From nobody Wed Dec 17 13:54:12 2025 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CAB821A8F84; Mon, 17 Mar 2025 16:40:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742229618; cv=none; b=nTFFuhiFoxE/LSds68VPfcpfw05ccQUimSYpXMJgrrkUnEIPgsAYBip5wPpMce9VElI79ByuACPSP3LDhvoZe6Kh+rrpMZQqHzVAPZsZns/fCbvkBQzSs+Kk9fivRAd1vCyq5jN1rq3Dd/Ir3DskppImVyVm5ylouokFE572fIo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742229618; c=relaxed/simple; bh=KPqq7IKw/v0+vm2iRgZpMnlwStLutH2yikFw0m6VI0U=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=Q1kH9uN+7XZaXNVf92QWqF8pvydWDLRugBgGraZYKH3Sg3343ja3dOIYEHvVSfRKnRuuaqe6VYnE+DzbSjoREiZ5fRE77/ZsmJGUouWFfYU3lwSAVVTE13fLdUY0fpi6eGX7O3XSfnpj2r55Z1hbA876myL3A+roKuuDSiJaAWc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PADrlJ+4; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="PADrlJ+4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DF9CAC4CEED; Mon, 17 Mar 2025 16:40:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1742229618; bh=KPqq7IKw/v0+vm2iRgZpMnlwStLutH2yikFw0m6VI0U=; h=From:To:Cc:Subject:Date:From; b=PADrlJ+4YmfIdILFrkMLFE2NFz6SRh8MzAgVMlXAyZs80TTw06RR8woz89TWxDyOW F5/gm7qsISuS9R/qQe7EYIlzF8M5Fnx4YqshDUKpGoQnLEDOS4viOA0AzkIHSTqSpj n4Xyu39Udr0fXJIZoaVZwECugnNABatRob1YrMX0gey6C5QP/FdNIrZUw+TDgzAyl3 Bn96P282qYLPNnicCgztEvIfgryNnNDFQZIm0JC/PCDV7k7NzbKJ14k2KMvHWfj6FZ K/fiI5/FLy13LlvpcE3433DvgqQ9J7WLyQPx7+DdNFcXXbKu/Mo+EiQ72en+ONj4nH s4uUG7onod/cw== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Waiman Long , yzbot+ed801a886dfdbfe7136d@syzkaller.appspotmail.com, Boqun Feng , Ingo Molnar , Linus Torvalds , Sasha Levin , peterz@infradead.org, mingo@redhat.com, will@kernel.org, bigeasy@linutronix.de, clrkwllms@kernel.org, rostedt@goodmis.org, linux-rt-devel@lists.linux.dev Subject: [PATCH AUTOSEL 5.4] locking/semaphore: Use wake_q to wake up processes outside lock critical section Date: Mon, 17 Mar 2025 12:40:15 -0400 Message-Id: <20250317164015.1893964-1-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 5.4.291 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Waiman Long [ Upstream commit 85b2b9c16d053364e2004883140538e73b333cdb ] A circular lock dependency splat has been seen involving down_trylock(): =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D WARNING: possible circular locking dependency detected 6.12.0-41.el10.s390x+debug ------------------------------------------------------ dd/32479 is trying to acquire lock: 0015a20accd0d4f8 ((console_sem).lock){-.-.}-{2:2}, at: down_trylock+0x26/= 0x90 but task is already holding lock: 000000017e461698 (&zone->lock){-.-.}-{2:2}, at: rmqueue_bulk+0xac/0x8f0 the existing dependency chain (in reverse order) is: -> #4 (&zone->lock){-.-.}-{2:2}: -> #3 (hrtimer_bases.lock){-.-.}-{2:2}: -> #2 (&rq->__lock){-.-.}-{2:2}: -> #1 (&p->pi_lock){-.-.}-{2:2}: -> #0 ((console_sem).lock){-.-.}-{2:2}: The console_sem -> pi_lock dependency is due to calling try_to_wake_up() while holding the console_sem raw_spinlock. This dependency can be broken by using wake_q to do the wakeup instead of calling try_to_wake_up() under the console_sem lock. This will also make the semaphore's raw_spinlock become a terminal lock without taking any further locks underneath it. The hrtimer_bases.lock is a raw_spinlock while zone->lock is a spinlock. The hrtimer_bases.lock -> zone->lock dependency happens via the debug_objects_fill_pool() helper function in the debugobjects code. -> #4 (&zone->lock){-.-.}-{2:2}: __lock_acquire+0xe86/0x1cc0 lock_acquire.part.0+0x258/0x630 lock_acquire+0xb8/0xe0 _raw_spin_lock_irqsave+0xb4/0x120 rmqueue_bulk+0xac/0x8f0 __rmqueue_pcplist+0x580/0x830 rmqueue_pcplist+0xfc/0x470 rmqueue.isra.0+0xdec/0x11b0 get_page_from_freelist+0x2ee/0xeb0 __alloc_pages_noprof+0x2c2/0x520 alloc_pages_mpol_noprof+0x1fc/0x4d0 alloc_pages_noprof+0x8c/0xe0 allocate_slab+0x320/0x460 ___slab_alloc+0xa58/0x12b0 __slab_alloc.isra.0+0x42/0x60 kmem_cache_alloc_noprof+0x304/0x350 fill_pool+0xf6/0x450 debug_object_activate+0xfe/0x360 enqueue_hrtimer+0x34/0x190 __run_hrtimer+0x3c8/0x4c0 __hrtimer_run_queues+0x1b2/0x260 hrtimer_interrupt+0x316/0x760 do_IRQ+0x9a/0xe0 do_irq_async+0xf6/0x160 Normally a raw_spinlock to spinlock dependency is not legitimate and will be warned if CONFIG_PROVE_RAW_LOCK_NESTING is enabled, but debug_objects_fill_pool() is an exception as it explicitly allows this dependency for non-PREEMPT_RT kernel without causing PROVE_RAW_LOCK_NESTING lockdep splat. As a result, this dependency is legitimate and not a bug. Anyway, semaphore is the only locking primitive left that is still using try_to_wake_up() to do wakeup inside critical section, all the other locking primitives had been migrated to use wake_q to do wakeup outside of the critical section. It is also possible that there are other circular locking dependencies involving printk/console_sem or other existing/new semaphores lurking somewhere which may show up in the future. Let just do the migration now to wake_q to avoid headache like this. Reported-by: yzbot+ed801a886dfdbfe7136d@syzkaller.appspotmail.com Signed-off-by: Waiman Long Signed-off-by: Boqun Feng Signed-off-by: Ingo Molnar Cc: Linus Torvalds Link: https://lore.kernel.org/r/20250307232717.1759087-3-boqun.feng@gmail.c= om Signed-off-by: Sasha Levin --- kernel/locking/semaphore.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c index d9dd94defc0a9..19389fdbfdfb1 100644 --- a/kernel/locking/semaphore.c +++ b/kernel/locking/semaphore.c @@ -29,6 +29,7 @@ #include #include #include +#include #include #include #include @@ -37,7 +38,7 @@ static noinline void __down(struct semaphore *sem); static noinline int __down_interruptible(struct semaphore *sem); static noinline int __down_killable(struct semaphore *sem); static noinline int __down_timeout(struct semaphore *sem, long timeout); -static noinline void __up(struct semaphore *sem); +static noinline void __up(struct semaphore *sem, struct wake_q_head *wake_= q); =20 /** * down - acquire the semaphore @@ -178,13 +179,16 @@ EXPORT_SYMBOL(down_timeout); void up(struct semaphore *sem) { unsigned long flags; + DEFINE_WAKE_Q(wake_q); =20 raw_spin_lock_irqsave(&sem->lock, flags); if (likely(list_empty(&sem->wait_list))) sem->count++; else - __up(sem); + __up(sem, &wake_q); raw_spin_unlock_irqrestore(&sem->lock, flags); + if (!wake_q_empty(&wake_q)) + wake_up_q(&wake_q); } EXPORT_SYMBOL(up); =20 @@ -252,11 +256,12 @@ static noinline int __sched __down_timeout(struct sem= aphore *sem, long timeout) return __down_common(sem, TASK_UNINTERRUPTIBLE, timeout); } =20 -static noinline void __sched __up(struct semaphore *sem) +static noinline void __sched __up(struct semaphore *sem, + struct wake_q_head *wake_q) { struct semaphore_waiter *waiter =3D list_first_entry(&sem->wait_list, struct semaphore_waiter, list); list_del(&waiter->list); waiter->up =3D true; - wake_up_process(waiter->task); + wake_q_add(wake_q, waiter->task); } --=20 2.39.5