diff options
author | Chris Mason <clm@fb.com> | 2014-11-19 10:25:09 -0800 |
---|---|---|
committer | Chris Mason <clm@fb.com> | 2014-11-19 10:34:35 -0800 |
commit | f82c458a2c3ffb94b431fc6ad791a79df1b3713e (patch) | |
tree | 0eca3f95f74d1cde140366002b3cd794ce96f67c /fs/btrfs | |
parent | 6e5aafb27419f32575b27ef9d6a31e5d54661aca (diff) | |
download | op-kernel-dev-f82c458a2c3ffb94b431fc6ad791a79df1b3713e.zip op-kernel-dev-f82c458a2c3ffb94b431fc6ad791a79df1b3713e.tar.gz |
btrfs: fix lockups from btrfs_clear_path_blocking
The fair reader/writer locks mean that btrfs_clear_path_blocking needs
to strictly follow lock ordering rules even when we already have
blocking locks on a given path.
Before we can clear a blocking lock on the path, we need to make sure
all of the locks have been converted to blocking. This will remove lock
inversions against anyone spinning in write_lock() against the buffers
we're trying to get read locks on. These inversions didn't exist before
the fair read/writer locks, but now we need to be more careful.
We papered over this deadlock in the past by changing
btrfs_try_read_lock() to be a true trylock against both the spinlock and
the blocking lock. This was slower, and not sufficient to fix all the
deadlocks. This patch adds a btrfs_tree_read_lock_atomic(), which
basically means get the spinlock but trylock on the blocking lock.
Signed-off-by: Chris Mason <clm@fb.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>
Reported-by: Patrick Schmid <schmid@phys.ethz.ch>
cc: stable@vger.kernel.org #v3.15+
Diffstat (limited to 'fs/btrfs')
-rw-r--r-- | fs/btrfs/ctree.c | 14 | ||||
-rw-r--r-- | fs/btrfs/locking.c | 24 | ||||
-rw-r--r-- | fs/btrfs/locking.h | 2 |
3 files changed, 25 insertions, 15 deletions
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index 19bc616..150822e 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -80,13 +80,6 @@ noinline void btrfs_clear_path_blocking(struct btrfs_path *p, { int i; -#ifdef CONFIG_DEBUG_LOCK_ALLOC - /* lockdep really cares that we take all of these spinlocks - * in the right order. If any of the locks in the path are not - * currently blocking, it is going to complain. So, make really - * really sure by forcing the path to blocking before we clear - * the path blocking. - */ if (held) { btrfs_set_lock_blocking_rw(held, held_rw); if (held_rw == BTRFS_WRITE_LOCK) @@ -95,7 +88,6 @@ noinline void btrfs_clear_path_blocking(struct btrfs_path *p, held_rw = BTRFS_READ_LOCK_BLOCKING; } btrfs_set_path_blocking(p); -#endif for (i = BTRFS_MAX_LEVEL - 1; i >= 0; i--) { if (p->nodes[i] && p->locks[i]) { @@ -107,10 +99,8 @@ noinline void btrfs_clear_path_blocking(struct btrfs_path *p, } } -#ifdef CONFIG_DEBUG_LOCK_ALLOC if (held) btrfs_clear_lock_blocking_rw(held, held_rw); -#endif } /* this also releases the path */ @@ -2893,7 +2883,7 @@ cow_done: } p->locks[level] = BTRFS_WRITE_LOCK; } else { - err = btrfs_try_tree_read_lock(b); + err = btrfs_tree_read_lock_atomic(b); if (!err) { btrfs_set_path_blocking(p); btrfs_tree_read_lock(b); @@ -3025,7 +3015,7 @@ again: } level = btrfs_header_level(b); - err = btrfs_try_tree_read_lock(b); + err = btrfs_tree_read_lock_atomic(b); if (!err) { btrfs_set_path_blocking(p); btrfs_tree_read_lock(b); diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c index 5665d21..f8229ef 100644 --- a/fs/btrfs/locking.c +++ b/fs/btrfs/locking.c @@ -128,6 +128,26 @@ again: } /* + * take a spinning read lock. + * returns 1 if we get the read lock and 0 if we don't + * this won't wait for blocking writers + */ +int btrfs_tree_read_lock_atomic(struct extent_buffer *eb) +{ + if (atomic_read(&eb->blocking_writers)) + return 0; + + read_lock(&eb->lock); + if (atomic_read(&eb->blocking_writers)) { + read_unlock(&eb->lock); + return 0; + } + atomic_inc(&eb->read_locks); + atomic_inc(&eb->spinning_readers); + return 1; +} + +/* * returns 1 if we get the read lock and 0 if we don't * this won't wait for blocking writers */ @@ -158,9 +178,7 @@ int btrfs_try_tree_write_lock(struct extent_buffer *eb) atomic_read(&eb->blocking_readers)) return 0; - if (!write_trylock(&eb->lock)) - return 0; - + write_lock(&eb->lock); if (atomic_read(&eb->blocking_writers) || atomic_read(&eb->blocking_readers)) { write_unlock(&eb->lock); diff --git a/fs/btrfs/locking.h b/fs/btrfs/locking.h index b81e0e9..c44a9d5 100644 --- a/fs/btrfs/locking.h +++ b/fs/btrfs/locking.h @@ -35,6 +35,8 @@ void btrfs_clear_lock_blocking_rw(struct extent_buffer *eb, int rw); void btrfs_assert_tree_locked(struct extent_buffer *eb); int btrfs_try_tree_read_lock(struct extent_buffer *eb); int btrfs_try_tree_write_lock(struct extent_buffer *eb); +int btrfs_tree_read_lock_atomic(struct extent_buffer *eb); + static inline void btrfs_tree_unlock_rw(struct extent_buffer *eb, int rw) { |