The following commit has been merged into the locking/core branch of tip:
Commit-ID: bff7c57c2f50dca7b5e320f499e0898c3fb8a9ff
Gitweb: https://git.kernel.org/tip/bff7c57c2f50dca7b5e320f499e0898c3fb8a9ff
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 23 Sep 2021 14:11:04 -03:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 07 Oct 2021 13:51:11 +02:00
futex: Simplify double_lock_hb()
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@xxxxxxxxxxxxx>
Signed-off-by: André Almeida <andrealmeid@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: André Almeida <andrealmeid@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210923171111.300673-16-andrealmeid@xxxxxxxxxxxxx
---
kernel/futex/futex.h | 14 ++++++--------
1 file changed, 6 insertions(+), 8 deletions(-)
diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
index fe847f5..465f7bd 100644
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -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
|