From 40d38f53d476238594c24c677593913695e6dec7 Mon Sep 17 00:00:00 2001 From: David Sterba Date: Thu, 10 Oct 2019 23:31:19 +0200 Subject: 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 61: retq - 62: lock incl 0x44(%rdi) - 66: add $0x50,%rdi - 6a: jmpq 6f + 62: movl $0x1,0x44(%rdi) + 69: add $0x50,%rdi + 6d: jmpq 72 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 --- fs/btrfs/locking.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'fs') 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 -- cgit v1.2.3