From 2c3c1048746a4622d8c89a29670120dc8fab93c4 Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Sun, 7 Apr 2024 20:49:45 +0200 Subject: Adding upstream version 6.1.76. Signed-off-by: Daniel Baumann --- fs/btrfs/locking.c | 405 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 405 insertions(+) create mode 100644 fs/btrfs/locking.c (limited to 'fs/btrfs/locking.c') diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c new file mode 100644 index 000000000..df98e64d7 --- /dev/null +++ b/fs/btrfs/locking.c @@ -0,0 +1,405 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2008 Oracle. All rights reserved. + */ + +#include +#include +#include +#include +#include +#include "misc.h" +#include "ctree.h" +#include "extent_io.h" +#include "locking.h" + +/* + * Lockdep class keys for extent_buffer->lock's in this root. For a given + * eb, the lockdep key is determined by the btrfs_root it belongs to and + * the level the eb occupies in the tree. + * + * Different roots are used for different purposes and may nest inside each + * other and they require separate keysets. As lockdep keys should be + * static, assign keysets according to the purpose of the root as indicated + * by btrfs_root->root_key.objectid. This ensures that all special purpose + * roots have separate keysets. + * + * Lock-nesting across peer nodes is always done with the immediate parent + * node locked thus preventing deadlock. As lockdep doesn't know this, use + * subclass to avoid triggering lockdep warning in such cases. + * + * The key is set by the readpage_end_io_hook after the buffer has passed + * csum validation but before the pages are unlocked. It is also set by + * btrfs_init_new_buffer on freshly allocated blocks. + * + * We also add a check to make sure the highest level of the tree is the + * same as our lockdep setup here. If BTRFS_MAX_LEVEL changes, this code + * needs update as well. + */ +#ifdef CONFIG_DEBUG_LOCK_ALLOC +#if BTRFS_MAX_LEVEL != 8 +#error +#endif + +#define DEFINE_LEVEL(stem, level) \ + .names[level] = "btrfs-" stem "-0" #level, + +#define DEFINE_NAME(stem) \ + DEFINE_LEVEL(stem, 0) \ + DEFINE_LEVEL(stem, 1) \ + DEFINE_LEVEL(stem, 2) \ + DEFINE_LEVEL(stem, 3) \ + DEFINE_LEVEL(stem, 4) \ + DEFINE_LEVEL(stem, 5) \ + DEFINE_LEVEL(stem, 6) \ + DEFINE_LEVEL(stem, 7) + +static struct btrfs_lockdep_keyset { + u64 id; /* root objectid */ + /* Longest entry: btrfs-block-group-00 */ + char names[BTRFS_MAX_LEVEL][24]; + struct lock_class_key keys[BTRFS_MAX_LEVEL]; +} btrfs_lockdep_keysets[] = { + { .id = BTRFS_ROOT_TREE_OBJECTID, DEFINE_NAME("root") }, + { .id = BTRFS_EXTENT_TREE_OBJECTID, DEFINE_NAME("extent") }, + { .id = BTRFS_CHUNK_TREE_OBJECTID, DEFINE_NAME("chunk") }, + { .id = BTRFS_DEV_TREE_OBJECTID, DEFINE_NAME("dev") }, + { .id = BTRFS_CSUM_TREE_OBJECTID, DEFINE_NAME("csum") }, + { .id = BTRFS_QUOTA_TREE_OBJECTID, DEFINE_NAME("quota") }, + { .id = BTRFS_TREE_LOG_OBJECTID, DEFINE_NAME("log") }, + { .id = BTRFS_TREE_RELOC_OBJECTID, DEFINE_NAME("treloc") }, + { .id = BTRFS_DATA_RELOC_TREE_OBJECTID, DEFINE_NAME("dreloc") }, + { .id = BTRFS_UUID_TREE_OBJECTID, DEFINE_NAME("uuid") }, + { .id = BTRFS_FREE_SPACE_TREE_OBJECTID, DEFINE_NAME("free-space") }, + { .id = BTRFS_BLOCK_GROUP_TREE_OBJECTID, DEFINE_NAME("block-group") }, + { .id = 0, DEFINE_NAME("tree") }, +}; + +#undef DEFINE_LEVEL +#undef DEFINE_NAME + +void btrfs_set_buffer_lockdep_class(u64 objectid, struct extent_buffer *eb, int level) +{ + struct btrfs_lockdep_keyset *ks; + + BUG_ON(level >= ARRAY_SIZE(ks->keys)); + + /* Find the matching keyset, id 0 is the default entry */ + for (ks = btrfs_lockdep_keysets; ks->id; ks++) + if (ks->id == objectid) + break; + + lockdep_set_class_and_name(&eb->lock, &ks->keys[level], ks->names[level]); +} + +void btrfs_maybe_reset_lockdep_class(struct btrfs_root *root, struct extent_buffer *eb) +{ + if (test_bit(BTRFS_ROOT_RESET_LOCKDEP_CLASS, &root->state)) + btrfs_set_buffer_lockdep_class(root->root_key.objectid, + eb, btrfs_header_level(eb)); +} + +#endif + +/* + * Extent buffer locking + * ===================== + * + * We use a rw_semaphore for tree locking, and the semantics are exactly the + * same: + * + * - reader/writer exclusion + * - writer/writer exclusion + * - reader/reader sharing + * - try-lock semantics for readers and writers + * + * The rwsem implementation does opportunistic spinning which reduces number of + * times the locking task needs to sleep. + */ + +/* + * __btrfs_tree_read_lock - lock extent buffer for read + * @eb: the eb to be locked + * @nest: the nesting level to be used for lockdep + * + * This takes the read lock on the extent buffer, using the specified nesting + * level for lockdep purposes. + */ +void __btrfs_tree_read_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest) +{ + u64 start_ns = 0; + + if (trace_btrfs_tree_read_lock_enabled()) + start_ns = ktime_get_ns(); + + down_read_nested(&eb->lock, nest); + trace_btrfs_tree_read_lock(eb, start_ns); +} + +void btrfs_tree_read_lock(struct extent_buffer *eb) +{ + __btrfs_tree_read_lock(eb, BTRFS_NESTING_NORMAL); +} + +/* + * Try-lock for read. + * + * Return 1 if the rwlock has been taken, 0 otherwise + */ +int btrfs_try_tree_read_lock(struct extent_buffer *eb) +{ + if (down_read_trylock(&eb->lock)) { + trace_btrfs_try_tree_read_lock(eb); + return 1; + } + return 0; +} + +/* + * Try-lock for write. + * + * Return 1 if the rwlock has been taken, 0 otherwise + */ +int btrfs_try_tree_write_lock(struct extent_buffer *eb) +{ + if (down_write_trylock(&eb->lock)) { + eb->lock_owner = current->pid; + trace_btrfs_try_tree_write_lock(eb); + return 1; + } + return 0; +} + +/* + * Release read lock. + */ +void btrfs_tree_read_unlock(struct extent_buffer *eb) +{ + trace_btrfs_tree_read_unlock(eb); + up_read(&eb->lock); +} + +/* + * __btrfs_tree_lock - lock eb for write + * @eb: the eb to lock + * @nest: the nesting to use for the lock + * + * Returns with the eb->lock write locked. + */ +void __btrfs_tree_lock(struct extent_buffer *eb, enum btrfs_lock_nesting nest) + __acquires(&eb->lock) +{ + u64 start_ns = 0; + + if (trace_btrfs_tree_lock_enabled()) + start_ns = ktime_get_ns(); + + down_write_nested(&eb->lock, nest); + eb->lock_owner = current->pid; + trace_btrfs_tree_lock(eb, start_ns); +} + +void btrfs_tree_lock(struct extent_buffer *eb) +{ + __btrfs_tree_lock(eb, BTRFS_NESTING_NORMAL); +} + +/* + * Release the write lock. + */ +void btrfs_tree_unlock(struct extent_buffer *eb) +{ + trace_btrfs_tree_unlock(eb); + eb->lock_owner = 0; + up_write(&eb->lock); +} + +/* + * This releases any locks held in the path starting at level and going all the + * way up to the root. + * + * btrfs_search_slot will keep the lock held on higher nodes in a few corner + * cases, such as COW of the block at slot zero in the node. This ignores + * those rules, and it should only be called when there are no more updates to + * be done higher up in the tree. + */ +void btrfs_unlock_up_safe(struct btrfs_path *path, int level) +{ + int i; + + if (path->keep_locks) + return; + + for (i = level; i < BTRFS_MAX_LEVEL; i++) { + if (!path->nodes[i]) + continue; + if (!path->locks[i]) + continue; + btrfs_tree_unlock_rw(path->nodes[i], path->locks[i]); + path->locks[i] = 0; + } +} + +/* + * Loop around taking references on and locking the root node of the tree until + * we end up with a lock on the root node. + * + * Return: root extent buffer with write lock held + */ +struct extent_buffer *btrfs_lock_root_node(struct btrfs_root *root) +{ + struct extent_buffer *eb; + + while (1) { + eb = btrfs_root_node(root); + + btrfs_maybe_reset_lockdep_class(root, eb); + btrfs_tree_lock(eb); + if (eb == root->node) + break; + btrfs_tree_unlock(eb); + free_extent_buffer(eb); + } + return eb; +} + +/* + * Loop around taking references on and locking the root node of the tree until + * we end up with a lock on the root node. + * + * Return: root extent buffer with read lock held + */ +struct extent_buffer *btrfs_read_lock_root_node(struct btrfs_root *root) +{ + struct extent_buffer *eb; + + while (1) { + eb = btrfs_root_node(root); + + btrfs_maybe_reset_lockdep_class(root, eb); + btrfs_tree_read_lock(eb); + if (eb == root->node) + break; + btrfs_tree_read_unlock(eb); + free_extent_buffer(eb); + } + return eb; +} + +/* + * Loop around taking references on and locking the root node of the tree in + * nowait mode until we end up with a lock on the root node or returning to + * avoid blocking. + * + * Return: root extent buffer with read lock held or -EAGAIN. + */ +struct extent_buffer *btrfs_try_read_lock_root_node(struct btrfs_root *root) +{ + struct extent_buffer *eb; + + while (1) { + eb = btrfs_root_node(root); + if (!btrfs_try_tree_read_lock(eb)) { + free_extent_buffer(eb); + return ERR_PTR(-EAGAIN); + } + if (eb == root->node) + break; + btrfs_tree_read_unlock(eb); + free_extent_buffer(eb); + } + return eb; +} + +/* + * DREW locks + * ========== + * + * DREW stands for double-reader-writer-exclusion lock. It's used in situation + * where you want to provide A-B exclusion but not AA or BB. + * + * Currently implementation gives more priority to reader. If a reader and a + * writer both race to acquire their respective sides of the lock the writer + * would yield its lock as soon as it detects a concurrent reader. Additionally + * if there are pending readers no new writers would be allowed to come in and + * acquire the lock. + */ + +int btrfs_drew_lock_init(struct btrfs_drew_lock *lock) +{ + int ret; + + ret = percpu_counter_init(&lock->writers, 0, GFP_KERNEL); + if (ret) + return ret; + + atomic_set(&lock->readers, 0); + init_waitqueue_head(&lock->pending_readers); + init_waitqueue_head(&lock->pending_writers); + + return 0; +} + +void btrfs_drew_lock_destroy(struct btrfs_drew_lock *lock) +{ + percpu_counter_destroy(&lock->writers); +} + +/* Return true if acquisition is successful, false otherwise */ +bool btrfs_drew_try_write_lock(struct btrfs_drew_lock *lock) +{ + if (atomic_read(&lock->readers)) + return false; + + percpu_counter_inc(&lock->writers); + + /* Ensure writers count is updated before we check for pending readers */ + smp_mb(); + if (atomic_read(&lock->readers)) { + btrfs_drew_write_unlock(lock); + return false; + } + + return true; +} + +void btrfs_drew_write_lock(struct btrfs_drew_lock *lock) +{ + while (true) { + if (btrfs_drew_try_write_lock(lock)) + return; + wait_event(lock->pending_writers, !atomic_read(&lock->readers)); + } +} + +void btrfs_drew_write_unlock(struct btrfs_drew_lock *lock) +{ + percpu_counter_dec(&lock->writers); + cond_wake_up(&lock->pending_readers); +} + +void btrfs_drew_read_lock(struct btrfs_drew_lock *lock) +{ + atomic_inc(&lock->readers); + + /* + * Ensure the pending reader count is perceieved BEFORE this reader + * goes to sleep in case of active writers. This guarantees new writers + * won't be allowed and that the current reader will be woken up when + * the last active writer finishes its jobs. + */ + smp_mb__after_atomic(); + + wait_event(lock->pending_readers, + percpu_counter_sum(&lock->writers) == 0); +} + +void btrfs_drew_read_unlock(struct btrfs_drew_lock *lock) +{ + /* + * atomic_dec_and_test implies a full barrier, so woken up writers + * are guaranteed to see the decrement + */ + if (atomic_dec_and_test(&lock->readers)) + wake_up(&lock->pending_writers); +} -- cgit v1.2.3