From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f52.google.com (mail-pa0-f52.google.com [209.85.220.52]) by kanga.kvack.org (Postfix) with ESMTP id C6E7E6B0037 for ; Fri, 20 Sep 2013 08:52:34 -0400 (EDT) Received: by mail-pa0-f52.google.com with SMTP id kq13so670179pab.11 for ; Fri, 20 Sep 2013 05:52:34 -0700 (PDT) Subject: [PATCH] writeback: fix delayed sync(2) From: Maxim Patlasov Date: Fri, 20 Sep 2013 16:52:26 +0400 Message-ID: <20130920125029.17356.66782.stgit@dhcp-10-30-17-2.sw.ru> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org Cc: tj@kernel.org, akpm@linux-foundation.org, fengguang.wu@intel.com, jack@suse.cz, linux-kernel@vger.kernel.org Problem statement: if sync(2) races with bdi_wakeup_thread_delayed (which is called when the first inode for a bdi is marked dirty), it's possible that sync will be delayed for long (5 secs if dirty_writeback_interval is set to default value). How it works: sync schedules bdi work for immediate processing by calling mod_delayed_work with 'delay' equal to 0. Bdi work is queued to pool->worklist and wake_up_worker(pool) is called, but before worker gets the work from the list, __mark_inode_dirty intervenes calling bdi_wakeup_thread_delayed who calls mod_delayed_work with 'timeout' equal to dirty_writeback_interval multiplied by 10. mod_delayed_work dives into try_to_grab_pending who successfully steals the work from the worklist. Then it's re-queued with that new delay. Until the timeout is lapsed, sync(2) sits on wait_for_completion in sync_inodes_sb. The patch uses queue_delayed_work for __mark_inode_dirty. This should be safe because even if queue_delayed_work returns false (if the work is already on a queue), bdi_writeback_workfn will re-schedule itself by looking at wb->b_dirty. Signed-off-by: Maxim Patlasov --- mm/backing-dev.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/backing-dev.c b/mm/backing-dev.c index ce682f7..3fde024 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -294,7 +294,7 @@ void bdi_wakeup_thread_delayed(struct backing_dev_info *bdi) unsigned long timeout; timeout = msecs_to_jiffies(dirty_writeback_interval * 10); - mod_delayed_work(bdi_wq, &bdi->wb.dwork, timeout); + queue_delayed_work(bdi_wq, &bdi->wb.dwork, timeout); } /* -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org