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 C7E1030C61D; Mon, 13 Oct 2025 15:36:39 +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=1760369799; cv=none; b=M5VaUX/dr3OqOBBmvDhh/IflQ7ro9OmAApTzGf/hnILcrI+ISJ3DjYNGYn9fDw9V4HzqzqVUJqL76QJGwdboOvjIN8C0r/6uot8ESac0TS8xNxu7gOGaOitJ0pdAsaObyWGzKlBVZEZ/BRmTxNj0WCfSMWO+GL3dZCdheTLmhaI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760369799; c=relaxed/simple; bh=eedAXoRqqXz/z0suBO7t4xhvz85YjpXtbrSd86Qu3Qk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ISQtpg7+ci3wT+k/8pu387urfByiwr5g0k4kCN0v122PWLy2IcK7IAFLfz3DmkIOQuK9Id1qWxFaqYTT6NY2qJkfrnLNr3NBMbZsjzLWLAJZfkJWeVlTlNCpPnyR1IuDDaRJfUpS28g4iFJYKN9jUYeBL93sI8nRhtUcriBkaiw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=byxr73UG; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="byxr73UG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 01ACDC4CEE7; Mon, 13 Oct 2025 15:36:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1760369799; bh=eedAXoRqqXz/z0suBO7t4xhvz85YjpXtbrSd86Qu3Qk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=byxr73UG+PTD/GV85Lgo3HeVQ9OeHU1o0n80szwwZSDADwhEz46VUZkY49sDw1F8c 5bFqyFlGbWyMY/1EtI7N7jSxGIlRImfQJgUo0v0V2KSmZbT0hrhko3kG1T+lRl8hzd VlcK7M7ZncebUqkGU8vz1UgV8nfANv00RWdwR+84= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+10b4363fb0f46527f3f3@syzkaller.appspotmail.com, Sebastian Andrzej Siewior , Takashi Iwai , Sasha Levin Subject: [PATCH 6.17 371/563] ALSA: pcm: Disable bottom softirqs as part of spin_lock_irq() on PREEMPT_RT Date: Mon, 13 Oct 2025 16:43:52 +0200 Message-ID: <20251013144424.715569077@linuxfoundation.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251013144411.274874080@linuxfoundation.org> References: <20251013144411.274874080@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.17-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sebastian Andrzej Siewior [ Upstream commit 9fc4a3da9a0259a0500848b5d8657918efde176b ] snd_pcm_group_lock_irq() acquires a spinlock_t and disables interrupts via spin_lock_irq(). This also implicitly disables the handling of softirqs such as TIMER_SOFTIRQ. On PREEMPT_RT softirqs are preemptible and spin_lock_irq() does not disable them. That means a timer can be invoked during spin_lock_irq() on the same CPU. Due to synchronisations reasons local_bh_disable() has a per-CPU lock named softirq_ctrl.lock which synchronizes individual softirq against each other. syz-bot managed to trigger a lockdep report where softirq_ctrl.lock is acquired in hrtimer_cancel() in addition to hrtimer_run_softirq(). This is a possible deadlock. The softirq_ctrl.lock can not be made part of spin_lock_irq() as this would lead to too much synchronisation against individual threads on the system. To avoid the possible deadlock, softirqs must be manually disabled before the lock is acquired. Disable softirqs before the lock is acquired on PREEMPT_RT. Reported-by: syzbot+10b4363fb0f46527f3f3@syzkaller.appspotmail.com Fixes: d2d6422f8bd1 ("x86: Allow to enable PREEMPT_RT.") Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Takashi Iwai Signed-off-by: Sasha Levin --- sound/core/pcm_native.c | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-) diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c index 1eab940fa2e5a..68bee40c9adaf 100644 --- a/sound/core/pcm_native.c +++ b/sound/core/pcm_native.c @@ -84,19 +84,24 @@ void snd_pcm_group_init(struct snd_pcm_group *group) } /* define group lock helpers */ -#define DEFINE_PCM_GROUP_LOCK(action, mutex_action) \ +#define DEFINE_PCM_GROUP_LOCK(action, bh_lock, bh_unlock, mutex_action) \ static void snd_pcm_group_ ## action(struct snd_pcm_group *group, bool nonatomic) \ { \ - if (nonatomic) \ + if (nonatomic) { \ mutex_ ## mutex_action(&group->mutex); \ - else \ - spin_ ## action(&group->lock); \ -} - -DEFINE_PCM_GROUP_LOCK(lock, lock); -DEFINE_PCM_GROUP_LOCK(unlock, unlock); -DEFINE_PCM_GROUP_LOCK(lock_irq, lock); -DEFINE_PCM_GROUP_LOCK(unlock_irq, unlock); + } else { \ + if (IS_ENABLED(CONFIG_PREEMPT_RT) && bh_lock) \ + local_bh_disable(); \ + spin_ ## action(&group->lock); \ + if (IS_ENABLED(CONFIG_PREEMPT_RT) && bh_unlock) \ + local_bh_enable(); \ + } \ +} + +DEFINE_PCM_GROUP_LOCK(lock, false, false, lock); +DEFINE_PCM_GROUP_LOCK(unlock, false, false, unlock); +DEFINE_PCM_GROUP_LOCK(lock_irq, true, false, lock); +DEFINE_PCM_GROUP_LOCK(unlock_irq, false, true, unlock); /** * snd_pcm_stream_lock - Lock the PCM stream -- 2.51.0