linux-kernel - Re: Regression in suspend to ram in 2.6.31-rc kernels

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Message-ID: <87ljkvmt71.fsf@devron.myhome.or.jp>
Date:	Fri, 04 Sep 2009 09:47:46 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Zdenek Kabelac <zdenek.kabelac@...il.com>
Cc:	Christoph Hellwig <hch@....de>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mmc@...r.kernel.org, viro@...iv.linux.org.uk
Subject: Re: Regression in suspend to ram in 2.6.31-rc kernels

Christoph Hellwig <hch@....de> writes:

> On Fri, Sep 04, 2009 at 12:29:04AM +0200, Zdenek Kabelac wrote:
>> Ok - another bisect game played - and unexpected winner is:
>> 
>> (fat: add ->sync_fs)
>> 
>> f83d6d46e7adf241a064a4a425e5cd8a8fd8925f
>> 
>> Reverting this commit with current -rc8 kernel makes the system happy
>> during the suspend/resume cycle. Obviously it has it price :) so just
>> plain revert is probably not a good solution so the problem looks
>> 'more serious'  (fat is not the only fs with this patch) thus adding
>> original author to this thread.

>From it, I suspect the possible reason seems to read mmc after remove
event. I.e. the following sequence or something

    sync fs process
    [...]
    removed mmc event
    [...]
    fat_sync_fs()                   <- sync again?
        fat_clusters_flush()
            sb_bread()              <- read block on removed mmc

Can you add dump_stack() to the top of fat_sync_fs()? I hope it tells
why fat_sync_fs() is called (it is called from device unplug event?).

Well, that commit seems a bit strange. It calls fat_clusters_flush()
unconditionally without checking sb->s_dirt. However, if my guess is
right, "sync after removed event" itself sounds like the issue in
suspend process.

Thanks.

> Note that when you rever this patch on a current kernel you do actually
> get different behvaviour than when going back to before this commit.
>
> In 2.6.30 we called ->write_super in the various sync functions and
> then ->sync_fs, in 2.6.31-rc8 you would not call any syncing at all
> anymore.  I think this patch might just be a symptom for a situation
> where the suspend code causes a sync and the mmc driver can't handle
> it anymore.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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