Adding upstream version 4.19.249.upstream/4.19.249

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

1 files changed, 607 insertions, 0 deletions

diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h
new file mode 100644
index 000000000..b5f82cb36
--- /dev/null
+++ b/fs/xfs/xfs_log_priv.h
@@ -0,0 +1,607 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2000-2003,2005 Silicon Graphics, Inc.
+ * All Rights Reserved.
+ */
+#ifndef	__XFS_LOG_PRIV_H__
+#define __XFS_LOG_PRIV_H__
+
+struct xfs_buf;
+struct xlog;
+struct xlog_ticket;
+struct xfs_mount;
+struct xfs_log_callback;
+
+/*
+ * Flags for log structure
+ */
+#define XLOG_ACTIVE_RECOVERY	0x2	/* in the middle of recovery */
+#define	XLOG_RECOVERY_NEEDED	0x4	/* log was recovered */
+#define XLOG_IO_ERROR		0x8	/* log hit an I/O error, and being
+					   shutdown */
+#define XLOG_TAIL_WARN		0x10	/* log tail verify warning issued */
+
+/*
+ * get client id from packed copy.
+ *
+ * this hack is here because the xlog_pack code copies four bytes
+ * of xlog_op_header containing the fields oh_clientid, oh_flags
+ * and oh_res2 into the packed copy.
+ *
+ * later on this four byte chunk is treated as an int and the
+ * client id is pulled out.
+ *
+ * this has endian issues, of course.
+ */
+static inline uint xlog_get_client_id(__be32 i)
+{
+	return be32_to_cpu(i) >> 24;
+}
+
+/*
+ * In core log state
+ */
+#define XLOG_STATE_ACTIVE    0x0001 /* Current IC log being written to */
+#define XLOG_STATE_WANT_SYNC 0x0002 /* Want to sync this iclog; no more writes */
+#define XLOG_STATE_SYNCING   0x0004 /* This IC log is syncing */
+#define XLOG_STATE_DONE_SYNC 0x0008 /* Done syncing to disk */
+#define XLOG_STATE_DO_CALLBACK \
+			     0x0010 /* Process callback functions */
+#define XLOG_STATE_CALLBACK  0x0020 /* Callback functions now */
+#define XLOG_STATE_DIRTY     0x0040 /* Dirty IC log, not ready for ACTIVE status*/
+#define XLOG_STATE_IOERROR   0x0080 /* IO error happened in sync'ing log */
+#define XLOG_STATE_IOABORT   0x0100 /* force abort on I/O completion (debug) */
+#define XLOG_STATE_ALL	     0x7FFF /* All possible valid flags */
+#define XLOG_STATE_NOTUSED   0x8000 /* This IC log not being used */
+
+/*
+ * Flags to log ticket
+ */
+#define XLOG_TIC_INITED		0x1	/* has been initialized */
+#define XLOG_TIC_PERM_RESERV	0x2	/* permanent reservation */
+
+#define XLOG_TIC_FLAGS \
+	{ XLOG_TIC_INITED,	"XLOG_TIC_INITED" }, \
+	{ XLOG_TIC_PERM_RESERV,	"XLOG_TIC_PERM_RESERV" }
+
+/*
+ * Below are states for covering allocation transactions.
+ * By covering, we mean changing the h_tail_lsn in the last on-disk
+ * log write such that no allocation transactions will be re-done during
+ * recovery after a system crash. Recovery starts at the last on-disk
+ * log write.
+ *
+ * These states are used to insert dummy log entries to cover
+ * space allocation transactions which can undo non-transactional changes
+ * after a crash. Writes to a file with space
+ * already allocated do not result in any transactions. Allocations
+ * might include space beyond the EOF. So if we just push the EOF a
+ * little, the last transaction for the file could contain the wrong
+ * size. If there is no file system activity, after an allocation
+ * transaction, and the system crashes, the allocation transaction
+ * will get replayed and the file will be truncated. This could
+ * be hours/days/... after the allocation occurred.
+ *
+ * The fix for this is to do two dummy transactions when the
+ * system is idle. We need two dummy transaction because the h_tail_lsn
+ * in the log record header needs to point beyond the last possible
+ * non-dummy transaction. The first dummy changes the h_tail_lsn to
+ * the first transaction before the dummy. The second dummy causes
+ * h_tail_lsn to point to the first dummy. Recovery starts at h_tail_lsn.
+ *
+ * These dummy transactions get committed when everything
+ * is idle (after there has been some activity).
+ *
+ * There are 5 states used to control this.
+ *
+ *  IDLE -- no logging has been done on the file system or
+ *		we are done covering previous transactions.
+ *  NEED -- logging has occurred and we need a dummy transaction
+ *		when the log becomes idle.
+ *  DONE -- we were in the NEED state and have committed a dummy
+ *		transaction.
+ *  NEED2 -- we detected that a dummy transaction has gone to the
+ *		on disk log with no other transactions.
+ *  DONE2 -- we committed a dummy transaction when in the NEED2 state.
+ *
+ * There are two places where we switch states:
+ *
+ * 1.) In xfs_sync, when we detect an idle log and are in NEED or NEED2.
+ *	We commit the dummy transaction and switch to DONE or DONE2,
+ *	respectively. In all other states, we don't do anything.
+ *
+ * 2.) When we finish writing the on-disk log (xlog_state_clean_log).
+ *
+ *	No matter what state we are in, if this isn't the dummy
+ *	transaction going out, the next state is NEED.
+ *	So, if we aren't in the DONE or DONE2 states, the next state
+ *	is NEED. We can't be finishing a write of the dummy record
+ *	unless it was committed and the state switched to DONE or DONE2.
+ *
+ *	If we are in the DONE state and this was a write of the
+ *		dummy transaction, we move to NEED2.
+ *
+ *	If we are in the DONE2 state and this was a write of the
+ *		dummy transaction, we move to IDLE.
+ *
+ *
+ * Writing only one dummy transaction can get appended to
+ * one file space allocation. When this happens, the log recovery
+ * code replays the space allocation and a file could be truncated.
+ * This is why we have the NEED2 and DONE2 states before going idle.
+ */
+
+#define XLOG_STATE_COVER_IDLE	0
+#define XLOG_STATE_COVER_NEED	1
+#define XLOG_STATE_COVER_DONE	2
+#define XLOG_STATE_COVER_NEED2	3
+#define XLOG_STATE_COVER_DONE2	4
+
+#define XLOG_COVER_OPS		5
+
+/* Ticket reservation region accounting */ 
+#define XLOG_TIC_LEN_MAX	15
+
+/*
+ * Reservation region
+ * As would be stored in xfs_log_iovec but without the i_addr which
+ * we don't care about.
+ */
+typedef struct xlog_res {
+	uint	r_len;	/* region length		:4 */
+	uint	r_type;	/* region's transaction type	:4 */
+} xlog_res_t;
+
+typedef struct xlog_ticket {
+	struct list_head   t_queue;	 /* reserve/write queue */
+	struct task_struct *t_task;	 /* task that owns this ticket */
+	xlog_tid_t	   t_tid;	 /* transaction identifier	 : 4  */
+	atomic_t	   t_ref;	 /* ticket reference count       : 4  */
+	int		   t_curr_res;	 /* current reservation in bytes : 4  */
+	int		   t_unit_res;	 /* unit reservation in bytes    : 4  */
+	char		   t_ocnt;	 /* original count		 : 1  */
+	char		   t_cnt;	 /* current count		 : 1  */
+	char		   t_clientid;	 /* who does this belong to;	 : 1  */
+	char		   t_flags;	 /* properties of reservation	 : 1  */
+
+        /* reservation array fields */
+	uint		   t_res_num;                    /* num in array : 4 */
+	uint		   t_res_num_ophdrs;		 /* num op hdrs  : 4 */
+	uint		   t_res_arr_sum;		 /* array sum    : 4 */
+	uint		   t_res_o_flow;		 /* sum overflow : 4 */
+	xlog_res_t	   t_res_arr[XLOG_TIC_LEN_MAX];  /* array of res : 8 * 15 */ 
+} xlog_ticket_t;
+
+/*
+ * - A log record header is 512 bytes.  There is plenty of room to grow the
+ *	xlog_rec_header_t into the reserved space.
+ * - ic_data follows, so a write to disk can start at the beginning of
+ *	the iclog.
+ * - ic_forcewait is used to implement synchronous forcing of the iclog to disk.
+ * - ic_next is the pointer to the next iclog in the ring.
+ * - ic_bp is a pointer to the buffer used to write this incore log to disk.
+ * - ic_log is a pointer back to the global log structure.
+ * - ic_callback is a linked list of callback function/argument pairs to be
+ *	called after an iclog finishes writing.
+ * - ic_size is the full size of the header plus data.
+ * - ic_offset is the current number of bytes written to in this iclog.
+ * - ic_refcnt is bumped when someone is writing to the log.
+ * - ic_state is the state of the iclog.
+ *
+ * Because of cacheline contention on large machines, we need to separate
+ * various resources onto different cachelines. To start with, make the
+ * structure cacheline aligned. The following fields can be contended on
+ * by independent processes:
+ *
+ *	- ic_callback_*
+ *	- ic_refcnt
+ *	- fields protected by the global l_icloglock
+ *
+ * so we need to ensure that these fields are located in separate cachelines.
+ * We'll put all the read-only and l_icloglock fields in the first cacheline,
+ * and move everything else out to subsequent cachelines.
+ */
+typedef struct xlog_in_core {
+	wait_queue_head_t	ic_force_wait;
+	wait_queue_head_t	ic_write_wait;
+	struct xlog_in_core	*ic_next;
+	struct xlog_in_core	*ic_prev;
+	struct xfs_buf		*ic_bp;
+	struct xlog		*ic_log;
+	int			ic_size;
+	int			ic_offset;
+	int			ic_bwritecnt;
+	unsigned short		ic_state;
+	char			*ic_datap;	/* pointer to iclog data */
+
+	/* Callback structures need their own cacheline */
+	spinlock_t		ic_callback_lock ____cacheline_aligned_in_smp;
+	struct xfs_log_callback	*ic_callback;
+	struct xfs_log_callback	**ic_callback_tail;
+
+	/* reference counts need their own cacheline */
+	atomic_t		ic_refcnt ____cacheline_aligned_in_smp;
+	xlog_in_core_2_t	*ic_data;
+#define ic_header	ic_data->hic_header
+} xlog_in_core_t;
+
+/*
+ * The CIL context is used to aggregate per-transaction details as well be
+ * passed to the iclog for checkpoint post-commit processing.  After being
+ * passed to the iclog, another context needs to be allocated for tracking the
+ * next set of transactions to be aggregated into a checkpoint.
+ */
+struct xfs_cil;
+
+struct xfs_cil_ctx {
+	struct xfs_cil		*cil;
+	xfs_lsn_t		sequence;	/* chkpt sequence # */
+	xfs_lsn_t		start_lsn;	/* first LSN of chkpt commit */
+	xfs_lsn_t		commit_lsn;	/* chkpt commit record lsn */
+	struct xlog_ticket	*ticket;	/* chkpt ticket */
+	int			nvecs;		/* number of regions */
+	int			space_used;	/* aggregate size of regions */
+	struct list_head	busy_extents;	/* busy extents in chkpt */
+	struct xfs_log_vec	*lv_chain;	/* logvecs being pushed */
+	struct xfs_log_callback	log_cb;		/* completion callback hook. */
+	struct list_head	committing;	/* ctx committing list */
+	struct work_struct	discard_endio_work;
+};
+
+/*
+ * Committed Item List structure
+ *
+ * This structure is used to track log items that have been committed but not
+ * yet written into the log. It is used only when the delayed logging mount
+ * option is enabled.
+ *
+ * This structure tracks the list of committing checkpoint contexts so
+ * we can avoid the problem of having to hold out new transactions during a
+ * flush until we have a the commit record LSN of the checkpoint. We can
+ * traverse the list of committing contexts in xlog_cil_push_lsn() to find a
+ * sequence match and extract the commit LSN directly from there. If the
+ * checkpoint is still in the process of committing, we can block waiting for
+ * the commit LSN to be determined as well. This should make synchronous
+ * operations almost as efficient as the old logging methods.
+ */
+struct xfs_cil {
+	struct xlog		*xc_log;
+	struct list_head	xc_cil;
+	spinlock_t		xc_cil_lock;
+
+	struct rw_semaphore	xc_ctx_lock ____cacheline_aligned_in_smp;
+	struct xfs_cil_ctx	*xc_ctx;
+
+	spinlock_t		xc_push_lock ____cacheline_aligned_in_smp;
+	xfs_lsn_t		xc_push_seq;
+	struct list_head	xc_committing;
+	wait_queue_head_t	xc_commit_wait;
+	xfs_lsn_t		xc_current_sequence;
+	struct work_struct	xc_push_work;
+} ____cacheline_aligned_in_smp;
+
+/*
+ * The amount of log space we allow the CIL to aggregate is difficult to size.
+ * Whatever we choose, we have to make sure we can get a reservation for the
+ * log space effectively, that it is large enough to capture sufficient
+ * relogging to reduce log buffer IO significantly, but it is not too large for
+ * the log or induces too much latency when writing out through the iclogs. We
+ * track both space consumed and the number of vectors in the checkpoint
+ * context, so we need to decide which to use for limiting.
+ *
+ * Every log buffer we write out during a push needs a header reserved, which
+ * is at least one sector and more for v2 logs. Hence we need a reservation of
+ * at least 512 bytes per 32k of log space just for the LR headers. That means
+ * 16KB of reservation per megabyte of delayed logging space we will consume,
+ * plus various headers.  The number of headers will vary based on the num of
+ * io vectors, so limiting on a specific number of vectors is going to result
+ * in transactions of varying size. IOWs, it is more consistent to track and
+ * limit space consumed in the log rather than by the number of objects being
+ * logged in order to prevent checkpoint ticket overruns.
+ *
+ * Further, use of static reservations through the log grant mechanism is
+ * problematic. It introduces a lot of complexity (e.g. reserve grant vs write
+ * grant) and a significant deadlock potential because regranting write space
+ * can block on log pushes. Hence if we have to regrant log space during a log
+ * push, we can deadlock.
+ *
+ * However, we can avoid this by use of a dynamic "reservation stealing"
+ * technique during transaction commit whereby unused reservation space in the
+ * transaction ticket is transferred to the CIL ctx commit ticket to cover the
+ * space needed by the checkpoint transaction. This means that we never need to
+ * specifically reserve space for the CIL checkpoint transaction, nor do we
+ * need to regrant space once the checkpoint completes. This also means the
+ * checkpoint transaction ticket is specific to the checkpoint context, rather
+ * than the CIL itself.
+ *
+ * With dynamic reservations, we can effectively make up arbitrary limits for
+ * the checkpoint size so long as they don't violate any other size rules.
+ * Recovery imposes a rule that no transaction exceed half the log, so we are
+ * limited by that.  Furthermore, the log transaction reservation subsystem
+ * tries to keep 25% of the log free, so we need to keep below that limit or we
+ * risk running out of free log space to start any new transactions.
+ *
+ * In order to keep background CIL push efficient, we will set a lower
+ * threshold at which background pushing is attempted without blocking current
+ * transaction commits.  A separate, higher bound defines when CIL pushes are
+ * enforced to ensure we stay within our maximum checkpoint size bounds.
+ * threshold, yet give us plenty of space for aggregation on large logs.
+ */
+#define XLOG_CIL_SPACE_LIMIT(log)	(log->l_logsize >> 3)
+
+/*
+ * ticket grant locks, queues and accounting have their own cachlines
+ * as these are quite hot and can be operated on concurrently.
+ */
+struct xlog_grant_head {
+	spinlock_t		lock ____cacheline_aligned_in_smp;
+	struct list_head	waiters;
+	atomic64_t		grant;
+};
+
+/*
+ * The reservation head lsn is not made up of a cycle number and block number.
+ * Instead, it uses a cycle number and byte number.  Logs don't expect to
+ * overflow 31 bits worth of byte offset, so using a byte number will mean
+ * that round off problems won't occur when releasing partial reservations.
+ */
+struct xlog {
+	/* The following fields don't need locking */
+	struct xfs_mount	*l_mp;	        /* mount point */
+	struct xfs_ail		*l_ailp;	/* AIL log is working with */
+	struct xfs_cil		*l_cilp;	/* CIL log is working with */
+	struct xfs_buf		*l_xbuf;        /* extra buffer for log
+						 * wrapping */
+	struct xfs_buftarg	*l_targ;        /* buftarg of log */
+	struct delayed_work	l_work;		/* background flush work */
+	uint			l_flags;
+	uint			l_quotaoffs_flag; /* XFS_DQ_*, for QUOTAOFFs */
+	struct list_head	*l_buf_cancel_table;
+	int			l_iclog_hsize;  /* size of iclog header */
+	int			l_iclog_heads;  /* # of iclog header sectors */
+	uint			l_sectBBsize;   /* sector size in BBs (2^n) */
+	int			l_iclog_size;	/* size of log in bytes */
+	int			l_iclog_size_log; /* log power size of log */
+	int			l_iclog_bufs;	/* number of iclog buffers */
+	xfs_daddr_t		l_logBBstart;   /* start block of log */
+	int			l_logsize;      /* size of log in bytes */
+	int			l_logBBsize;    /* size of log in BB chunks */
+
+	/* The following block of fields are changed while holding icloglock */
+	wait_queue_head_t	l_flush_wait ____cacheline_aligned_in_smp;
+						/* waiting for iclog flush */
+	int			l_covered_state;/* state of "covering disk
+						 * log entries" */
+	xlog_in_core_t		*l_iclog;       /* head log queue	*/
+	spinlock_t		l_icloglock;    /* grab to change iclog state */
+	int			l_curr_cycle;   /* Cycle number of log writes */
+	int			l_prev_cycle;   /* Cycle number before last
+						 * block increment */
+	int			l_curr_block;   /* current logical log block */
+	int			l_prev_block;   /* previous logical log block */
+
+	/*
+	 * l_last_sync_lsn and l_tail_lsn are atomics so they can be set and
+	 * read without needing to hold specific locks. To avoid operations
+	 * contending with other hot objects, place each of them on a separate
+	 * cacheline.
+	 */
+	/* lsn of last LR on disk */
+	atomic64_t		l_last_sync_lsn ____cacheline_aligned_in_smp;
+	/* lsn of 1st LR with unflushed * buffers */
+	atomic64_t		l_tail_lsn ____cacheline_aligned_in_smp;
+
+	struct xlog_grant_head	l_reserve_head;
+	struct xlog_grant_head	l_write_head;
+
+	struct xfs_kobj		l_kobj;
+
+	/* The following field are used for debugging; need to hold icloglock */
+#ifdef DEBUG
+	void			*l_iclog_bak[XLOG_MAX_ICLOGS];
+	/* log record crc error injection factor */
+	uint32_t		l_badcrc_factor;
+#endif
+	/* log recovery lsn tracking (for buffer submission */
+	xfs_lsn_t		l_recovery_lsn;
+};
+
+#define XLOG_BUF_CANCEL_BUCKET(log, blkno) \
+	((log)->l_buf_cancel_table + ((uint64_t)blkno % XLOG_BC_TABLE_SIZE))
+
+#define XLOG_FORCED_SHUTDOWN(log)	((log)->l_flags & XLOG_IO_ERROR)
+
+/* common routines */
+extern int
+xlog_recover(
+	struct xlog		*log);
+extern int
+xlog_recover_finish(
+	struct xlog		*log);
+extern int
+xlog_recover_cancel(struct xlog *);
+
+extern __le32	 xlog_cksum(struct xlog *log, struct xlog_rec_header *rhead,
+			    char *dp, int size);
+
+extern kmem_zone_t *xfs_log_ticket_zone;
+struct xlog_ticket *
+xlog_ticket_alloc(
+	struct xlog	*log,
+	int		unit_bytes,
+	int		count,
+	char		client,
+	bool		permanent,
+	xfs_km_flags_t	alloc_flags);
+
+
+static inline void
+xlog_write_adv_cnt(void **ptr, int *len, int *off, size_t bytes)
+{
+	*ptr += bytes;
+	*len -= bytes;
+	*off += bytes;
+}
+
+void	xlog_print_tic_res(struct xfs_mount *mp, struct xlog_ticket *ticket);
+void	xlog_print_trans(struct xfs_trans *);
+int
+xlog_write(
+	struct xlog		*log,
+	struct xfs_log_vec	*log_vector,
+	struct xlog_ticket	*tic,
+	xfs_lsn_t		*start_lsn,
+	struct xlog_in_core	**commit_iclog,
+	uint			flags);
+
+/*
+ * When we crack an atomic LSN, we sample it first so that the value will not
+ * change while we are cracking it into the component values. This means we
+ * will always get consistent component values to work from. This should always
+ * be used to sample and crack LSNs that are stored and updated in atomic
+ * variables.
+ */
+static inline void
+xlog_crack_atomic_lsn(atomic64_t *lsn, uint *cycle, uint *block)
+{
+	xfs_lsn_t val = atomic64_read(lsn);
+
+	*cycle = CYCLE_LSN(val);
+	*block = BLOCK_LSN(val);
+}
+
+/*
+ * Calculate and assign a value to an atomic LSN variable from component pieces.
+ */
+static inline void
+xlog_assign_atomic_lsn(atomic64_t *lsn, uint cycle, uint block)
+{
+	atomic64_set(lsn, xlog_assign_lsn(cycle, block));
+}
+
+/*
+ * When we crack the grant head, we sample it first so that the value will not
+ * change while we are cracking it into the component values. This means we
+ * will always get consistent component values to work from.
+ */
+static inline void
+xlog_crack_grant_head_val(int64_t val, int *cycle, int *space)
+{
+	*cycle = val >> 32;
+	*space = val & 0xffffffff;
+}
+
+static inline void
+xlog_crack_grant_head(atomic64_t *head, int *cycle, int *space)
+{
+	xlog_crack_grant_head_val(atomic64_read(head), cycle, space);
+}
+
+static inline int64_t
+xlog_assign_grant_head_val(int cycle, int space)
+{
+	return ((int64_t)cycle << 32) | space;
+}
+
+static inline void
+xlog_assign_grant_head(atomic64_t *head, int cycle, int space)
+{
+	atomic64_set(head, xlog_assign_grant_head_val(cycle, space));
+}
+
+/*
+ * Committed Item List interfaces
+ */
+int	xlog_cil_init(struct xlog *log);
+void	xlog_cil_init_post_recovery(struct xlog *log);
+void	xlog_cil_destroy(struct xlog *log);
+bool	xlog_cil_empty(struct xlog *log);
+
+/*
+ * CIL force routines
+ */
+xfs_lsn_t
+xlog_cil_force_lsn(
+	struct xlog *log,
+	xfs_lsn_t sequence);
+
+static inline void
+xlog_cil_force(struct xlog *log)
+{
+	xlog_cil_force_lsn(log, log->l_cilp->xc_current_sequence);
+}
+
+/*
+ * Unmount record type is used as a pseudo transaction type for the ticket.
+ * It's value must be outside the range of XFS_TRANS_* values.
+ */
+#define XLOG_UNMOUNT_REC_TYPE	(-1U)
+
+/*
+ * Wrapper function for waiting on a wait queue serialised against wakeups
+ * by a spinlock. This matches the semantics of all the wait queues used in the
+ * log code.
+ */
+static inline void xlog_wait(wait_queue_head_t *wq, spinlock_t *lock)
+{
+	DECLARE_WAITQUEUE(wait, current);
+
+	add_wait_queue_exclusive(wq, &wait);
+	__set_current_state(TASK_UNINTERRUPTIBLE);
+	spin_unlock(lock);
+	schedule();
+	remove_wait_queue(wq, &wait);
+}
+
+/*
+ * The LSN is valid so long as it is behind the current LSN. If it isn't, this
+ * means that the next log record that includes this metadata could have a
+ * smaller LSN. In turn, this means that the modification in the log would not
+ * replay.
+ */
+static inline bool
+xlog_valid_lsn(
+	struct xlog	*log,
+	xfs_lsn_t	lsn)
+{
+	int		cur_cycle;
+	int		cur_block;
+	bool		valid = true;
+
+	/*
+	 * First, sample the current lsn without locking to avoid added
+	 * contention from metadata I/O. The current cycle and block are updated
+	 * (in xlog_state_switch_iclogs()) and read here in a particular order
+	 * to avoid false negatives (e.g., thinking the metadata LSN is valid
+	 * when it is not).
+	 *
+	 * The current block is always rewound before the cycle is bumped in
+	 * xlog_state_switch_iclogs() to ensure the current LSN is never seen in
+	 * a transiently forward state. Instead, we can see the LSN in a
+	 * transiently behind state if we happen to race with a cycle wrap.
+	 */
+	cur_cycle = READ_ONCE(log->l_curr_cycle);
+	smp_rmb();
+	cur_block = READ_ONCE(log->l_curr_block);
+
+	if ((CYCLE_LSN(lsn) > cur_cycle) ||
+	    (CYCLE_LSN(lsn) == cur_cycle && BLOCK_LSN(lsn) > cur_block)) {
+		/*
+		 * If the metadata LSN appears invalid, it's possible the check
+		 * above raced with a wrap to the next log cycle. Grab the lock
+		 * to check for sure.
+		 */
+		spin_lock(&log->l_icloglock);
+		cur_cycle = log->l_curr_cycle;
+		cur_block = log->l_curr_block;
+		spin_unlock(&log->l_icloglock);
+
+		if ((CYCLE_LSN(lsn) > cur_cycle) ||
+		    (CYCLE_LSN(lsn) == cur_cycle && BLOCK_LSN(lsn) > cur_block))
+			valid = false;
+	}
+
+	return valid;
+}
+
+#endif	/* __XFS_LOG_PRIV_H__ */