From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3493CC28CF6 for ; Wed, 1 Aug 2018 17:59:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C5280208DB for ; Wed, 1 Aug 2018 17:59:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C5280208DB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732360AbeHATqq (ORCPT ); Wed, 1 Aug 2018 15:46:46 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:50156 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405876AbeHATIj (ORCPT ); Wed, 1 Aug 2018 15:08:39 -0400 Received: from localhost (D57E6652.static.ziggozakelijk.nl [213.126.102.82]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id A6C271167; Wed, 1 Aug 2018 17:06:12 +0000 (UTC) From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Kirill Tkhai , Jeff Layton , Sasha Levin Subject: [PATCH 4.17 241/336] fasync: Fix deadlock between task-context and interrupt-context kill_fasync() Date: Wed, 1 Aug 2018 18:49:36 +0200 Message-Id: <20180801165038.282174163@linuxfoundation.org> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20180801165028.930831994@linuxfoundation.org> References: <20180801165028.930831994@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.17-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kirill Tkhai [ Upstream commit 7a107c0f55a3b4c6f84a4323df5610360bde1684 ] I observed the following deadlock between them: [task 1] [task 2] [task 3] kill_fasync() mm_update_next_owner() copy_process() spin_lock_irqsave(&fa->fa_lock) read_lock(&tasklist_lock) write_lock_irq(&tasklist_lock) send_sigio() ... read_lock(&fown->lock) kill_fasync() ... read_lock(&tasklist_lock) spin_lock_irqsave(&fa->fa_lock) ... Task 1 can't acquire read locked tasklist_lock, since there is already task 3 expressed its wish to take the lock exclusive. Task 2 holds the read locked lock, but it can't take the spin lock. Also, there is possible another deadlock (which I haven't observed): [task 1] [task 2] f_getown() kill_fasync() read_lock(&f_own->lock) spin_lock_irqsave(&fa->fa_lock,) send_sigio() write_lock_irq(&f_own->lock) kill_fasync() read_lock(&fown->lock) spin_lock_irqsave(&fa->fa_lock,) Actually, we do not need exclusive fa->fa_lock in kill_fasync_rcu(), as it guarantees fa->fa_file->f_owner integrity only. It may seem, that it used to give a task a small possibility to receive two sequential signals, if there are two parallel kill_fasync() callers, and task handles the first signal fastly, but the behaviour won't become different, since there is exclusive sighand lock in do_send_sig_info(). The patch converts fa_lock into rwlock_t, and this fixes two above deadlocks, as rwlock is allowed to be taken from interrupt handler by qrwlock design. Signed-off-by: Kirill Tkhai Signed-off-by: Jeff Layton Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- fs/fcntl.c | 15 +++++++-------- include/linux/fs.h | 2 +- 2 files changed, 8 insertions(+), 9 deletions(-) --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -871,9 +871,9 @@ int fasync_remove_entry(struct file *fil if (fa->fa_file != filp) continue; - spin_lock_irq(&fa->fa_lock); + write_lock_irq(&fa->fa_lock); fa->fa_file = NULL; - spin_unlock_irq(&fa->fa_lock); + write_unlock_irq(&fa->fa_lock); *fp = fa->fa_next; call_rcu(&fa->fa_rcu, fasync_free_rcu); @@ -918,13 +918,13 @@ struct fasync_struct *fasync_insert_entr if (fa->fa_file != filp) continue; - spin_lock_irq(&fa->fa_lock); + write_lock_irq(&fa->fa_lock); fa->fa_fd = fd; - spin_unlock_irq(&fa->fa_lock); + write_unlock_irq(&fa->fa_lock); goto out; } - spin_lock_init(&new->fa_lock); + rwlock_init(&new->fa_lock); new->magic = FASYNC_MAGIC; new->fa_file = filp; new->fa_fd = fd; @@ -987,14 +987,13 @@ static void kill_fasync_rcu(struct fasyn { while (fa) { struct fown_struct *fown; - unsigned long flags; if (fa->magic != FASYNC_MAGIC) { printk(KERN_ERR "kill_fasync: bad magic number in " "fasync_struct!\n"); return; } - spin_lock_irqsave(&fa->fa_lock, flags); + read_lock(&fa->fa_lock); if (fa->fa_file) { fown = &fa->fa_file->f_owner; /* Don't send SIGURG to processes which have not set a @@ -1003,7 +1002,7 @@ static void kill_fasync_rcu(struct fasyn if (!(sig == SIGURG && fown->signum == 0)) send_sigio(fown, fa->fa_fd, band); } - spin_unlock_irqrestore(&fa->fa_lock, flags); + read_unlock(&fa->fa_lock); fa = rcu_dereference(fa->fa_next); } } --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -1250,7 +1250,7 @@ static inline int locks_lock_file_wait(s } struct fasync_struct { - spinlock_t fa_lock; + rwlock_t fa_lock; int magic; int fa_fd; struct fasync_struct *fa_next; /* singly linked list */