From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 A959D4028F2 for ; Mon, 15 Jun 2026 15:20:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781536826; cv=none; b=Z5ND6wnJnlXeC8xCz/6Kjl+yHhbABNtLgOIh2oQPp6Ky64o4izlgzbEiMDb0IZ9Q+y+fXtKTw775Kj2T/lPPYY8KOZyEvz0x104/1eD/csGzCERzG+10nCFNb1bpHfs4ua3xR76EEqT6ur/RctN9au3qYZCcn+ec8qNyYZZi2ig= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781536826; c=relaxed/simple; bh=uXUx+/h0UnVyyQ4JovuaKox04AEEl7iSABa+rb+qPv4=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=IrzA8CeNQscBllC6Stytg/gMdrW9ZomlitUapNqk4dVw8Olm/AW9mG7XAKdjUUpFhk+oXJf/W+G4v2CgWKHJRzcjSPlIKXGckkThMifnoqjn5IQdFhPx9hySVCMPaI0iHowsdjGBXgr19L0ZRWzI/e/9fpeMIl1oHXqjDD6qhc4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=OTE0KYHq; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="OTE0KYHq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C359C1F000E9; Mon, 15 Jun 2026 15:20:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1781536825; bh=Wf09Ui4Xn/ebkgTMvVM0cHzE6JHZzUwjaKEn/OIy++M=; h=Subject:To:Cc:From:Date; b=OTE0KYHqEi85QRN0i27jR4UEeybLaQWYa9QPHMuDleDfpo22ga90hcVjoG/lxzh3e //lq2nwudkTes+D/OhcKPkOEoDTzzIoRg++iZSRIpJXWzZVSKy70qHs1yQoDvICE6Q GIhkcynn5a+d7ir5VLH0+slaa8UIk+scLZpJpmfU= Subject: FAILED: patch "[PATCH] locking/rtmutex: Skip remove_waiter() when waiter is not" failed to apply to 6.1-stable tree To: dave@stgolabs.net,tglx@kernel.org Cc: From: Date: Mon, 15 Jun 2026 16:47:18 +0200 Message-ID: <2026061518-quilt-plaything-413e@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.1-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y git checkout FETCH_HEAD git cherry-pick -x 40a25d59e85b3c8709ac2424d44f65610467871e # git commit -s git send-email --to '' --in-reply-to '2026061518-quilt-plaything-413e@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 40a25d59e85b3c8709ac2424d44f65610467871e Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Thu, 7 May 2026 04:29:13 -0700 Subject: [PATCH] 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 instead 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 early 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 remove_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 diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c index 4f386ea6c792..daeeeef973e2 100644 --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1558,6 +1558,9 @@ static void __sched remove_waiter(struct rt_mutex_base *lock, lockdep_assert_held(&lock->wait_lock); + if (!waiter_task) /* never enqueued */ + return; + scoped_guard(raw_spinlock, &waiter_task->pi_lock) { rt_mutex_dequeue(lock, waiter); waiter_task->pi_blocked_on = NULL; diff --git a/kernel/locking/rtmutex_api.c b/kernel/locking/rtmutex_api.c index 124219aea46e..514fce7a4e0a 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_base *lock, raw_spin_lock_irq(&lock->wait_lock); ret = __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);