From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f177.google.com ([209.85.192.177]:36291 "EHLO mail-pf0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751802AbcFIC77 (ORCPT ); Wed, 8 Jun 2016 22:59:59 -0400 Received: by mail-pf0-f177.google.com with SMTP id t190so8577288pfb.3 for ; Wed, 08 Jun 2016 19:59:59 -0700 (PDT) From: Tahsin Erdogan To: Tejun Heo , Alexander Viro Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Tahsin Erdogan Subject: [PATCH] writeback: inode cgroup wb switch should skip inode with zero i_count Date: Wed, 8 Jun 2016 19:59:28 -0700 Message-Id: <1465441168-17738-1-git-send-email-tahsin@google.com> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Asynchronous wb switching of inodes takes an additional ref count on an inode to make sure inode remains valid until switchover is completed. However, it is possible that inode->i_count has already reached zero while inode is in writeback queue: ------------[ cut here ]------------ WARNING: CPU: 1 PID: 917 at fs/inode.c:397 ihold+0x2b/0x30 CPU: 1 PID: 917 Comm: kworker/u4:5 Not tainted 4.7.0-rc2+ #49 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 Workqueue: writeback wb_workfn (flush-8:16) 0000000000000000 ffff88007ca0fb58 ffffffff805990af 0000000000000000 0000000000000000 ffff88007ca0fb98 ffffffff80268702 0000018d000004e2 ffff88007cef40e8 ffff88007c9b89a8 ffff880079e3a740 0000000000000003 Call Trace: [] dump_stack+0x4d/0x6e [] __warn+0xc2/0xe0 [] warn_slowpath_null+0x18/0x20 [] ihold+0x2b/0x30 [] inode_switch_wbs+0x11c/0x180 [] wbc_detach_inode+0x170/0x1a0 [] writeback_sb_inodes+0x21c/0x530 [] wb_writeback+0xee/0x1e0 [] wb_workfn+0xd7/0x280 [] ? try_to_wake_up+0x1b1/0x2b0 [] process_one_work+0x129/0x300 [] worker_thread+0x126/0x480 [] ? __schedule+0x1c7/0x561 [] ? process_one_work+0x300/0x300 [] kthread+0xc4/0xe0 [] ? kfree+0xc8/0x100 [] ret_from_fork+0x1f/0x40 [] ? __kthread_parkme+0x70/0x70 ---[ end trace aaefd2fd9f306bc4 ]--- Signed-off-by: Tahsin Erdogan --- fs/fs-writeback.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 989a2ce..b44ede0 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -478,14 +478,15 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id) spin_lock(&inode->i_lock); if (!(inode->i_sb->s_flags & MS_ACTIVE) || inode->i_state & (I_WB_SWITCH | I_FREEING) || + atomic_read(&inode->i_count) == 0 || inode_to_wb(inode) == isw->new_wb) { spin_unlock(&inode->i_lock); goto out_free; } inode->i_state |= I_WB_SWITCH; + ihold(inode); spin_unlock(&inode->i_lock); - ihold(inode); isw->inode = inode; atomic_inc(&isw_nr_in_flight); -- 2.8.0.rc3.226.g39d4020