * serialised itself against the wakeup call in xlog_cil_push_work(). That
+ * can be done by either holding the push lock or the context lock.
+ */
+static inline bool
+xlog_cil_over_hard_limit(
+	struct xlog	*log,
+	int32_t		space_used)
+{
+	if (waitqueue_active(&log->l_cilp->xc_push_wait))
+		return true;
+	if (space_used >= XLOG_CIL_BLOCKING_SPACE_LIMIT(log))
+		return true;
+	return false;
+}
+
+/*
+ * Insert the log items into the CIL and calculate the difference in space
+ * consumed by the item. Add the space to the checkpoint ticket and calculate
+ * if the change requires additional log metadata. If it does, take that space
+ * as well. Remove the amount of space we added to the checkpoint ticket from
+ * the current transaction ticket so that the accounting works out correctly.
+ */
+static void
+xlog_cil_insert_items(
+	struct xlog		*log,
+	struct xfs_trans	*tp,
+	uint32_t		released_space)
+{
+	struct xfs_cil		*cil = log->l_cilp;
+	struct xfs_cil_ctx	*ctx = cil->xc_ctx;
+	struct xfs_log_item	*lip;
+	int			len = 0;
+	int			iovhdr_res = 0, split_res = 0, ctx_res = 0;
+	int			space_used;
+	int			order;
+	struct xlog_cil_pcp	*cilpcp;
+
+	ASSERT(tp);
+
+	/*
+	 * We can do this safely because the context can't checkpoint until we
+	 * are done so it doesn't matter exactly how we update the CIL.
+	 */
+	xlog_cil_insert_format_items(log, tp, &len);
+
+	/*
+	 * Subtract the space released by intent cancelation from the space we
+	 * consumed so that we remove it from the CIL space and add it back to
+	 * the current transaction reservation context.
+	 */
+	len -= released_space;
+
+	/*
+	 * Grab the per-cpu pointer for the CIL before we start any accounting.
+	 * That ensures that we are running with pre-emption disabled and so we
+	 * can't be scheduled away between split sample/update operations that
+	 * are done without outside locking to serialise them.
+	 */
+	cilpcp = get_cpu_ptr(cil->xc_pcp);
+
+	/*
+	 * We need to take the CIL checkpoint unit reservation on the first
+	 * commit into the CIL. Test the XLOG_CIL_EMPTY bit first so we don't
+	 * unnecessarily do an atomic op in the fast path here. We can clear the
+	 * XLOG_CIL_EMPTY bit as we are under the xc_ctx_lock here and that
+	 * needs to be held exclusively to reset the XLOG_CIL_EMPTY bit.
+	 */
+	if (test_bit(XLOG_CIL_EMPTY, &cil->xc_flags) &&
+	    test_and_clear_bit(XLOG_CIL_EMPTY, &cil->xc_flags))
+		ctx_res = ctx->ticket->t_unit_res;
+
+	/*
+	 * Check if we need to steal iclog headers. atomic_read() is not a
+	 * locked atomic operation, so we can check the value before we do any
+	 * real atomic ops in the fast path. If we've already taken the CIL unit
+	 * reservation from this commit, we've already got one iclog header
+	 * space reserved so we have to account for that otherwise we risk
+	 * overrunning the reservation on this ticket.
+	 *
+	 * If the CIL is already at the hard limit, we might need more header
+	 * space that originally reserved. So steal more header space from every
+	 * commit that occurs once we are over the hard limit to ensure the CIL
+	 * push won't run out of reservation space.
+	 *
+	 * This can steal more than we need, but that's OK.
+	 *
+	 * The cil->xc_ctx_lock provides the serialisation necessary for safely
+	 * calling xlog_cil_over_hard_limit() in this context.
+	 */
+	space_used = atomic_read(&ctx->space_used) + cilpcp->space_used + len;
+	if (atomic_read(&cil->xc_iclog_hdrs) > 0 ||
+	    xlog_cil_over_hard_limit(log, space_used)) {
+		split_res = log->l_iclog_hsize +
+					sizeof(struct xlog_op_header);
+		if (ctx_res)
+			ctx_res += split_res * (tp->t_ticket->t_iclog_hdrs - 1);
+		else
+			ctx_res = split_res * tp->t_ticket->t_iclog_hdrs;
+		atomic_sub(tp->t_ticket->t_iclog_hdrs, &cil->xc_iclog_hdrs);
+	}
+	cilpcp->space_reserved += ctx_res;
+
+	/*
+	 * Accurately account when over the soft limit, otherwise fold the
+	 * percpu count into the global count if over the per-cpu threshold.
+	 */
+	if (!test_bit(XLOG_CIL_PCP_SPACE, &cil->xc_flags)) {
+		atomic_add(len, &ctx->space_used);
+	} else if (cilpcp->space_used + len >
+			(XLOG_CIL_SPACE_LIMIT(log) / num_online_cpus())) {
+		space_used = atomic_add_return(cilpcp->space_used + len,
+						&ctx->space_used);
+		cilpcp->space_used = 0;
+
+		/*
+		 * If we just transitioned over the soft limit, we need to
+		 * transition to the global atomic counter.
+		 */
+		if (space_used >= XLOG_CIL_SPACE_LIMIT(log))
+			xlog_cil_insert_pcp_aggregate(cil, ctx);
+	} else {
+		cilpcp->space_used += len;
+	}
+	/* attach the transaction to the CIL if it has any busy extents */
+	if (!list_empty(&tp->t_busy))
+		list_splice_init(&tp->t_busy, &cilpcp->busy_extents);
+
+	/*
+	 * Now update the order of everything modified in the transaction
+	 * and insert items into the CIL if they aren't already there.
+	 * We do this here so we only need to take the CIL lock once during
+	 * the transaction commit.
+	 */
+	order = atomic_inc_return(&ctx->order_id);
+	list_for_each_entry(lip, &tp->t_items, li_trans) {
+		/* Skip items which aren't dirty in this transaction. */
+		if (!test_bit(XFS_LI_DIRTY, &lip->li_flags))
+			continue;
+
+		lip->li_order_id = order;
+		if (!list_empty(&lip->li_cil))
+			continue;
+		list_add_tail(&lip->li_cil, &cilpcp->log_items);
+	}
+	put_cpu_ptr(cilpcp);
+
+	/*
+	 * If we've overrun the reservation, dump the tx details before we move
+	 * the log items. Shutdown is imminent...
+	 */
+	tp->t_ticket->t_curr_res -= ctx_res + len;
+	if (WARN_ON(tp->t_ticket->t_curr_res < 0)) {
+		xfs_warn(log->l_mp, "Transaction log reservation overrun:");
+		xfs_warn(log->l_mp,
+			 "  log items: %d bytes (iov hdrs: %d bytes)",
+			 len, iovhdr_res);
+		xfs_warn(log->l_mp, "  split region headers: %d bytes",
+			 split_res);
+		xfs_warn(log->l_mp, "  ctx ticket: %d bytes", ctx_res);
+		xlog_print_trans(tp);
+		xlog_force_shutdown(log, SHUTDOWN_LOG_IO_ERROR);
+	}
+}
+
+static void
+xlog_cil_free_logvec(
+	struct list_head	*lv_chain)
+{
+	struct xfs_log_vec	*lv;
+
+	while (!list_empty(lv_chain)) {
+		lv = list_first_entry(lv_chain, struct xfs_log_vec, lv_list);
+		list_del_init(&lv->lv_list);
+		kmem_free(lv);
+	}
+}
+
+static void
+xlog_discard_endio_work(
+	struct work_struct	*work)
+{
+	struct xfs_cil_ctx	*ctx =
+		container_of(work, struct xfs_cil_ctx, discard_endio_work);
+	struct xfs_mount	*mp = ctx->cil->xc_log->l_mp;
+
+	xfs_extent_busy_clear(mp, &ctx->busy_extents, false);
+	kmem_free(ctx);
+}
+
+/*
+ * Queue up the actual completion to a thread to avoid IRQ-safe locking for
+ * pagb_lock.  Note that we need a unbounded workqueue, otherwise we might
+ * get the execution delayed up to 30 seconds for weird reasons.
+ */
+static void
+xlog_discard_endio(
+	struct bio		*bio)
+{
+	struct xfs_cil_ctx	*ctx = bio->bi_private;
+
+	INIT_WORK(&ctx->discard_endio_work, xlog_discard_endio_work);
+	queue_work(xfs_discard_wq, &ctx->discard_endio_work);
+	bio_put(bio);
+}
+
+static void
+xlog_discard_busy_extents(
+	struct xfs_mount	*mp,
+	struct xfs_cil_ctx	*ctx)
+{
+	struct list_head	*list = &ctx->busy_extents;
+	struct xfs_extent_busy	*busyp;
+	struct bio		*bio = NULL;
+	struct blk_plug		plug;
+	int			error = 0;
+
+	ASSERT(xfs_has_discard(mp));
+
+	blk_start_plug(&plug);
+	list_for_each_entry(busyp, list, list) {
+		trace_xfs_discard_extent(mp, busyp->agno, busyp->bno,
+					 busyp->length);
+
+		error = __blkdev_issue_discard(mp->m_ddev_targp->bt_bdev,
+				XFS_AGB_TO_DADDR(mp, busyp->agno, busyp->bno),
+				XFS_FSB_TO_BB(mp, busyp->length),
+				GFP_NOFS, &bio);
+		if (error && error != -EOPNOTSUPP) {
+			xfs_info(mp,
+	 "discard failed for extent [0x%llx,%u], error %d",
+				 (unsigned long long)busyp->bno,
+				 busyp->length,
+				 error);
+			break;
+		}
+	}
+
+	if (bio) {
+		bio->bi_private = ctx;
+		bio->bi_end_io = xlog_discard_endio;
+		submit_bio(bio);
+	} else {
+		xlog_discard_endio_work(&ctx->discard_endio_work);
+	}
+	blk_finish_plug(&plug);
+}
+
+/*
+ * Mark all items committed and clear busy extents. We free the log vector
+ * chains in a separate pass so that we unpin the log items as quickly as
+ * possible.
+ */
+static void
+xlog_cil_committed(
+	struct xfs_cil_ctx	*ctx)
+{
+	struct xfs_mount	*mp = ctx->cil->xc_log->l_mp;
+	bool			abort = xlog_is_shutdown(ctx->cil->xc_log);
+
+	/*
+	 * If the I/O failed, we're aborting the commit and already shutdown.
+	 * Wake any commit waiters before aborting the log items so we don't
+	 * block async log pushers on callbacks. Async log pushers explicitly do
+	 * not wait on log force completion because they may be holding locks
+	 * required to unpin items.
+	 */
+	if (abort) {
+		spin_lock(&ctx->cil->xc_push_lock);
+		wake_up_all(&ctx->cil->xc_start_wait);
+		wake_up_all(&ctx->cil->xc_commit_wait);
+		spin_unlock(&ctx->cil->xc_push_lock);
+	}
+
+	xfs_trans_committed_bulk(ctx->cil->xc_log->l_ailp, &ctx->lv_chain,
+					ctx->start_lsn, abort);
+
+	xfs_extent_busy_sort(&ctx->busy_extents);
+	xfs_extent_busy_clear(mp, &ctx->busy_extents,
+			      xfs_has_discard(mp) && !abort);
+
+	spin_lock(&ctx->cil->xc_push_lock);
+	list_del(&ctx->committing);
+	spin_unlock(&ctx->cil->xc_push_lock);
+
+	xlog_cil_free_logvec(&ctx->lv_chain);
+
+	if (!list_empty(&ctx->busy_extents))
+		xlog_discard_busy_extents(mp, ctx);
+	else
+		kmem_free(ctx);
+}
+
+void
+xlog_cil_process_committed(
+	struct list_head	*list)
+{
+	struct xfs_cil_ctx	*ctx;
+
+	while ((ctx = list_first_entry_or_null(list,
+			struct xfs_cil_ctx, iclog_entry))) {
+		list_del(&ctx->iclog_entry);
+		xlog_cil_committed(ctx);
+	}
+}
+
+/*
+* Record the LSN of the iclog we were just granted space to start writing into.
+* If the context doesn't have a start_lsn recorded, then this iclog will
+* contain the start record for the checkpoint. Otherwise this write contains
+* the commit record for the checkpoint.
+*/
+void
+xlog_cil_set_ctx_write_state(
+	struct xfs_cil_ctx	*ctx,
+	struct xlog_in_core	*iclog)
+{
+	struct xfs_cil		*cil = ctx->cil;
+	xfs_lsn_t		lsn = be64_to_cpu(iclog->ic_header.h_lsn);
+
+	ASSERT(!ctx->commit_lsn);
+	if (!ctx->start_lsn) {
+		spin_lock(&cil->xc_push_lock);
+		/*
+		 * The LSN we need to pass to the log items on transaction
+		 * commit is the LSN reported by the first log vector write, not
+		 * the commit lsn. If we use the commit record lsn then we can
+		 * move the grant write head beyond the tail LSN and overwrite
+		 * it.
+		 */
+		ctx->start_lsn = lsn;
+		wake_up_all(&cil->xc_start_wait);
+		spin_unlock(&cil->xc_push_lock);
+
+		/*
+		 * Make sure the metadata we are about to overwrite in the log
+		 * has been flushed to stable storage before this iclog is
+		 * issued.
+		 */
+		spin_lock(&cil->xc_log->l_icloglock);
+		iclog->ic_flags |= XLOG_ICL_NEED_FLUSH;
+		spin_unlock(&cil->xc_log->l_icloglock);
+		return;
+	}
+
+	/*
+	 * Take a reference to the iclog for the context so that we still hold
+	 * it when xlog_write is done and has released it. This means the
+	 * context controls when the iclog is released for IO.
+	 */
+	atomic_inc(&iclog->ic_refcnt);
+
+	/*
+	 * xlog_state_get_iclog_space() guarantees there is enough space in the
+	 * iclog for an entire commit record, so we can attach the context
+	 * callbacks now.  This needs to be done before we make the commit_lsn
+	 * visible to waiters so that checkpoints with commit records in the
+	 * same iclog order their IO completion callbacks in the same order that
+	 * the commit records appear in the iclog.
+	 */
+	spin_lock(&cil->xc_log->l_icloglock);
+	list_add_tail(&ctx->iclog_entry, &iclog->ic_callbacks);
+	spin_unlock(&cil->xc_log->l_icloglock);
+
+	/*
+	 * Now we can record the commit LSN and wake anyone waiting for this
+	 * sequence to have the ordered commit record assigned to a physical
+	 * location in the log.
+	 */
+	spin_lock(&cil->xc_push_lock);
+	ctx->commit_iclog = iclog;
+	ctx->commit_lsn = lsn;
+	wake_up_all(&cil->xc_commit_wait);
+	spin_unlock(&cil->xc_push_lock);
+}
+
+
+/*
+ * Ensure that the order of log writes follows checkpoint sequence order. This
+ * relies on the context LSN being zero until the log write has guaranteed the
+ * LSN that the log write will start at via xlog_state_get_iclog_space().
+ */
+enum _record_type {
+	_START_RECORD,
+	_COMMIT_RECORD,
+};
+
+static int
+xlog_cil_order_write(
+	struct xfs_cil		*cil,
+	xfs_csn_t		sequence,
+	enum _record_type	record)
+{
+	struct xfs_cil_ctx	*ctx;
+
+restart:
+	spin_lock(&cil->xc_push_lock);
+	list_for_each_entry(ctx, &cil->xc_committing, committing) {
+		/*
+		 * Avoid getting stuck in this loop because we were woken by the
+		 * shutdown, but then went back to sleep once already in the
+		 * shutdown state.
+		 */
+		if (xlog_is_shutdown(cil->xc_log)) {
+			spin_unlock(&cil->xc_push_lock);
+			return -EIO;
+		}
+
+		/*
+		 * Higher sequences will wait for this one so skip them.
+		 * Don't wait for our own sequence, either.
+		 */
+		if (ctx->sequence >= sequence)
+			continue;
+
+		/* Wait until the LSN for the record has been recorded. */
+		switch (record) {
+		case _START_RECORD:
+			if (!ctx->start_lsn) {
+				xlog_wait(&cil->xc_start_wait, &cil->xc_push_lock);
+				goto restart;
+			}
+			break;
+		case _COMMIT_RECORD:
+			if (!ctx->commit_lsn) {
+				xlog_wait(&cil->xc_commit_wait, &cil->xc_push_lock);
+				goto restart;
+			}
+			break;
+		}
+	}
+	spin_unlock(&cil->xc_push_lock);
+	return 0;
+}
+
+/*
+ * Write out the log vector change now attached to the CIL context. This will
+ * write a start record that needs to be strictly ordered in ascending CIL
+ * sequence order so that log recovery will always use in-order start LSNs when
+ * replaying checkpoints.
+ */
+static int
+xlog_cil_write_chain(
+	struct xfs_cil_ctx	*ctx,
+	uint32_t		chain_len)
+{
+	struct xlog		*log = ctx->cil->xc_log;
+	int			error;
+
+	error = xlog_cil_order_write(ctx->cil, ctx->sequence, _START_RECORD);
+	if (error)
+		return error;
+	return xlog_write(log, ctx, &ctx->lv_chain, ctx->ticket, chain_len);
+}
+
+/*
+ * Write out the commit record of a checkpoint transaction to close off a
+ * running log write. These commit records are strictly ordered in ascending CIL
+ * sequence order so that log recovery will always replay the checkpoints in the
+ * correct order.
+ */
+static int
+xlog_cil_write_commit_record(
+	struct xfs_cil_ctx	*ctx)
+{
+	struct xlog		*log = ctx->cil->xc_log;
+	struct xlog_op_header	ophdr = {
+		.oh_clientid = XFS_TRANSACTION,
+		.oh_tid = cpu_to_be32(ctx->ticket->t_tid),
+		.oh_flags = XLOG_COMMIT_TRANS,
+	};
+	struct xfs_log_iovec	reg = {
+		.i_addr = &ophdr,
+		.i_len = sizeof(struct xlog_op_header),
+		.i_type = XLOG_REG_TYPE_COMMIT,
+	};
+	struct xfs_log_vec	vec = {
+		.lv_niovecs = 1,
+		.lv_iovecp = &reg,
+	};
+	int			error;
+	LIST_HEAD(lv_chain);
+	list_add(&vec.lv_list, &lv_chain);
+
+	if (xlog_is_shutdown(log))
+		return -EIO;
+
+	error = xlog_cil_order_write(ctx->cil, ctx->sequence, _COMMIT_RECORD);
+	if (error)
+		return error;
+
+	/* account for space used by record data */
+	ctx->ticket->t_curr_res -= reg.i_len;
+	error = xlog_write(log, ctx, &lv_chain, ctx->ticket, reg.i_len);
+	if (error)
+		xlog_force_shutdown(log, SHUTDOWN_LOG_IO_ERROR);
+	return error;
+}
+
+struct xlog_cil_trans_hdr {
+	struct xlog_op_header	oph[2];
+	struct xfs_trans_header	thdr;
+	struct xfs_log_iovec	lhdr[2];
+};
+
+/*
+ * Build a checkpoint transaction header to begin the journal transaction.  We
+ * need to account for the space used by the transaction header here as it is
+ * not accounted for in xlog_write().
+ *
+ * This is the only place we write a transaction header, so we also build the
+ * log opheaders that indicate the start of a log transaction and wrap the
+ * transaction header. We keep the start record in it's own log vector rather
+ * than compacting them into a single region as this ends up making the logic
+ * in xlog_write() for handling empty opheaders for start, commit and unmount
+ * records much simpler.
+ */
+static void
+xlog_cil_build_trans_hdr(
+	struct xfs_cil_ctx	*ctx,
+	struct xlog_cil_trans_hdr *hdr,
+	struct xfs_log_vec	*lvhdr,
+	int			num_iovecs)
+{
+	struct xlog_ticket	*tic = ctx->ticket;
+	__be32			tid = cpu_to_be32(tic->t_tid);
+
+	memset(hdr, 0, sizeof(*hdr));
+
+	/* Log start record */
+	hdr->oph[0].oh_tid = tid;
+	hdr->oph[0].oh_clientid = XFS_TRANSACTION;
+	hdr->oph[0].oh_flags = XLOG_START_TRANS;
+
+	/* log iovec region pointer */
+	hdr->lhdr[0].i_addr = &hdr->oph[0];
+	hdr->lhdr[0].i_len = sizeof(struct xlog_op_header);
+	hdr->lhdr[0].i_type = XLOG_REG_TYPE_LRHEADER;
+
+	/* log opheader */
+	hdr->oph[1].oh_tid = tid;
+	hdr->oph[1].oh_clientid = XFS_TRANSACTION;
+	hdr->oph[1].oh_len = cpu_to_be32(sizeof(struct xfs_trans_header));
+
+	/* transaction header in host byte order format */
+	hdr->thdr.th_magic = XFS_TRANS_HEADER_MAGIC;
+	hdr->thdr.th_type = XFS_TRANS_CHECKPOINT;
+	hdr->thdr.th_tid = tic->t_tid;
+	hdr->thdr.th_num_items = num_iovecs;
+
+	/* log iovec region pointer */
+	hdr->lhdr[1].i_addr = &hdr->oph[1];
+	hdr->lhdr[1].i_len = sizeof(struct xlog_op_header) +
+				sizeof(struct xfs_trans_header);
+	hdr->lhdr[1].i_type = XLOG_REG_TYPE_TRANSHDR;
+
+	lvhdr->lv_niovecs = 2;
+	lvhdr->lv_iovecp = &hdr->lhdr[0];
+	lvhdr->lv_bytes = hdr->lhdr[0].i_len + hdr->lhdr[1].i_len;
+
+	tic->t_curr_res -= lvhdr->lv_bytes;
+}
+
+/*
+ * CIL item reordering compare function. We want to order in ascending ID order,
+ * but we want to leave items with the same ID in the order they were added to
+ * the list. This is important for operations like reflink where we log 4 order
+ * dependent intents in a single transaction when we overwrite an existing
+ * shared extent with a new shared extent. i.e. BUI(unmap), CUI(drop),
+ * CUI (inc), BUI(remap)...
+ */
+static int
+xlog_cil_order_cmp(
+	void			*priv,
+	const struct list_head	*a,
+	const struct list_head	*b)
+{
+	struct xfs_log_vec	*l1 = container_of(a, struct xfs_log_vec, lv_list);
+	struct xfs_log_vec	*l2 = container_of(b, struct xfs_log_vec, lv_list);
+
+	return l1->lv_order_id > l2->lv_order_id;
+}
+
+/*
+ * Pull all the log vectors off the items in the CIL, and remove the items from
+ * the CIL. We don't need the CIL lock here because it's only needed on the
+ * transaction commit side which is currently locked out by the flush lock.
+ *
+ * If a log item is marked with a whiteout, we do not need to write it to the
+ * journal and so we just move them to the whiteout list for the caller to
+ * dispose of appropriately.
+ */
+static void
+xlog_cil_build_lv_chain(
+	struct xfs_cil_ctx	*ctx,
+	struct list_head	*whiteouts,
+	uint32_t		*num_iovecs,
+	uint32_t		*num_bytes)
+{
+	while (!list_empty(&ctx->log_items)) {
+		struct xfs_log_item	*item;
+		struct xfs_log_vec	*lv;
+
+		item = list_first_entry(&ctx->log_items,
+					struct xfs_log_item, li_cil);
+
+		if (test_bit(XFS_LI_WHITEOUT, &item->li_flags)) {
+			list_move(&item->li_cil, whiteouts);
+			trace_xfs_cil_whiteout_skip(item);
+			continue;
+		}
+
+		lv = item->li_lv;
+		lv->lv_order_id = item->li_order_id;
+
+		/* we don't write ordered log vectors */
+		if (lv->lv_buf_len != XFS_LOG_VEC_ORDERED)
+			*num_bytes += lv->lv_bytes;
+		*num_iovecs += lv->lv_niovecs;
+		list_add_tail(&lv->lv_list, &ctx->lv_chain);
+
+		list_del_init(&item->li_cil);
+		item->li_order_id = 0;
+		item->li_lv = NULL;
+	}
+}
+
+static void
+xlog_cil_cleanup_whiteouts(
+	struct list_head	*whiteouts)
+{
+	while (!list_empty(whiteouts)) {
+		struct xfs_log_item *item = list_first_entry(whiteouts,
+						struct xfs_log_item, li_cil);
+		list_del_init(&item->li_cil);
+		trace_xfs_cil_whiteout_unpin(item);
+		item->li_ops->iop_unpin(item, 1);
+	}
+}
+
+/*
+ * Push the Committed Item List to the log.
+ *
+ * If the current sequence is the same as xc_push_seq we need to do a flush. If
+ * xc_push_seq is less than the current sequence, then it has already been
+ * flushed and we don't need to do anything - the caller will wait for it to
+ * complete if necessary.
+ *
+ * xc_push_seq is checked unlocked against the sequence number for a match.
+ * Hence we can allow log forces to run racily and not issue pushes for the
+ * same sequence twice.  If we get a race between multiple pushes for the same
+ * sequence they will block on the first one and then abort, hence avoiding
+ * needless pushes.
+ */
+static void
+xlog_cil_push_work(
+	struct work_struct	*work)
+{
+	struct xfs_cil_ctx	*ctx =
+		container_of(work, struct xfs_cil_ctx, push_work);
+	struct xfs_cil		*cil = ctx->cil;
+	struct xlog		*log = cil->xc_log;
+	struct xfs_cil_ctx	*new_ctx;
+	int			num_iovecs = 0;
+	int			num_bytes = 0;
+	int			error = 0;
+	struct xlog_cil_trans_hdr thdr;
+	struct xfs_log_vec	lvhdr = {};
+	xfs_csn_t		push_seq;
+	bool			push_commit_stable;
+	LIST_HEAD		(whiteouts);
+	struct xlog_ticket	*ticket;
+
+	new_ctx = xlog_cil_ctx_alloc();
+	new_ctx->ticket = xlog_cil_ticket_alloc(log);
+
+	down_write(&cil->xc_ctx_lock);
+
+	spin_lock(&cil->xc_push_lock);
+	push_seq = cil->xc_push_seq;
+	ASSERT(push_seq <= ctx->sequence);
+	push_commit_stable = cil->xc_push_commit_stable;
+	cil->xc_push_commit_stable = false;
+
+	/*
+	 * As we are about to switch to a new, empty CIL context, we no longer
+	 * need to throttle tasks on CIL space overruns. Wake any waiters that
+	 * the hard push throttle may have caught so they can start committing
+	 * to the new context. The ctx->xc_push_lock provides the serialisation
+	 * necessary for safely using the lockless waitqueue_active() check in
+	 * this context.
+	 */
+	if (waitqueue_active(&cil->xc_push_wait))
+		wake_up_all(&cil->xc_push_wait);
+
+	xlog_cil_push_pcp_aggregate(cil, ctx);
+
+	/*
+	 * Check if we've anything to push. If there is nothing, then we don't
+	 * move on to a new sequence number and so we have to be able to push
+	 * this sequence again later.
+	 */
+	if (test_bit(XLOG_CIL_EMPTY, &cil->xc_flags)) {
+		cil->xc_push_seq = 0;
+		spin_unlock(&cil->xc_push_lock);
+		goto out_skip;
+	}
+
+
+	/* check for a previously pushed sequence */
+	if (push_seq < ctx->sequence) {
+		spin_unlock(&cil->xc_push_lock);
+		goto out_skip;
+	}
+
+	/*
+	 * We are now going to push this context, so add it to the committing
+	 * list before we do anything else. This ensures that anyone waiting on
+	 * this push can easily detect the difference between a "push in
+	 * progress" and "CIL is empty, nothing to do".
+	 *
+	 * IOWs, a wait loop can now check for:
+	 *	the current sequence not being found on the committing list;
+	 *	an empty CIL; and
+	 *	an unchanged sequence number
+	 * to detect a push that had nothing to do and therefore does not need
+	 * waiting on. If the CIL is not empty, we get put on the committing
+	 * list before emptying the CIL and bumping the sequence number. Hence
+	 * an empty CIL and an unchanged sequence number means we jumped out
+	 * above after doing nothing.
+	 *
+	 * Hence the waiter will either find the commit sequence on the
+	 * committing list or the sequence number will be unchanged and the CIL
+	 * still dirty. In that latter case, the push has not yet started, and
+	 * so the waiter will have to continue trying to check the CIL
+	 * committing list until it is found. In extreme cases of delay, the
+	 * sequence may fully commit between the attempts the wait makes to wait
+	 * on the commit sequence.
+	 */
+	list_add(&ctx->committing, &cil->xc_committing);
+	spin_unlock(&cil->xc_push_lock);
+
+	xlog_cil_build_lv_chain(ctx, &whiteouts, &num_iovecs, &num_bytes);
+
+	/*
+	 * Switch the contexts so we can drop the context lock and move out
+	 * of a shared context. We can't just go straight to the commit record,
+	 * though - we need to synchronise with previous and future commits so
+	 * that the commit records are correctly ordered in the log to ensure
+	 * that we process items during log IO completion in the correct order.
+	 *
+	 * For example, if we get an EFI in one checkpoint and the EFD in the
+	 * next (e.g. due to log forces), we do not want the checkpoint with
+	 * the EFD to be committed before the checkpoint with the EFI.  Hence
+	 * we must strictly order the commit records of the checkpoints so
+	 * that: a) the checkpoint callbacks are attached to the iclogs in the
+	 * correct order; and b) the checkpoints are replayed in correct order
+	 * in log recovery.
+	 *
+	 * Hence we need to add this context to the committing context list so
+	 * that higher sequences will wait for us to write out a commit record
+	 * before they do.
+	 *
+	 * xfs_log_force_seq requires us to mirror the new sequence into the cil
+	 * structure atomically with the addition of this sequence to the
+	 * committing list. This also ensures that we can do unlocked checks
+	 * against the current sequence in log forces without risking
+	 * deferencing a freed context pointer.
+	 */
+	spin_lock(&cil->xc_push_lock);
+	xlog_cil_ctx_switch(cil, new_ctx);
+	spin_unlock(&cil->xc_push_lock);
+	up_write(&cil->xc_ctx_lock);
+
+	/*
+	 * Sort the log vector chain before we add the transaction headers.
+	 * This ensures we always have the transaction headers at the start
+	 * of the chain.
+	 */
+	list_sort(NULL, &ctx->lv_chain, xlog_cil_order_cmp);
+
+	/*
+	 * Build a checkpoint transaction header and write it to the log to
+	 * begin the transaction. We need to account for the space used by the
+	 * transaction header here as it is not accounted for in xlog_write().
+	 * Add the lvhdr to the head of the lv chain we pass to xlog_write() so
+	 * it gets written into the iclog first.
+	 */
+	xlog_cil_build_trans_hdr(ctx, &thdr, &lvhdr, num_iovecs);
+	num_bytes += lvhdr.lv_bytes;
+	list_add(&lvhdr.lv_list, &ctx->lv_chain);
+
+	/*
+	 * Take the lvhdr back off the lv_chain immediately after calling
+	 * xlog_cil_write_chain() as it should not be passed to log IO
+	 * completion.
+	 */
+	error = xlog_cil_write_chain(ctx, num_bytes);
+	list_del(&lvhdr.lv_list);
+	if (error)
+		goto out_abort_free_ticket;
+
+	error = xlog_cil_write_commit_record(ctx);
+	if (error)
+		goto out_abort_free_ticket;
+
+	/*
+	 * Grab the ticket from the ctx so we can ungrant it after releasing the
+	 * commit_iclog. The ctx may be freed by the time we return from
+	 * releasing the commit_iclog (i.e. checkpoint has been completed and
+	 * callback run) so we can't reference the ctx after the call to
+	 * xlog_state_release_iclog().
+	 */
+	ticket = ctx->ticket;
+
+	/*
+	 * If the checkpoint spans multiple iclogs, wait for all previous iclogs
+	 * to complete before we submit the commit_iclog. We can't use state
+	 * checks for this - ACTIVE can be either a past completed iclog or a
+	 * future iclog being filled, while WANT_SYNC through SYNC_DONE can be a
+	 * past or future iclog awaiting IO or ordered IO completion to be run.
+	 * In the latter case, if it's a future iclog and we wait on it, the we
+	 * will hang because it won't get processed through to ic_force_wait
+	 * wakeup until this commit_iclog is written to disk.  Hence we use the
+	 * iclog header lsn and compare it to the commit lsn to determine if we
+	 * need to wait on iclogs or not.
+	 */
+	spin_lock(&log->l_icloglock);
+	if (ctx->start_lsn != ctx->commit_lsn) {
+		xfs_lsn_t	plsn;
+
+		plsn = be64_to_cpu(ctx->commit_iclog->ic_prev->ic_header.h_lsn);
+		if (plsn && XFS_LSN_CMP(plsn, ctx->commit_lsn) < 0) {
+			/*
+			 * Waiting on ic_force_wait orders the completion of
+			 * iclogs older than ic_prev. Hence we only need to wait
+			 * on the most recent older iclog here.
+			 */
+			xlog_wait_on_iclog(ctx->commit_iclog->ic_prev);
+			spin_lock(&log->l_icloglock);
+		}
+
+		/*
+		 * We need to issue a pre-flush so that the ordering for this
+		 * checkpoint is correctly preserved down to stable storage.
+		 */
+		ctx->commit_iclog->ic_flags |= XLOG_ICL_NEED_FLUSH;
+	}
+
+	/*
+	 * The commit iclog must be written to stable storage to guarantee
+	 * journal IO vs metadata writeback IO is correctly ordered on stable
+	 * storage.
+	 *
+	 * If the push caller needs the commit to be immediately stable and the
+	 * commit_iclog is not yet marked as XLOG_STATE_WANT_SYNC to indicate it
+	 * will be written when released, switch it's state to WANT_SYNC right
+	 * now.
+	 */
+	ctx->commit_iclog->ic_flags |= XLOG_ICL_NEED_FUA;
+	if (push_commit_stable &&
+	    ctx->commit_iclog->ic_state == XLOG_STATE_ACTIVE)
+		xlog_state_switch_iclogs(log, ctx->commit_iclog, 0);
+	ticket = ctx->ticket;
+	xlog_state_release_iclog(log, ctx->commit_iclog, ticket);
+
+	/* Not safe to reference ctx now! */
+
+	spin_unlock(&log->l_icloglock);
+	xlog_cil_cleanup_whiteouts(&whiteouts);
+	xfs_log_ticket_ungrant(log, ticket);
+	return;
+
+out_skip:
+	up_write(&cil->xc_ctx_lock);
+	xfs_log_ticket_put(new_ctx->ticket);
+	kmem_free(new_ctx);
+	return;
+
+out_abort_free_ticket:
+	ASSERT(xlog_is_shutdown(log));
+	xlog_cil_cleanup_whiteouts(&whiteouts);
+	if (!ctx->commit_iclog) {
+		xfs_log_ticket_ungrant(log, ctx->ticket);
+		xlog_cil_committed(ctx);
+		return;
+	}
+	spin_lock(&log->l_icloglock);
+	ticket = ctx->ticket;
+	xlog_state_release_iclog(log, ctx->commit_iclog, ticket);
+	/* Not safe to reference ctx now! */
+	spin_unlock(&log->l_icloglock);
+	xfs_log_ticket_ungrant(log, ticket);
+}
+
+/*
+ * We need to push CIL every so often so we don't cache more than we can fit in
+ * the log. The limit really is that a checkpoint can't be more than half the
+ * log (the current checkpoint is not allowed to overwrite the previous
+ * checkpoint), but commit latency and memory usage limit this to a smaller
+ * size.
+ */
+static void
+xlog_cil_push_background(
+	struct xlog	*log) __releases(cil->xc_ctx_lock)
+{
+	struct xfs_cil	*cil = log->l_cilp;
+	int		space_used = atomic_read(&cil->xc_ctx->space_used);
+
+	/*
+	 * The cil won't be empty because we are called while holding the
+	 * context lock so whatever we added to the CIL will still be there.
+	 */
+	ASSERT(!test_bit(XLOG_CIL_EMPTY, &cil->xc_flags));
+
+	/*
+	 * We are done if:
+	 * - we haven't used up all the space available yet; or
+	 * - we've already queued up a push; and
+	 * - we're not over the hard limit; and
+	 * - nothing has been over the hard limit.
+	 *
+	 * If so, we don't need to take the push lock as there's nothing to do.
+	 */
+	if (space_used < XLOG_CIL_SPACE_LIMIT(log) ||
+	    (cil->xc_push_seq == cil->xc_current_sequence &&
+	     space_used < XLOG_CIL_BLOCKING_SPACE_LIMIT(log) &&
+	     !waitqueue_active(&cil->xc_push_wait))) {
+		up_read(&cil->xc_ctx_lock);
+		return;
+	}
+
+	spin_lock(&cil->xc_push_lock);
+	if (cil->xc_push_seq < cil->xc_current_sequence) {
+		cil->xc_push_seq = cil->xc_current_sequence;
+		queue_work(cil->xc_push_wq, &cil->xc_ctx->push_work);
+	}
+
+	/*
+	 * Drop the context lock now, we can't hold that if we need to sleep
+	 * because we are over the blocking threshold. The push_lock is still
+	 * held, so blocking threshold sleep/wakeup is still correctly
+	 * serialised here.
+	 */
+	up_read(&cil->xc_ctx_lock);
+
+	/*
+	 * If we are well over the space limit, throttle the work that is being
+	 * done until the push work on this context has begun. Enforce the hard
+	 * throttle on all transaction commits once it has been activated, even
+	 * if the committing transactions have resulted in the space usage
+	 * dipping back down under the hard limit.
+	 *
+	 * The ctx->xc_push_lock provides the serialisation necessary for safely
+	 * calling xlog_cil_over_hard_limit() in this context.
+	 */
+	if (xlog_cil_over_hard_limit(log, space_used)) {
+		trace_xfs_log_cil_wait(log, cil->xc_ctx->ticket);
+		ASSERT(space_used < log->l_logsize);
+		xlog_wait(&cil->xc_push_wait, &cil->xc_push_lock);
+		return;
+	}
+
+	spin_unlock(&cil->xc_push_lock);
+
+}
+
+/*
+ * xlog_cil_push_now() is used to trigger an immediate CIL push to the sequence
+ * number that is passed. When it returns, the work will be queued for
+ * @push_seq, but it won't be completed.
+ *
+ * If the caller is performing a synchronous force, we will flush the workqueue
+ * to get previously queued work moving to minimise the wait time they will
+ * undergo waiting for all outstanding pushes to complete. The caller is
+ * expected to do the required waiting for push_seq to complete.
+ *
+ * If the caller is performing an async push, we need to ensure that the
+ * checkpoint is fully flushed out of the iclogs when we finish the push. If we
+ * don't do this, then the commit record may remain sitting in memory in an
+ * ACTIVE iclog. This then requires another full log force to push to disk,
+ * which defeats the purpose of having an async, non-blocking CIL force
+ * mechanism. Hence in this case we need to pass a flag to the push work to
+ * indicate it needs to flush the commit record itself.
+ */
+static void
+xlog_cil_push_now(
+	struct xlog	*log,
+	xfs_lsn_t	push_seq,
+	bool		async)
+{
+	struct xfs_cil	*cil = log->l_cilp;
+
+	if (!cil)
+		return;
+
+	ASSERT(push_seq && push_seq <= cil->xc_current_sequence);
+
+	/* start on any pending background push to minimise wait time on it */
+	if (!async)
+		flush_workqueue(cil->xc_push_wq);
+
+	spin_lock(&cil->xc_push_lock);
+
+	/*
+	 * If this is an async flush request, we always need to set the
+	 * xc_push_commit_stable flag even if something else has already queued
+	 * a push. The flush caller is asking for the CIL to be on stable
+	 * storage when the next push completes, so regardless of who has queued
+	 * the push, the flush requires stable semantics from it.
+	 */
+	cil->xc_push_commit_stable = async;
+
+	/*
+	 * If the CIL is empty or we've already pushed the sequence then
+	 * there's no more work that we need to do.
+	 */
+	if (test_bit(XLOG_CIL_EMPTY, &cil->xc_flags) ||
+	    push_seq <= cil->xc_push_seq) {
+		spin_unlock(&cil->xc_push_lock);
+		return;
+	}
+
+	cil->xc_push_seq = push_seq;
+	queue_work(cil->xc_push_wq, &cil->xc_ctx->push_work);
+	spin_unlock(&cil->xc_push_lock);
+}
+
+bool
+xlog_cil_empty(
+	struct xlog	*log)
+{
+	struct xfs_cil	*cil = log->l_cilp;
+	bool		empty = false;
+
+	spin_lock(&cil->xc_push_lock);
+	if (test_bit(XLOG_CIL_EMPTY, &cil->xc_flags))
+		empty = true;
+	spin_unlock(&cil->xc_push_lock);
+	return empty;
+}
+
+/*
+ * If there are intent done items in this transaction and the related intent was
+ * committed in the current (same) CIL checkpoint, we don't need to write either
+ * the intent or intent done item to the journal as the change will be
+ * journalled atomically within this checkpoint. As we cannot remove items from
+ * the CIL here, mark the related intent with a whiteout so that the CIL push
+ * can remove it rather than writing it to the journal. Then remove the intent
+ * done item from the current transaction and release it so it doesn't get put
+ * into the CIL at all.
+ */
+static uint32_t
+xlog_cil_process_intents(
+	struct xfs_cil		*cil,
+	struct xfs_trans	*tp)
+{
+	struct xfs_log_item	*lip, *ilip, *next;
+	uint32_t		len = 0;
+
+	list_for_each_entry_safe(lip, next, &tp->t_items, li_trans) {
+		if (!(lip->li_ops->flags & XFS_ITEM_INTENT_DONE))
+			continue;
+
+		ilip = lip->li_ops->iop_intent(lip);
+		if (!ilip || !xlog_item_in_current_chkpt(cil, ilip))
+			continue;
+		set_bit(XFS_LI_WHITEOUT, &ilip->li_flags);
+		trace_xfs_cil_whiteout_mark(ilip);
+		len += ilip->li_lv->lv_bytes;
+		kmem_free(ilip->li_lv);
+		ilip->li_lv = NULL;
+
+		xfs_trans_del_item(lip);
+		lip->li_ops->iop_release(lip);
+	}
+	return len;
+}
+
+/*
+ * Commit a transaction with the given vector to the Committed Item List.
+ *
+ * To do this, we need to format the item, pin it in memory if required and
+ * account for the space used by the transaction. Once we have done that we
+ * need to release the unused reservation for the transaction, attach the
+ * transaction to the checkpoint context so we carry the busy extents through
+ * to checkpoint completion, and then unlock all the items in the transaction.
+ *
+ * Called with the context lock already held in read mode to lock out
+ * background commit, returns without it held once background commits are
+ * allowed again.
+ */
+void
+xlog_cil_commit(
+	struct xlog		*log,
+	struct xfs_trans	*tp,
+	xfs_csn_t		*commit_seq,
+	bool			regrant)
+{
+	struct xfs_cil		*cil = log->l_cilp;
+	struct xfs_log_item	*lip, *next;
+	uint32_t		released_space = 0;
+
+	/*
+	 * Do all necessary memory allocation before we lock the CIL.
+	 * This ensures the allocation does not deadlock with a CIL
+	 * push in memory reclaim (e.g. from kswapd).
+	 */
+	xlog_cil_alloc_shadow_bufs(log, tp);
+
+	/* lock out background commit */
+	down_read(&cil->xc_ctx_lock);
+
+	if (tp->t_flags & XFS_TRANS_HAS_INTENT_DONE)
+		released_space = xlog_cil_process_intents(cil, tp);
+
+	xlog_cil_insert_items(log, tp, released_space);
+
+	if (regrant && !xlog_is_shutdown(log))
+		xfs_log_ticket_regrant(log, tp->t_ticket);
+	else
+		xfs_log_ticket_ungrant(log, tp->t_ticket);
+	tp->t_ticket = NULL;
+	xfs_trans_unreserve_and_mod_sb(tp);
+
+	/*
+	 * Once all the items of the transaction have been copied to the CIL,
+	 * the items can be unlocked and possibly freed.
+	 *
+	 * This needs to be done before we drop the CIL context lock because we
+	 * have to update state in the log items and unlock them before they go
+	 * to disk. If we don't, then the CIL checkpoint can race with us and
+	 * we can run checkpoint completion before we've updated and unlocked
+	 * the log items. This affects (at least) processing of stale buffers,
+	 * inodes and EFIs.
+	 */
+	trace_xfs_trans_commit_items(tp, _RET_IP_);
+	list_for_each_entry_safe(lip, next, &tp->t_items, li_trans) {
+		xfs_trans_del_item(lip);
+		if (lip->li_ops->iop_committing)
+			lip->li_ops->iop_committing(lip, cil->xc_ctx->sequence);
+	}
+	if (commit_seq)
+		*commit_seq = cil->xc_ctx->sequence;
+
+	/* xlog_cil_push_background() releases cil->xc_ctx_lock */
+	xlog_cil_push_background(log);
+}
+
+/*
+ * Flush the CIL to stable storage but don't wait for it to complete. This
+ * requires the CIL push to ensure the commit record for the push hits the disk,
+ * but otherwise is no different to a push done from a log force.
+ */
+void
+xlog_cil_flush(
+	struct xlog	*log)
+{
+	xfs_csn_t	seq = log->l_cilp->xc_current_sequence;
+
+	trace_xfs_log_force(log->l_mp, seq, _RET_IP_);
+	xlog_cil_push_now(log, seq, true);
+
+	/*
+	 * If the CIL is empty, make sure that any previous checkpoint that may
+	 * still be in an active iclog is pushed to stable storage.
+	 */
+	if (test_bit(XLOG_CIL_EMPTY, &log->l_cilp->xc_flags))
+		xfs_log_force(log->l_mp, 0);
+}
+
+/*
+ * Conditionally push the CIL based on the sequence passed in.
+ *
+ * We only need to push if we haven't already pushed the sequence number given.
+ * Hence the only time we will trigger a push here is if the push sequence is
+ * the same as the current context.
+ *
+ * We return the current commit lsn to allow the callers to determine if a
+ * iclog flush is necessary following this call.
+ */
+xfs_lsn_t
+xlog_cil_force_seq(
+	struct xlog	*log,
+	xfs_csn_t	sequence)
+{
+	struct xfs_cil		*cil = log->l_cilp;
+	struct xfs_cil_ctx	*ctx;
+	xfs_lsn_t		commit_lsn = NULLCOMMITLSN;
+
+	ASSERT(sequence <= cil->xc_current_sequence);
+
+	if (!sequence)
+		sequence = cil->xc_current_sequence;
+	trace_xfs_log_force(log->l_mp, sequence, _RET_IP_);
+
+	/*
+	 * check to see if we need to force out the current context.
+	 * xlog_cil_push() handles racing pushes for the same sequence,
+	 * so no need to deal with it here.
+	 */
+restart:
+	xlog_cil_push_now(log, sequence, false);
+
+	/*
+	 * See if we can find a previous sequence still committing.
+	 * We need to wait for all previous sequence commits to complete
+	 * before allowing the force of push_seq to go ahead. Hence block
+	 * on commits for those as well.
+	 */
+	spin_lock(&cil->xc_push_lock);
+	list_for_each_entry(ctx, &cil->xc_committing, committing) {
+		/*
+		 * Avoid getting stuck in this loop because we were woken by the
+		 * shutdown, but then went back to sleep once already in the
+		 * shutdown state.
+		 */
+		if (xlog_is_shutdown(log))
+			goto out_shutdown;
+		if (ctx->sequence > sequence)
+			continue;
+		if (!ctx->commit_lsn) {
+			/*
+			 * It is still being pushed! Wait for the push to
+			 * complete, then start again from the beginning.
+			 */
+			XFS_STATS_INC(log->l_mp, xs_log_force_sleep);
+			xlog_wait(&cil->xc_commit_wait, &cil->xc_push_lock);
+			goto restart;
+		}
+		if (ctx->sequence != sequence)
+			continue;
+		/* found it! */
+		commit_lsn = ctx->commit_lsn;
+	}
+
+	/*
+	 * The call to xlog_cil_push_now() executes the push in the background.
+	 * Hence by the time we have got here it our sequence may not have been
+	 * pushed yet. This is true if the current sequence still matches the
+	 * push sequence after the above wait loop and the CIL still contains
+	 * dirty objects. This is guaranteed by the push code first adding the
+	 * context to the committing list before emptying the CIL.
+	 *
+	 * Hence if we don't find the context in the committing list and the
+	 * current sequence number is unchanged then the CIL contents are
+	 * significant.  If the CIL is empty, if means there was nothing to push
+	 * and that means there is nothing to wait for. If the CIL is not empty,
+	 * it means we haven't yet started the push, because if it had started
+	 * we would have found the context on the committing list.
+	 */
+	if (sequence == cil->xc_current_sequence &&
+	    !test_bit(XLOG_CIL_EMPTY, &cil->xc_flags)) {
+		spin_unlock(&cil->xc_push_lock);
+		goto restart;
+	}
+
+	spin_unlock(&cil->xc_push_lock);
+	return commit_lsn;
+
+	/*
+	 * We detected a shutdown in progress. We need to trigger the log force
+	 * to pass through it's iclog state machine error handling, even though
+	 * we are already in a shutdown state. Hence we can't return
+	 * NULLCOMMITLSN here as that has special meaning to log forces (i.e.
+	 * LSN is already stable), so we return a zero LSN instead.
+	 */
+out_shutdown:
+	spin_unlock(&cil->xc_push_lock);
+	return 0;
+}
+
+/*
+ * Move dead percpu state to the relevant CIL context structures.
+ *
+ * We have to lock the CIL context here to ensure that nothing is modifying
+ * the percpu state, either addition or removal. Both of these are done under
+ * the CIL context lock, so grabbing that exclusively here will ensure we can
+ * safely drain the cilpcp for the CPU that is dying.
+ */
+void
+xlog_cil_pcp_dead(
+	struct xlog		*log,
+	unsigned int		cpu)
+{
+	struct xfs_cil		*cil = log->l_cilp;
+	struct xlog_cil_pcp	*cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
+	struct xfs_cil_ctx	*ctx;
+
+	down_write(&cil->xc_ctx_lock);
+	ctx = cil->xc_ctx;
+	if (ctx->ticket)
+		ctx->ticket->t_curr_res += cilpcp->space_reserved;
+	cilpcp->space_reserved = 0;
+
+	if (!list_empty(&cilpcp->log_items))
+		list_splice_init(&cilpcp->log_items, &ctx->log_items);
+	if (!list_empty(&cilpcp->busy_extents))
+		list_splice_init(&cilpcp->busy_extents, &ctx->busy_extents);
+	atomic_add(cilpcp->space_used, &ctx->space_used);
+	cilpcp->space_used = 0;
+	up_write(&cil->xc_ctx_lock);
+}
+
+/*
+ * Perform initial CIL structure initialisation.
+ */
+int
+xlog_cil_init(
+	struct xlog		*log)
+{
+	struct xfs_cil		*cil;
+	struct xfs_cil_ctx	*ctx;
+	struct xlog_cil_pcp	*cilpcp;
+	int			cpu;
+
+	cil = kmem_zalloc(sizeof(*cil), KM_MAYFAIL);
+	if (!cil)
+		return -ENOMEM;
+	/*
+	 * Limit the CIL pipeline depth to 4 concurrent works to bound the
+	 * concurrency the log spinlocks will be exposed to.
+	 */
+	cil->xc_push_wq = alloc_workqueue("xfs-cil/%s",
+			XFS_WQFLAGS(WQ_FREEZABLE | WQ_MEM_RECLAIM | WQ_UNBOUND),
+			4, log->l_mp->m_super->s_id);
+	if (!cil->xc_push_wq)
+		goto out_destroy_cil;
+
+	cil->xc_log = log;
+	cil->xc_pcp = alloc_percpu(struct xlog_cil_pcp);
+	if (!cil->xc_pcp)
+		goto out_destroy_wq;
+
+	for_each_possible_cpu(cpu) {
+		cilpcp = per_cpu_ptr(cil->xc_pcp, cpu);
+		INIT_LIST_HEAD(&cilpcp->busy_extents);
+		INIT_LIST_HEAD(&cilpcp->log_items);
+	}
+
+	INIT_LIST_HEAD(&cil->xc_committing);
+	spin_lock_init(&cil->xc_push_lock);
+	init_waitqueue_head(&cil->xc_push_wait);
+	init_rwsem(&cil->xc_ctx_lock);
+	init_waitqueue_head(&cil->xc_start_wait);
+	init_waitqueue_head(&cil->xc_commit_wait);
+	log->l_cilp = cil;
+
+	ctx = xlog_cil_ctx_alloc();
+	xlog_cil_ctx_switch(cil, ctx);
+	return 0;
+
+out_destroy_wq:
+	destroy_workqueue(cil->xc_push_wq);
+out_destroy_cil:
+	kmem_free(cil);
+	return -ENOMEM;
+}
+
+void
+xlog_cil_destroy(
+	struct xlog	*log)
+{
+	struct xfs_cil	*cil = log->l_cilp;
+
+	if (cil->xc_ctx) {
+		if (cil->xc_ctx->ticket)
+			xfs_log_ticket_put(cil->xc_ctx->ticket);
+		kmem_free(cil->xc_ctx);
+	}
+
+	ASSERT(test_bit(XLOG_CIL_EMPTY, &cil->xc_flags));
+	free_percpu(cil->xc_pcp);
+	destroy_workqueue(cil->xc_push_wq);
+	kmem_free(cil);
+}
+