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authorDavid Sterba <dsterba@suse.com>2019-10-10 23:31:19 +0200
committerDavid Sterba <dsterba@suse.com>2019-11-18 17:51:50 +0100
commit40d38f53d476238594c24c677593913695e6dec7 (patch)
tree3042c9176b8e9f2d085e71964b47647053b91da1
parentbtrfs: merge blocking_writers branches in btrfs_tree_read_lock (diff)
downloadlinux-40d38f53d476238594c24c677593913695e6dec7.tar.xz
linux-40d38f53d476238594c24c677593913695e6dec7.zip
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.c4
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