From: Calvin Owens <calvinowens@fb.com>
Subject: Re: WARNING at fs/ext4/inode.c ext4_evict_inode() triggers on 4.0
Date: Fri, 17 Jun 2016 13:40:33 -0400
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 <20160616083304.GD22835@quack2.suse.cz>
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To: Jan Kara <jack@suse.cz>
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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? :)

Thanks,
Calvin

> Also if you reproduce the issue, please send me also your System.map so that
> I can map the address of the function where ioend was created. Thanks!
> 
> 									Honza
> -- 
> Jan Kara <jack@suse.com>
> SUSE Labs, CR