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futex: Simplify double_lock_hb()

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We need to make sure that all requeue operations take the hash bucket
locks in the same order to avoid deadlock. Simplify the current
double_lock_hb implementation by making sure hb1 is always the
"smallest" bucket to avoid extra checks.

[André: Add commit description]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: André Almeida <andrealmeid@collabora.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: André Almeida <andrealmeid@collabora.com>
Link: https://lore.kernel.org/r/20210923171111.300673-16-andrealmeid@collabora.com
This commit is contained in:
Peter Zijlstra 2021-09-23 14:11:04 -03:00
parent a046f1a0d3
commit bff7c57c2f
1 changed files with 6 additions and 8 deletions
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14
kernel/futex/futex.h
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@ -239,14 +239,12 @@ extern int fixup_pi_owner(u32 __user *uaddr, struct futex_q *q, int locked);
static inline void
double_lock_hb(struct futex_hash_bucket *hb1, struct futex_hash_bucket *hb2)
{
if (hb1 <= hb2) {
spin_lock(&hb1->lock);
if (hb1 < hb2)
spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
} else { /* hb1 > hb2 */
spin_lock(&hb2->lock);
spin_lock_nested(&hb1->lock, SINGLE_DEPTH_NESTING);
}
if (hb1 > hb2)
swap(hb1, hb2);
spin_lock(&hb1->lock);
if (hb1 != hb2)
spin_lock_nested(&hb2->lock, SINGLE_DEPTH_NESTING);
}
static inline void