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 0E32F3BFE5A; Tue, 16 Jun 2026 18:25:37 +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=1781634338; cv=none; b=RkTcNq6Ab+TnN9s//bgicjytlw0XENirF7XoiaWpn94L2ZCTeVWe5mNWtDLThu+RNO9XJjZd2x0XbTc6urD0rE9M25UQN4oGj+AIykyRUI/UU9XOj1LvEOcAmMiYBdJoadXpLFdDFoTYBuM/s4Cml103G8GybafrorF9qwdNP/E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781634338; c=relaxed/simple; bh=eir/PPOMxwPYXl38KXzhsi6X6Zgi/OGIXVs5pdgPhh8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=KIBF1my/pJyhFYdRkrqoUdmCPKKXbSsT9SpMJOCLEAZaWSWqL5Sdqood29FwP0PoEvnFrVAqEHR3yC97rXPm5ZOPO2H52EOejsXekc/S8qrqlZ7IY/gQ4qrwv9ZyIGvqS/Gl6KJo/dyCPcIwoNuMdRsAXofkEEXgh1TQeXecYSg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=aKIOTTrC; 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="aKIOTTrC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 183D31F000E9; Tue, 16 Jun 2026 18:25:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1781634337; bh=vqPvO0rFebo6RyduTZl9Ba1bGXiirFi6e+bEZyh8y6M=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=aKIOTTrCyXuaSl7wAeelfCHgT+GwwDIDFyHEtEhyaeZPhq90T9eUR7ftUaWhBWMHU wHpwfPMOSgDcUTbC2P//ht/6hg7N+TQGgbQTZTKDTB/p4YtpkBzjJN3Psc6SzQoeeE kYB/iOVFhLKj3yOybQXC2XtQKVpHKwNGAtiN5Wp8= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jeff Layton , Mingyu Wang <25181214217@stu.xidian.edu.cn>, "Christian Brauner (Amutable)" Subject: [PATCH 5.15 246/411] fs/fcntl: fix SOFTIRQ-unsafe lock order in fasync signaling Date: Tue, 16 Jun 2026 20:28:04 +0530 Message-ID: <20260616145114.030355589@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260616145100.376842714@linuxfoundation.org> References: <20260616145100.376842714@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 5.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Mingyu Wang <25181214217@stu.xidian.edu.cn> commit 00633c4683828acd5256fa8d5163f440d74bbe71 upstream. A SOFTIRQ-safe to SOFTIRQ-unsafe lock order deadlock can occur in send_sigio() and send_sigurg() when a process group receives a signal. When FASYNC is configured for a process group (PIDTYPE_PGID), both functions use read_lock(&tasklist_lock) to traverse the task list. However, they are frequently called from softirq context: - send_sigio() via input_inject_event -> kill_fasync - send_sigurg() via tcp_check_urg -> sk_send_sigurg (NET_RX_SOFTIRQ) The deadlock is caused by the rwlock writer fairness mechanism: 1. CPU 0 (process context) holds read_lock(&tasklist_lock) in do_wait(). 2. CPU 1 (process context) attempts write_lock(&tasklist_lock) in fork() or exit() and spins, which blocks all new readers. 3. CPU 0 is interrupted by a softirq (e.g., TCP URG packet reception). 4. The softirq calls send_sigurg() and attempts to acquire read_lock(&tasklist_lock), deadlocking because CPU 1 is waiting. Since PID hashing and do_each_pid_task() traversals are already RCU-protected, the read_lock on tasklist_lock is no longer strictly required for safe traversal. Fix this by replacing tasklist_lock with rcu_read_lock(), aligning the process group signaling path with the single-PID path. This also mitigates a potential remote denial of service vector via TCP URG packets. Lockdep splat: ===================================================== WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected [...] Chain exists of: &dev->event_lock --> &f_owner->lock --> tasklist_lock Possible interrupt unsafe locking scenario: CPU0 CPU1 ---- ---- lock(tasklist_lock); local_irq_disable(); lock(&dev->event_lock); lock(&f_owner->lock); lock(&dev->event_lock); *** DEADLOCK *** Reviewed-by: Jeff Layton Signed-off-by: Mingyu Wang <25181214217@stu.xidian.edu.cn> Link: https://patch.msgid.link/20260523135210.590928-1-w15303746062@163.com Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Greg Kroah-Hartman --- fs/fcntl.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -801,11 +801,11 @@ void send_sigio(struct fown_struct *fown send_sigio_to_task(p, fown, fd, band, type); rcu_read_unlock(); } else { - read_lock(&tasklist_lock); + rcu_read_lock(); do_each_pid_task(pid, type, p) { send_sigio_to_task(p, fown, fd, band, type); } while_each_pid_task(pid, type, p); - read_unlock(&tasklist_lock); + rcu_read_unlock(); } out_unlock_fown: read_unlock_irqrestore(&fown->lock, flags); @@ -842,11 +842,11 @@ int send_sigurg(struct fown_struct *fown send_sigurg_to_task(p, fown, type); rcu_read_unlock(); } else { - read_lock(&tasklist_lock); + rcu_read_lock(); do_each_pid_task(pid, type, p) { send_sigurg_to_task(p, fown, type); } while_each_pid_task(pid, type, p); - read_unlock(&tasklist_lock); + rcu_read_unlock(); } out_unlock_fown: read_unlock_irqrestore(&fown->lock, flags);