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| author | David Sterba <dsterba@suse.com> | 2019-10-10 23:31:19 +0200 |
|---|---|---|
| committer | David Sterba <dsterba@suse.com> | 2019-11-18 17:51:50 +0100 |
| commit | 40d38f53d476238594c24c677593913695e6dec7 (patch) | |
| tree | 3042c9176b8e9f2d085e71964b47647053b91da1 | |
| parent | f5c2a52590858d18f4a736d8062fe70f11988fa9 (diff) | |
| download | linux-40d38f53d476238594c24c677593913695e6dec7.tar.bz2 | |
btrfs: set blocking_writers directly, no increment or decrement
The increment and decrement was inherited from previous version that
used atomics, switched in commit 06297d8cefca ("btrfs: switch
extent_buffer blocking_writers from atomic to int"). The only possible
values are 0 and 1 so we can set them directly.
The generated assembly (gcc 9.x) did the direct value assignment in
btrfs_set_lock_blocking_write (asm diff after change in 06297d8cefca):
5d: test %eax,%eax
5f: je 62 <btrfs_set_lock_blocking_write+0x22>
61: retq
- 62: lock incl 0x44(%rdi)
- 66: add $0x50,%rdi
- 6a: jmpq 6f <btrfs_set_lock_blocking_write+0x2f>
+ 62: movl $0x1,0x44(%rdi)
+ 69: add $0x50,%rdi
+ 6d: jmpq 72 <btrfs_set_lock_blocking_write+0x32>
The part in btrfs_tree_unlock did a decrement because
BUG_ON(blockers > 1) is probably not a strong hint for the compiler, but
otherwise the output looks safe:
- lock decl 0x44(%rdi)
+ sub $0x1,%eax
+ mov %eax,0x44(%rdi)
Signed-off-by: David Sterba <dsterba@suse.com>
| -rw-r--r-- | fs/btrfs/locking.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c index c84c650e56c7..00edf91c3d1c 100644 --- a/fs/btrfs/locking.c +++ b/fs/btrfs/locking.c @@ -109,7 +109,7 @@ void btrfs_set_lock_blocking_write(struct extent_buffer *eb) if (eb->blocking_writers == 0) { btrfs_assert_spinning_writers_put(eb); btrfs_assert_tree_locked(eb); - eb->blocking_writers++; + eb->blocking_writers = 1; write_unlock(&eb->lock); } } @@ -305,7 +305,7 @@ void btrfs_tree_unlock(struct extent_buffer *eb) if (blockers) { btrfs_assert_no_spinning_writers(eb); - eb->blocking_writers--; + eb->blocking_writers = 0; /* * We need to order modifying blocking_writers above with * actually waking up the sleepers to ensure they see the |