From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754126AbcI1JbO (ORCPT ); Wed, 28 Sep 2016 05:31:14 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:57389 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932298AbcI1JIM (ORCPT ); Wed, 28 Sep 2016 05:08:12 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Brian Foster , Christoph Hellwig , Dave Chinner Subject: [PATCH 4.4 46/73] xfs: prevent dropping ioend completions during buftarg wait Date: Wed, 28 Sep 2016 11:05:16 +0200 Message-Id: <20160928090437.686691977@linuxfoundation.org> X-Mailer: git-send-email 2.10.0 In-Reply-To: <20160928090434.509091655@linuxfoundation.org> References: <20160928090434.509091655@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Brian Foster commit 800b2694f890cc35a1bda63501fc71c94389d517 upstream. xfs_wait_buftarg() waits for all pending I/O, drains the ioend completion workqueue and walks the LRU until all buffers in the cache have been released. This is traditionally an unmount operation` but the mechanism is also reused during filesystem freeze. xfs_wait_buftarg() invokes drain_workqueue() as part of the quiesce, which is intended more for a shutdown sequence in that it indicates to the queue that new operations are not expected once the drain has begun. New work jobs after this point result in a WARN_ON_ONCE() and are otherwise dropped. With filesystem freeze, however, read operations are allowed and can proceed during or after the workqueue drain. If such a read occurs during the drain sequence, the workqueue infrastructure complains about the queued ioend completion work item and drops it on the floor. As a result, the buffer remains on the LRU and the freeze never completes. Despite the fact that the overall buffer cache cleanup is not necessary during freeze, fix up this operation such that it is safe to invoke during non-unmount quiesce operations. Replace the drain_workqueue() call with flush_workqueue(), which runs a similar serialization on pending workqueue jobs without causing new jobs to be dropped. This is safe for unmount as unmount independently locks out new operations by the time xfs_wait_buftarg() is invoked. cc: Signed-off-by: Brian Foster Reviewed-by: Christoph Hellwig Signed-off-by: Dave Chinner Signed-off-by: Greg Kroah-Hartman --- fs/xfs/xfs_buf.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/fs/xfs/xfs_buf.c +++ b/fs/xfs/xfs_buf.c @@ -1535,7 +1535,7 @@ xfs_wait_buftarg( * ensure here that all reference counts have been dropped before we * start walking the LRU list. */ - drain_workqueue(btp->bt_mount->m_buf_workqueue); + flush_workqueue(btp->bt_mount->m_buf_workqueue); /* loop until there is nothing left on the lru list. */ while (list_lru_count(&btp->bt_lru)) {