linux-ext4 - Re: WARNING at fs/ext4/inode.c ext4_evict

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Date:	Fri, 17 Jun 2016 20:04:34 +0200
From:	Jan Kara <jack@...e.cz>
To:	Calvin Owens <calvinowens@...com>
Cc:	Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org,
	kernel-team@...com
Subject: Re: WARNING at fs/ext4/inode.c ext4_evict_inode() triggers on 4.0

On Fri 17-06-16 13:40:33, Calvin Owens wrote:
> On Thursday 06/16 at 10:33 +0200, Jan Kara wrote:
> > Hi Calvin,
> > 
> > On Wed 15-06-16 16:49:39, Calvin Owens wrote:
> > > I'm hitting the following warning on a 4.0 kernel:
> > > 
> > >   WARNING: CPU: 15 PID: 1005611 at fs/ext4/inode.c:233 ext4_evict_inode+0x4be/0x4d0()
> > >   CPU: 15 PID: 1005611 Comm: rocksdb:bg0 Not tainted 4.0.9-60_fbk10_rc1_3974_g796b9b6 #1
> > >   Call Trace: 
> > >   [<ffffffff8176af8e>] dump_stack+0x4d/0x63
> > >   [<ffffffff8106c4dc>] warn_slowpath_common+0x8c/0xd0
> > >   [<ffffffff8106c5da>] warn_slowpath_null+0x1a/0x20
> > >   [<ffffffff81242c0e>] ext4_evict_inode+0x4be/0x4d0
> > >   [<ffffffff811d248b>] evict+0xbb/0x190 
> > >   [<ffffffff811d2d6d>] iput+0x17d/0x1e0
> > >   [<ffffffff811ce0e0>] __dentry_kill+0x190/0x1e0
> > >   [<ffffffff811ce2d1>] dput+0x1a1/0x1f0
> > >   [<ffffffff811b952a>] __fput+0x17a/0x210
> > >   [<ffffffff811b960e>] ____fput+0xe/0x10
> > >   [<ffffffff81086dbf>] task_work_run+0xbf/0x100 
> > >   [<ffffffff81002bcc>] do_notify_resume+0x7c/0x90
> > >   [<ffffffff81771529>] int_signal+0x12/0x17
> > > 
> > > Commit 822dbba ("ext4: fix warning in ext4_evict_inode()") proportedly fixed
> > > this in 3.11. The check was entirely removed in 4.6.
> > 
> > OK, so this is the warning:
> > 
> > WARN_ON(atomic_read(&EXT4_I(inode)->i_ioend_count));
> > 
> > It was removed in 4.6 since we maintained i_ioend_count only to be able to
> > do this check and it didn't trigger for a long time. So it is interesting
> > that it actually triggered for you with 4.0.
> > 
> > > Is it interesting to you that this triggers on 4.0? I can revert 600be30 and
> > > see if I can reproduce it on upstream, but since the check got removed I
> > > was wondering if there was post-4.0 work that makes it obsolete?
> > 
> > It would be great. I'm attaching a revert and an additional debug patch. If
> > you can run with these two on the latest kernel (or even just apply the debug
> > patch on top of 4.0) and reproduce the issue with it, I would be grateful.
> 
> Forgot to attach the patches? Or did my mailserver eat them? :)

Sorry, probably forgot to attach. Here they are.

									Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

View attachment "0001-Revert-ext4-remove-i_ioend_count.patch" of type "text/x-patch" (2980 bytes)

View attachment "0002-ext4-Debug-outstanding-io_ends.patch" of type "text/x-patch" (4659 bytes)