From mboxrd@z Thu Jan 1 00:00:00 1970 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 348FF1D89FA; Mon, 17 Mar 2025 16:39:52 +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=1742229593; cv=none; b=Yn4+zu6l5C1AXXVJfiWG8Qy5SnyUbsRZwRrc75+T/UFj/16UWeky38fgxZtJ808koLZASjmmGJBEg4i/caRJCxPnjqPjcRdgamFTvxkCCjo5ZmFyUQ5cn1OFN4sjCuTzRGyOGajoYuM3eIIdSUboN1k1m0inJKycZRKhcltetGQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742229593; c=relaxed/simple; bh=Ueo8+OP46BR7h+ZjlZaKgwvjpsOiazfbnA/5jazPig8=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=mmi8K+N8vDXN+x5xXLlawuCJi9PweV9xOg4ZzicVqsAsPos6bpFNEQ5w+gZTap+CsTGQsZ5xj4c3NHNuzmek9zvaLCm9Q938EiFwqwjd4zToV+SMT9Z+XnpAZjmDMJ4a8cgmfuYukTDg0FByOj4w545wCrIaCwTo6Tnd2xse5pM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lfgrEpIi; 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="lfgrEpIi" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B293CC4CEF1; Mon, 17 Mar 2025 16:39:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1742229592; bh=Ueo8+OP46BR7h+ZjlZaKgwvjpsOiazfbnA/5jazPig8=; h=From:To:Cc:Subject:Date:From; b=lfgrEpIisp2sJ0cKbeWTZnOPXAytuQl2lHp0HS9xM82q8L9C8mAhEYdqPPaol9gWF G4+oOzIrgdVdyriQO41xcBQT76FpOu7f8n3HF5IIsO4m3x3yGHoy/sPyHODWB2GPyp HNAUZf/fud6ZENNtopnYrD3Ezmt6+LRlLFQndly5vGwaowRlHCMhuyEdbn4TO7T/zC 2rQyQCE3bi+zxns7pyQVAc9YWeQGrUyba+B3hSmPmlwcTdMx34wgIiLABbyRLU4fq/ m6VKN8L7JCPzFxQLjisZe7CIj0hYofWRWLdKVEScfA8JTd1ZczaH2iXVmy0PtAh+8V mBj4gUBMxH06w== 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 5.15 1/4] locking/semaphore: Use wake_q to wake up processes outside lock critical section Date: Mon, 17 Mar 2025 12:39:46 -0400 Message-Id: <20250317163949.1893632-1-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 5.15.179 Content-Transfer-Encoding: 8bit From: Waiman Long [ Upstream commit 85b2b9c16d053364e2004883140538e73b333cdb ] A circular lock dependency splat has been seen involving down_trylock(): ====================================================== 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.com 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 9ee381e4d2a4d..a26c915430ba0 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); /** * down - acquire the semaphore @@ -182,13 +183,16 @@ EXPORT_SYMBOL(down_timeout); void up(struct semaphore *sem) { unsigned long flags; + DEFINE_WAKE_Q(wake_q); 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); @@ -256,11 +260,12 @@ static noinline int __sched __down_timeout(struct semaphore *sem, long timeout) return __down_common(sem, TASK_UNINTERRUPTIBLE, timeout); } -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 = list_first_entry(&sem->wait_list, struct semaphore_waiter, list); list_del(&waiter->list); waiter->up = true; - wake_up_process(waiter->task); + wake_q_add(wake_q, waiter->task); } -- 2.39.5