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sbitmap: use test_and_set_bit_lock()/clear_bit_unlock()

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sbitmap_queue_get()/sbitmap_queue_clear() are used for
allocating/freeing a resource, so they should provide acquire/release
barrier semantics, respectively. sbitmap_get() currently contains a full
barrier, which is unnecessary, so use test_and_set_bit_lock() instead of
test_and_set_bit() (these are equivalent on x86_64). sbitmap_clear_bit()
does not imply any barriers, which is incorrect, as accesses of the
resource (e.g., request) could potentially get reordered to after the
clear_bit(). Introduce sbitmap_clear_bit_unlock() and use it for
sbitmap_queue_clear() (this only adds a compiler barrier on x86_64). The
other existing user of sbitmap_clear_bit() (the blk-mq software queue
pending map) is serialized through a spinlock and does not need this.

Reported-by: Tejun Heo <tj@kernel.org>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Omar Sandoval 2018-02-27 16:56:43 -08:00 • committed by Jens Axboe
parent e9a99a6388
commit 4ace53f1ed
2 changed files with 13 additions and 5 deletions
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8
include/linux/sbitmap.h
View file

@ -171,6 +171,8 @@ void sbitmap_resize(struct sbitmap *sb, unsigned int depth);
* starting from the last allocated bit. This is less efficient
* than the default behavior (false).
*
* This operation provides acquire barrier semantics if it succeeds.
*
* Return: Non-negative allocated bit number if successful, -1 otherwise.
*/
int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin);
@ -300,6 +302,12 @@ static inline void sbitmap_clear_bit(struct sbitmap *sb, unsigned int bitnr)
clear_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
}
static inline void sbitmap_clear_bit_unlock(struct sbitmap *sb,
unsigned int bitnr)
{
clear_bit_unlock(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));
}
static inline int sbitmap_test_bit(struct sbitmap *sb, unsigned int bitnr)
{
return test_bit(SB_NR_TO_BIT(sb, bitnr), __sbitmap_word(sb, bitnr));