linux-ext4 - Re: [PATCH] ext4: drop file_update_time from ext4_dax

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Message-ID: <20151123141556.GK23418@quack.suse.cz>
Date:	Mon, 23 Nov 2015 15:15:56 +0100
From:	Jan Kara <jack@...e.cz>
To:	Dave Chinner <david@...morbit.com>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	Ted Ts'o <tytso@....edu>, linux-nvdimm@...ts.01.org,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Jan Kara <jack@...e.com>
Subject: Re: [PATCH] ext4: drop file_update_time from ext4_dax_fault

On Fri 20-11-15 14:03:44, Dave Chinner wrote:
> On Thu, Nov 19, 2015 at 04:18:13PM -0800, Dan Williams wrote:
> >  WARNING: CPU: 0 PID: 2133 at fs/fs-writeback.c:2065 __mark_inode_dirty+0x261/0x350()
> >  bdi-block not registered
>    ^^^^^^^^^^^^^^^^^^^^^^^^
> >  [..]
> >  Call Trace:
> >   [<ffffffff81459f62>] dump_stack+0x44/0x62
> >   [<ffffffff810a2052>] warn_slowpath_common+0x82/0xc0
> >   [<ffffffff810a20ec>] warn_slowpath_fmt+0x5c/0x80
> >   [<ffffffff812831a1>] __mark_inode_dirty+0x261/0x350
> >   [<ffffffff8126d109>] generic_update_time+0x79/0xd0
> >   [<ffffffff8126d28d>] file_update_time+0xbd/0x110
> >   [<ffffffff812e4bc8>] ext4_dax_fault+0x68/0x110
> >   [<ffffffff811f816e>] __do_fault+0x4e/0xf0
> >   [<ffffffff811fc2a7>] handle_mm_fault+0x5e7/0x1b50
> >   [<ffffffff811fbd11>] ? handle_mm_fault+0x51/0x1b50
> >   [<ffffffff810689c1>] __do_page_fault+0x191/0x3f0
> >   [<ffffffff81068cef>] trace_do_page_fault+0x4f/0x120
> >   [<ffffffff8106314a>] do_async_page_fault+0x1a/0xa0
> >   [<ffffffff81902678>] async_page_fault+0x28/0x30
> 
> Doesn't this indicate some problem at the block/bdi level?
> __mark_inode_dirty() should not throw warnings like this regardless
> of where it is called from...

The warning warns that we are dirtying inodes against a backing device that
advertises it does writeback but is not registered with writeback code (so
flusher does not run for it). That makes sense but people seem to be
experimenting a lot with removing devices under filesystems lately and so
this warning triggers. Probably we have to refine it to not trigger for
such cases...

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