diff options
author | Linus Torvalds <torvalds@linux-foundation.org> | 2011-07-27 16:43:52 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2011-07-27 16:43:52 -0700 |
commit | 22712200e175e0df5c7f9edfe6c6bf5c94c23b83 (patch) | |
tree | a3e332aab7f5a953ff4f12e67af2a0e5f32f5be5 /fs/btrfs/locking.c | |
parent | 597a67e0ba758e3d2239c81fbb648c6e69ec30a2 (diff) | |
parent | ff95acb6733d41a8d45feb0e18b96df25e610e78 (diff) |
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/btrfs-unstable:
Btrfs: make sure reserve_metadata_bytes doesn't leak out strange errors
Btrfs: use the commit_root for reading free_space_inode crcs
Btrfs: reduce extent_state lock contention for metadata
Btrfs: remove lockdep magic from btrfs_next_leaf
Btrfs: make a lockdep class for each root
Btrfs: switch the btrfs tree locks to reader/writer
Btrfs: fix deadlock when throttling transactions
Btrfs: stop using highmem for extent_buffers
Btrfs: fix BUG_ON() caused by ENOSPC when relocating space
Btrfs: tag pages for writeback in sync
Btrfs: fix enospc problems with delalloc
Btrfs: don't flush delalloc arbitrarily
Btrfs: use find_or_create_page instead of grab_cache_page
Btrfs: use a worker thread to do caching
Btrfs: fix how we merge extent states and deal with cached states
Btrfs: use the normal checksumming infrastructure for free space cache
Btrfs: serialize flushers in reserve_metadata_bytes
Btrfs: do transaction space reservation before joining the transaction
Btrfs: try to only do one btrfs_search_slot in do_setxattr
Diffstat (limited to 'fs/btrfs/locking.c')
-rw-r--r-- | fs/btrfs/locking.c | 280 |
1 files changed, 146 insertions, 134 deletions
diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c index 66fa43dc3f0..d77b67c4b27 100644 --- a/fs/btrfs/locking.c +++ b/fs/btrfs/locking.c @@ -24,185 +24,197 @@ #include "extent_io.h" #include "locking.h" -static inline void spin_nested(struct extent_buffer *eb) -{ - spin_lock(&eb->lock); -} +void btrfs_assert_tree_read_locked(struct extent_buffer *eb); /* - * Setting a lock to blocking will drop the spinlock and set the - * flag that forces other procs who want the lock to wait. After - * this you can safely schedule with the lock held. + * if we currently have a spinning reader or writer lock + * (indicated by the rw flag) this will bump the count + * of blocking holders and drop the spinlock. */ -void btrfs_set_lock_blocking(struct extent_buffer *eb) +void btrfs_set_lock_blocking_rw(struct extent_buffer *eb, int rw) { - if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) { - set_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags); - spin_unlock(&eb->lock); + if (rw == BTRFS_WRITE_LOCK) { + if (atomic_read(&eb->blocking_writers) == 0) { + WARN_ON(atomic_read(&eb->spinning_writers) != 1); + atomic_dec(&eb->spinning_writers); + btrfs_assert_tree_locked(eb); + atomic_inc(&eb->blocking_writers); + write_unlock(&eb->lock); + } + } else if (rw == BTRFS_READ_LOCK) { + btrfs_assert_tree_read_locked(eb); + atomic_inc(&eb->blocking_readers); + WARN_ON(atomic_read(&eb->spinning_readers) == 0); + atomic_dec(&eb->spinning_readers); + read_unlock(&eb->lock); } - /* exit with the spin lock released and the bit set */ + return; } /* - * clearing the blocking flag will take the spinlock again. - * After this you can't safely schedule + * if we currently have a blocking lock, take the spinlock + * and drop our blocking count */ -void btrfs_clear_lock_blocking(struct extent_buffer *eb) +void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw) { - if (test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) { - spin_nested(eb); - clear_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags); - smp_mb__after_clear_bit(); + if (rw == BTRFS_WRITE_LOCK_BLOCKING) { + BUG_ON(atomic_read(&eb->blocking_writers) != 1); + write_lock(&eb->lock); + WARN_ON(atomic_read(&eb->spinning_writers)); + atomic_inc(&eb->spinning_writers); + if (atomic_dec_and_test(&eb->blocking_writers)) + wake_up(&eb->write_lock_wq); + } else if (rw == BTRFS_READ_LOCK_BLOCKING) { + BUG_ON(atomic_read(&eb->blocking_readers) == 0); + read_lock(&eb->lock); + atomic_inc(&eb->spinning_readers); + if (atomic_dec_and_test(&eb->blocking_readers)) + wake_up(&eb->read_lock_wq); } - /* exit with the spin lock held */ + return; } /* - * unfortunately, many of the places that currently set a lock to blocking - * don't end up blocking for very long, and often they don't block - * at all. For a dbench 50 run, if we don't spin on the blocking bit - * at all, the context switch rate can jump up to 400,000/sec or more. - * - * So, we're still stuck with this crummy spin on the blocking bit, - * at least until the most common causes of the short blocks - * can be dealt with. + * take a spinning read lock. This will wait for any blocking + * writers */ -static int btrfs_spin_on_block(struct extent_buffer *eb) +void btrfs_tree_read_lock(struct extent_buffer *eb) { - int i; - - for (i = 0; i < 512; i++) { - if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) - return 1; - if (need_resched()) - break; - cpu_relax(); +again: + wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0); + read_lock(&eb->lock); + if (atomic_read(&eb->blocking_writers)) { + read_unlock(&eb->lock); + wait_event(eb->write_lock_wq, + atomic_read(&eb->blocking_writers) == 0); + goto again; } - return 0; + atomic_inc(&eb->read_locks); + atomic_inc(&eb->spinning_readers); } /* - * This is somewhat different from trylock. It will take the - * spinlock but if it finds the lock is set to blocking, it will - * return without the lock held. - * - * returns 1 if it was able to take the lock and zero otherwise - * - * After this call, scheduling is not safe without first calling - * btrfs_set_lock_blocking() + * returns 1 if we get the read lock and 0 if we don't + * this won't wait for blocking writers */ -int btrfs_try_spin_lock(struct extent_buffer *eb) +int btrfs_try_tree_read_lock(struct extent_buffer *eb) { - int i; + if (atomic_read(&eb->blocking_writers)) + return 0; - if (btrfs_spin_on_block(eb)) { - spin_nested(eb); - if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) - return 1; - spin_unlock(&eb->lock); + read_lock(&eb->lock); + if (atomic_read(&eb->blocking_writers)) { + read_unlock(&eb->lock); + return 0; } - /* spin for a bit on the BLOCKING flag */ - for (i = 0; i < 2; i++) { - cpu_relax(); - if (!btrfs_spin_on_block(eb)) - break; - - spin_nested(eb); - if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) - return 1; - spin_unlock(&eb->lock); - } - return 0; + atomic_inc(&eb->read_locks); + atomic_inc(&eb->spinning_readers); + return 1; } /* - * the autoremove wake function will return 0 if it tried to wake up - * a process that was already awake, which means that process won't - * count as an exclusive wakeup. The waitq code will continue waking - * procs until it finds one that was actually sleeping. - * - * For btrfs, this isn't quite what we want. We want a single proc - * to be notified that the lock is ready for taking. If that proc - * already happen to be awake, great, it will loop around and try for - * the lock. - * - * So, btrfs_wake_function always returns 1, even when the proc that we - * tried to wake up was already awake. + * returns 1 if we get the read lock and 0 if we don't + * this won't wait for blocking writers or readers */ -static int btrfs_wake_function(wait_queue_t *wait, unsigned mode, - int sync, void *key) +int btrfs_try_tree_write_lock(struct extent_buffer *eb) { - autoremove_wake_function(wait, mode, sync, key); + if (atomic_read(&eb->blocking_writers) || + atomic_read(&eb->blocking_readers)) + return 0; + write_lock(&eb->lock); + if (atomic_read(&eb->blocking_writers) || + atomic_read(&eb->blocking_readers)) { + write_unlock(&eb->lock); + return 0; + } + atomic_inc(&eb->write_locks); + atomic_inc(&eb->spinning_writers); return 1; } /* - * returns with the extent buffer spinlocked. - * - * This will spin and/or wait as required to take the lock, and then - * return with the spinlock held. - * - * After this call, scheduling is not safe without first calling - * btrfs_set_lock_blocking() + * drop a spinning read lock + */ +void btrfs_tree_read_unlock(struct extent_buffer *eb) +{ + btrfs_assert_tree_read_locked(eb); + WARN_ON(atomic_read(&eb->spinning_readers) == 0); + atomic_dec(&eb->spinning_readers); + atomic_dec(&eb->read_locks); + read_unlock(&eb->lock); +} + +/* + * drop a blocking read lock + */ +void btrfs_tree_read_unlock_blocking(struct extent_buffer *eb) +{ + btrfs_assert_tree_read_locked(eb); + WARN_ON(atomic_read(&eb->blocking_readers) == 0); + if (atomic_dec_and_test(&eb->blocking_readers)) + wake_up(&eb->read_lock_wq); + atomic_dec(&eb->read_locks); +} + +/* + * take a spinning write lock. This will wait for both + * blocking readers or writers */ int btrfs_tree_lock(struct extent_buffer *eb) { - DEFINE_WAIT(wait); - wait.func = btrfs_wake_function; - - if (!btrfs_spin_on_block(eb)) - goto sleep; - - while(1) { - spin_nested(eb); - - /* nobody is blocking, exit with the spinlock held */ - if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) - return 0; - - /* - * we have the spinlock, but the real owner is blocking. - * wait for them - */ - spin_unlock(&eb->lock); - - /* - * spin for a bit, and if the blocking flag goes away, - * loop around - */ - cpu_relax(); - if (btrfs_spin_on_block(eb)) - continue; -sleep: - prepare_to_wait_exclusive(&eb->lock_wq, &wait, - TASK_UNINTERRUPTIBLE); - - if (test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) - schedule(); - - finish_wait(&eb->lock_wq, &wait); +again: + wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0); + wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0); + write_lock(&eb->lock); + if (atomic_read(&eb->blocking_readers)) { + write_unlock(&eb->lock); + wait_event(eb->read_lock_wq, + atomic_read(&eb->blocking_readers) == 0); + goto again; } + if (atomic_read(&eb->blocking_writers)) { + write_unlock(&eb->lock); + wait_event(eb->write_lock_wq, + atomic_read(&eb->blocking_writers) == 0); + goto again; + } + WARN_ON(atomic_read(&eb->spinning_writers)); + atomic_inc(&eb->spinning_writers); + atomic_inc(&eb->write_locks); return 0; } +/* + * drop a spinning or a blocking write lock. + */ int btrfs_tree_unlock(struct extent_buffer *eb) { - /* - * if we were a blocking owner, we don't have the spinlock held - * just clear the bit and look for waiters - */ - if (test_and_clear_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) - smp_mb__after_clear_bit(); - else - spin_unlock(&eb->lock); - - if (waitqueue_active(&eb->lock_wq)) - wake_up(&eb->lock_wq); + int blockers = atomic_read(&eb->blocking_writers); + + BUG_ON(blockers > 1); + + btrfs_assert_tree_locked(eb); + atomic_dec(&eb->write_locks); + + if (blockers) { + WARN_ON(atomic_read(&eb->spinning_writers)); + atomic_dec(&eb->blocking_writers); + smp_wmb(); + wake_up(&eb->write_lock_wq); + } else { + WARN_ON(atomic_read(&eb->spinning_writers) != 1); + atomic_dec(&eb->spinning_writers); + write_unlock(&eb->lock); + } return 0; } void btrfs_assert_tree_locked(struct extent_buffer *eb) { - if (!test_bit(EXTENT_BUFFER_BLOCKING, &eb->bflags)) - assert_spin_locked(&eb->lock); + BUG_ON(!atomic_read(&eb->write_locks)); +} + +void btrfs_assert_tree_read_locked(struct extent_buffer *eb) +{ + BUG_ON(!atomic_read(&eb->read_locks)); } |