From nobody Mon Jun 8 09:49:26 2026 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 AFC333A3816; Wed, 3 Jun 2026 20:16:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780517775; cv=none; b=fw6k2boULuFJGY29+8TbkNuankE70FCBpSeEns01P4Su+ubHjJY5IOrNxiQTQ4lExkAVFnJBFpcUtb41GKU/nNsPhh3Pk5vdyNDQtd+dd52pMO5Ru667MrrtMdQ3oM1tk/Xps9AhWpj5w58cdyhdCwj80p/wknNRW2uNQTNOqf0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780517775; c=relaxed/simple; bh=ljWLbcWqPQqUQqC+Y9aEHfuzUNNwSOwpXPzUrs/XVno=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=sgFPzN31wjUPBSlpgzhcGX5oZMsJISrme0xLuykN+zCw7hyRR9hv/a4uxXm+fYV0/p0efVVtlPJ/jZ3HeEn/tOH+YVwPemqgs4JCzcd0tAoCl70WsljCR8I5qtVl3rEDdSYSrYu6jJtIilh3apwK74kGUoSjqM3GS2j/aKPiOKg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=WMWwsoze; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=I+PuS+yi; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="WMWwsoze"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="I+PuS+yi" Date: Wed, 03 Jun 2026 20:16:08 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1780517772; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=HaAcml/hsg87+10WXExvmobFW3lWSh2IJIWZcKaC2PQ=; b=WMWwsozel6zE39ywRYVesQBSYcrqYp1wUyF04v0SUthnmgMXjWlpTf0K3PckrdJZwYOJjE p44vcYZ0l4go1n3ku7Cjg8Fr0CwxMCL6nA5VNVhhRSJxRyT968E6Oa9NglEfPBbgcrCq6j U8hxrmTUrAV5xB2lpOSU5Gk6UvZWT9j4OKAycpdYhft5SC32MeaCEg4FinKxT+yGPSqBje eeE5M29GNwT9M9wYUezUx1wkfC5Iklc9pcyE/Viw1+CeqM76QiqPiwkuVPltKHvXW6tZcg cileJwmaQ8qg02i42wdlD+rtXKRakaFB1B0YE8U3P/VmwtrAX+eHQk0WYeOUag== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1780517772; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=HaAcml/hsg87+10WXExvmobFW3lWSh2IJIWZcKaC2PQ=; b=I+PuS+yiYv8/fHgSwAmj3Jov+A27CiRDLiiv5lGSoOgpPo5Nds+XxQdL4jQj90DMKPDukR XMlzNOVciHl770BA== From: "tip-bot2 for Davidlohr Bueso" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: locking/urgent] locking/rtmutex: Skip remove_waiter() when waiter is not enqueued Cc: syzbot+78147abe6c524f183ee9@syzkaller.appspotmail.com, Davidlohr Bueso , Thomas Gleixner , stable@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20260507112913.1019537-1-dave@stgolabs.net> References: <20260507112913.1019537-1-dave@stgolabs.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <178051776811.710.17500090454720140903.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the locking/urgent branch of tip: Commit-ID: 40a25d59e85b3c8709ac2424d44f65610467871e Gitweb: https://git.kernel.org/tip/40a25d59e85b3c8709ac2424d44f65610= 467871e Author: Davidlohr Bueso AuthorDate: Thu, 07 May 2026 04:29:13 -07:00 Committer: Thomas Gleixner CommitterDate: Wed, 03 Jun 2026 22:11:53 +02:00 locking/rtmutex: Skip remove_waiter() when waiter is not enqueued syzbot triggered the following splat in remove_waiter() via FUTEX_CMP_REQUEUE_PI: KASAN: null-ptr-deref in range [0x0000000000000a88-0x0000000000000a8f] class_raw_spinlock_constructor remove_waiter+0x159/0x1200 kernel/locking/rtmutex.c:1561 rt_mutex_start_proxy_lock+0x103/0x120 futex_requeue+0x10e4/0x20d0 __x64_sys_futex+0x34f/0x4d0 task_blocks_on_rt_mutex() does not arm the waiter upon deadlock detection, leaving waiter->task nil, where 3bfdc63936dd ("rtmutex: Use waiter::task in= stead of current in remove_waiter()") made this fatal. Furthermore, rt_mutex_start_proxy_lock() should not be calling into remove_= waiter() upon a successfully grabbing the rtmutex. 1a1fb985f2e2 ("futex: Handle earl= y deadlock return correctly"), moved the remove_waiter() out of __rt_mutex_start_proxy= _lock() (where 'ret' was only ever 0 or < 0) into the wrapper. Tighten this check to account for try_to_take_rt_mutex(). Fixes: 3bfdc63936dd ("rtmutex: Use waiter::task instead of current in remov= e_waiter()") Reported-by: syzbot+78147abe6c524f183ee9@syzkaller.appspotmail.com Signed-off-by: Davidlohr Bueso Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Closes: https://lore.kernel.org/all/69f114ac.050a0220.ac8b.0003.GAE@google.= com/ Link: https://patch.msgid.link/20260507112913.1019537-1-dave@stgolabs.net --- kernel/locking/rtmutex.c | 3 +++ kernel/locking/rtmutex_api.c | 2 +- 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 4f386ea..daeeeef 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1558,6 +1558,9 @@ static void __sched remove_waiter(struct rt_mutex_bas= e *lock, =20 lockdep_assert_held(&lock->wait_lock); =20 + if (!waiter_task) /* never enqueued */ + return; + scoped_guard(raw_spinlock, &waiter_task->pi_lock) { rt_mutex_dequeue(lock, waiter); waiter_task->pi_blocked_on =3D NULL; diff --git a/kernel/locking/rtmutex_api.c b/kernel/locking/rtmutex_api.c index 124219a..514fce7 100644 --- a/kernel/locking/rtmutex_api.c +++ b/kernel/locking/rtmutex_api.c @@ -365,7 +365,7 @@ int __sched rt_mutex_start_proxy_lock(struct rt_mutex_b= ase *lock, =20 raw_spin_lock_irq(&lock->wait_lock); ret =3D __rt_mutex_start_proxy_lock(lock, waiter, task, &wake_q); - if (unlikely(ret)) + if (unlikely(ret < 0)) remove_waiter(lock, waiter); preempt_disable(); raw_spin_unlock_irq(&lock->wait_lock);