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 4436A35B125 for ; Mon, 30 Mar 2026 09:40:36 +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=1774863636; cv=none; b=ZvDadFOpfkpD+3u4HW1IuPGXFxN+IWLQnKa6q2m/IxjATfqtYmwzlXntKeO97eBHX5/U2c3fUC6t8OwjrXmQmgp+M0wOQlWvcfYse7/Ca84oGG4D6UChh8TGWH/xmMilE4NQveBnjfCygmfDisSB1mUF9alL2GmrQgWB1DpRHbw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774863636; c=relaxed/simple; bh=8YEzImST967gmbnGdp26KkoTKPO1qWKy0g3se6QTWo0=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=lIntYVRx4ULKZBb7P2ObIgeR0ckSEJqVzmI/c7Nu38fPgtiYJRsgh2zeMrZqLl4ou9j+vwsJMzREDIZeMYIzNJ8ARn0tRvdMW+Arf5DHHPEuSXT+zs6PwdHlrAbl1eyIU7KDC9yjpwMEx3APAmne72rDJ7IJgCyjpIG2WgF/HPk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=x0LbQ9Sq; 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="x0LbQ9Sq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B6850C2BCB2; Mon, 30 Mar 2026 09:40:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1774863636; bh=8YEzImST967gmbnGdp26KkoTKPO1qWKy0g3se6QTWo0=; h=Subject:To:Cc:From:Date:From; b=x0LbQ9SqG+NlNLa+9VQCRpnmKa02sN2OZhRClrKlgrYlYra/t+0k0uMxiejTMXkXd llw6ti7e/0+4aeJVmM8g7qjDqaPCT8RpPPT9WpAr5wLS+jcly0r6w7uJexlS4mG69V reGc3p87R8IstGUV2nk2HLk/70n8Nmoiixi/Gw60= Subject: FAILED: patch "[PATCH] futex: Clear stale exiting pointer in futex_lock_pi() retry" failed to apply to 6.6-stable tree To: dave@stgolabs.net,tglx@kernel.org Cc: From: Date: Mon, 30 Mar 2026 11:40:33 +0200 Message-ID: <2026033033-common-quartet-fb0d@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 6.6-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-6.6.y git checkout FETCH_HEAD git cherry-pick -x 210d36d892de5195e6766c45519dfb1e65f3eb83 # git commit -s git send-email --to '' --in-reply-to '2026033033-common-quartet-fb0d@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 210d36d892de5195e6766c45519dfb1e65f3eb83 Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Wed, 25 Mar 2026 17:17:59 -0700 Subject: [PATCH] futex: Clear stale exiting pointer in futex_lock_pi() retry path Fuzzying/stressing futexes triggered: WARNING: kernel/futex/core.c:825 at wait_for_owner_exiting+0x7a/0x80, CPU#11: futex_lock_pi_s/524 When futex_lock_pi_atomic() sees the owner is exiting, it returns -EBUSY and stores a refcounted task pointer in 'exiting'. After wait_for_owner_exiting() consumes that reference, the local pointer is never reset to nil. Upon a retry, if futex_lock_pi_atomic() returns a different error, the bogus pointer is passed to wait_for_owner_exiting(). CPU0 CPU1 CPU2 futex_lock_pi(uaddr) // acquires the PI futex exit() futex_cleanup_begin() futex_state = EXITING; futex_lock_pi(uaddr) futex_lock_pi_atomic() attach_to_pi_owner() // observes EXITING *exiting = owner; // takes ref return -EBUSY wait_for_owner_exiting(-EBUSY, owner) put_task_struct(); // drops ref // exiting still points to owner goto retry; futex_lock_pi_atomic() lock_pi_update_atomic() cmpxchg(uaddr) *uaddr ^= WAITERS // whatever // value changed return -EAGAIN; wait_for_owner_exiting(-EAGAIN, exiting) // stale WARN_ON_ONCE(exiting) Fix this by resetting upon retry, essentially aligning it with requeue_pi. Fixes: 3ef240eaff36 ("futex: Prevent exit livelock") Signed-off-by: Davidlohr Bueso Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260326001759.4129680-1-dave@stgolabs.net diff --git a/kernel/futex/pi.c b/kernel/futex/pi.c index bc1f7e83a37e..7808068fa59e 100644 --- a/kernel/futex/pi.c +++ b/kernel/futex/pi.c @@ -918,7 +918,7 @@ int fixup_pi_owner(u32 __user *uaddr, struct futex_q *q, int locked) int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int trylock) { struct hrtimer_sleeper timeout, *to; - struct task_struct *exiting = NULL; + struct task_struct *exiting; struct rt_mutex_waiter rt_waiter; struct futex_q q = futex_q_init; DEFINE_WAKE_Q(wake_q); @@ -933,6 +933,7 @@ int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int tryl to = futex_setup_timer(time, &timeout, flags, 0); retry: + exiting = NULL; ret = get_futex_key(uaddr, flags, &q.key, FUTEX_WRITE); if (unlikely(ret != 0)) goto out;