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From: "tip-bot2 for Peter Zijlstra" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>,
	andrealmeid@collabora.com, x86@kernel.org,
	linux-kernel@vger.kernel.org
Subject: [tip: locking/core] futex: Simplify double_lock_hb()
Date: Sat, 09 Oct 2021 10:07:05 -0000	[thread overview]
Message-ID: <163377402559.25758.4094406809962751599.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20210923171111.300673-16-andrealmeid@collabora.com>

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@infradead.org>
AuthorDate:    Thu, 23 Sep 2021 14:11:04 -03:00
Committer:     Peter Zijlstra <peterz@infradead.org>
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@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
---
 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

  reply	other threads:[~2021-10-09 10:07 UTC|newest]

Thread overview: 56+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-23 17:10 [PATCH v2 00/22] futex: splitup and waitv syscall André Almeida
2021-09-23 17:10 ` [PATCH v2 01/22] futex: Move to kernel/futex/ André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-10-09 14:23     ` André Almeida
2021-10-09 15:56       ` Peter Zijlstra
2021-09-23 17:10 ` [PATCH v2 02/22] futex: Split out syscalls André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-09-23 17:10 ` [PATCH v2 03/22] futex: Rename {,__}{,un}queue_me() André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-09-23 17:10 ` [PATCH v2 04/22] futex: Rename futex_wait_queue_me() André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-09-23 17:10 ` [PATCH v2 05/22] futex: Rename: queue_{,un}lock() André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-09-23 17:10 ` [PATCH v2 06/22] futex: Rename __unqueue_futex() André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-09-23 17:10 ` [PATCH v2 07/22] futex: Rename hash_futex() André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-09-23 17:10 ` [PATCH v2 08/22] futex: Rename: {get,cmpxchg}_futex_value_locked() André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-09-23 17:10 ` [PATCH v2 09/22] futex: Split out PI futex André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-09-23 17:10 ` [PATCH v2 10/22] futex: Rename: hb_waiter_{inc,dec,pending}() André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-09-23 17:11 ` [PATCH v2 11/22] futex: Rename: match_futex() André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-09-23 17:11 ` [PATCH v2 12/22] futex: Rename mark_wake_futex() André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-09-23 17:11 ` [PATCH v2 13/22] futex: Split out requeue André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-10-13 16:57     ` Mike Galbraith
2021-10-15 10:01       ` Peter Zijlstra
2021-09-23 17:11 ` [PATCH v2 14/22] futex: Split out wait/wake André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for Peter Zijlstra
2021-09-23 17:11 ` [PATCH v2 15/22] futex: Simplify double_lock_hb() André Almeida
2021-10-09 10:07   ` tip-bot2 for Peter Zijlstra [this message]
2021-09-23 17:11 ` [PATCH v2 16/22] futex: Implement sys_futex_waitv() André Almeida
2021-10-06 11:50   ` Peter Zijlstra
     [not found]     ` <47b13460-27a4-474c-879b-ed1c668e5923@www.fastmail.com>
2021-10-07  9:08       ` Peter Zijlstra
2021-10-07 13:27         ` Steven Rostedt
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for André Almeida
2021-09-23 17:11 ` [PATCH v2 17/22] futex,x86: Wire up sys_futex_waitv() André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for André Almeida
2021-09-23 17:11 ` [PATCH v2 18/22] futex,arm: " André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for André Almeida
2021-09-23 17:11 ` [PATCH v2 19/22] selftests: futex: Add sys_futex_waitv() test André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for André Almeida
2021-09-23 17:11 ` [PATCH v2 20/22] selftests: futex: Test sys_futex_waitv() timeout André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for André Almeida
2021-11-09 11:18   ` [PATCH v2 20/22] " Vasily Gorbik
2021-11-09 12:52     ` André Almeida
2021-11-09 13:00       ` Adhemerval Zanella
2021-11-09 13:05       ` Arnd Bergmann
2021-09-23 17:11 ` [PATCH v2 21/22] selftests: futex: Test sys_futex_waitv() wouldblock André Almeida
2021-10-09 10:07   ` [tip: locking/core] " tip-bot2 for André Almeida
2021-09-23 17:11 ` [PATCH v2 22/22] futex2: Documentation: Document sys_futex_waitv() uAPI André Almeida
2021-10-09 10:06   ` [tip: locking/core] " tip-bot2 for André Almeida

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