From nobody Fri Dec 19 16:07:06 2025 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 AAD97EEA8 for ; Mon, 27 Jan 2025 01:32:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737941540; cv=none; b=Zp8ZVCwI0OCPkstQDSKa5ww0PVtyfJxZY+aVchaEYoastd/iGsmTyS089M0BTllucBVwuidb1qAWLnsjihgY1SHfwC+K5trftbrLmsLM11W7t3ttf4yiF81bcUEnGAJVe9HOXsQ/B891+XV1KVHXD3dASgZa4xYOOWOFIM83Pqc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737941540; c=relaxed/simple; bh=Ee7TElrTtASQaWzioWueAUtqvk8cLfhqidbWLL+fqJQ=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=Rk7pxJ7axMfjKclRpp3DxwA1cX8Mqjp9P2NvNhpfBDWiinfBzBeiMUIZ1H/S1eopcCRgTq55XguUFLKbL5bBI5uzDLAKC2TabSQdSfELFzbik3QVxWDaB1SxhFp1JkrDJuSDKqHxjQjNloeiUyUk9D/l/gOJTl/GNd2pz9lhlpo= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=X/ooDMnM; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="X/ooDMnM" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1737941537; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=KolE3rv9+SYp644//WabAXp2ydPrtfpM9GvZJWVkVBY=; b=X/ooDMnMf2BnRY1aaK2ti7u/Wat9pH6aOjuylPp+D0+f5GoObbgFRF/3KdIHfGna1PnzJc ciG5nJQSw1tBFqwnuvyrHmLcXbU8tK4kX5qho2HdFBQz9vmXlWliJ/69ME8VwK4iKb/gRB 3ViwZbpKTnDuld9c3JB0V+y/aLP3H9M= Received: from mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-48-SYkszqzRPwCBZsUoE0ZKHg-1; Sun, 26 Jan 2025 20:32:13 -0500 X-MC-Unique: SYkszqzRPwCBZsUoE0ZKHg-1 X-Mimecast-MFC-AGG-ID: SYkszqzRPwCBZsUoE0ZKHg Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 54FF319560BA; Mon, 27 Jan 2025 01:32:12 +0000 (UTC) Received: from llong-thinkpadp16vgen1.westford.csb (unknown [10.22.80.100]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 6E752195608A; Mon, 27 Jan 2025 01:32:10 +0000 (UTC) From: Waiman Long To: Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng Cc: linux-kernel@vger.kernel.org, Waiman Long Subject: [PATCH v3] locking/semaphore: Use wake_q to wake up processes outside lock critical section Date: Sun, 26 Jan 2025 20:31:27 -0500 Message-ID: <20250127013127.3913153-1-longman@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 Content-Type: text/plain; charset="utf-8" A circular lock dependency splat has been seen involving down_trylock(). [ 4011.795602] =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 [ 4011.795603] WARNING: possible circular locking dependency detected [ 4011.795607] 6.12.0-41.el10.s390x+debug [ 4011.795612] ------------------------------------------------------ [ 4011.795613] dd/32479 is trying to acquire lock: [ 4011.795617] 0015a20accd0d4f8 ((console_sem).lock){-.-.}-{2:2}, at: down_= trylock+0x26/0x90 [ 4011.795636] [ 4011.795636] but task is already holding lock: [ 4011.795637] 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. [ 4011.795646] -> #4 (&zone->lock){-.-.}-{2:2}: [ 4011.795650] __lock_acquire+0xe86/0x1cc0 [ 4011.795655] lock_acquire.part.0+0x258/0x630 [ 4011.795657] lock_acquire+0xb8/0xe0 [ 4011.795659] _raw_spin_lock_irqsave+0xb4/0x120 [ 4011.795663] rmqueue_bulk+0xac/0x8f0 [ 4011.795665] __rmqueue_pcplist+0x580/0x830 [ 4011.795667] rmqueue_pcplist+0xfc/0x470 [ 4011.795669] rmqueue.isra.0+0xdec/0x11b0 [ 4011.795671] get_page_from_freelist+0x2ee/0xeb0 [ 4011.795673] __alloc_pages_noprof+0x2c2/0x520 [ 4011.795676] alloc_pages_mpol_noprof+0x1fc/0x4d0 [ 4011.795681] alloc_pages_noprof+0x8c/0xe0 [ 4011.795684] allocate_slab+0x320/0x460 [ 4011.795686] ___slab_alloc+0xa58/0x12b0 [ 4011.795688] __slab_alloc.isra.0+0x42/0x60 [ 4011.795690] kmem_cache_alloc_noprof+0x304/0x350 [ 4011.795692] fill_pool+0xf6/0x450 [ 4011.795697] debug_object_activate+0xfe/0x360 [ 4011.795700] enqueue_hrtimer+0x34/0x190 [ 4011.795703] __run_hrtimer+0x3c8/0x4c0 [ 4011.795705] __hrtimer_run_queues+0x1b2/0x260 [ 4011.795707] hrtimer_interrupt+0x316/0x760 [ 4011.795709] do_IRQ+0x9a/0xe0 [ 4011.795712] do_irq_async+0xf6/0x160 Normally raw_spinlock to spinlock dependency is not legit and will be warned if 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 legit 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. Signed-off-by: Waiman Long Reported-by:syzbot+ed801a886dfdbfe7136d@syzkaller.appspotmail.com --- 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 34bfae72f295..de9117c0e671 100644 --- a/kernel/locking/semaphore.c +++ b/kernel/locking/semaphore.c @@ -29,6 +29,7 @@ #include #include #include +#include #include #include #include @@ -38,7 +39,7 @@ 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 @@ -183,13 +184,16 @@ EXPORT_SYMBOL(down_timeout); void __sched 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 @@ -269,11 +273,12 @@ 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 2.47.1