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authorOmar Sandoval <osandov@fb.com>2018-02-28 03:56:43 +0300
committerJens Axboe <axboe@kernel.dk>2018-02-28 22:23:35 +0300
commit4ace53f1ed40a5cfee4bdd7614c8a8b2798227ad (patch)
treec766967b9ac9c5ae7a04035c0fa182fb27167d33 /include/linux/sbitmap.h
parente9a99a638800af25c7ed006c96fd1dabb99254b7 (diff)
downloadlinux-4ace53f1ed40a5cfee4bdd7614c8a8b2798227ad.tar.xz
sbitmap: use test_and_set_bit_lock()/clear_bit_unlock()
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>
Diffstat (limited to 'include/linux/sbitmap.h')
-rw-r--r--include/linux/sbitmap.h8
1 files changed, 8 insertions, 0 deletions
diff --git a/include/linux/sbitmap.h b/include/linux/sbitmap.h
index 0dcc60e820de..841585f6e5f2 100644
--- a/include/linux/sbitmap.h
+++ b/include/linux/sbitmap.h
@@ -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));