linux-kernel - Re: [PATCH] [MTD] Fix JFFS2 sync silent failure

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Message-ID: <20100419101559.GA4145@logfs.org>
Date:	Mon, 19 Apr 2010 12:15:59 +0200
From:	Jörn Engel <joern@...fs.org>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH] [MTD] Fix JFFS2 sync silent failure

On Mon, 19 April 2010 09:38:44 +0200, Jens Axboe wrote:
> On Sat, Apr 17 2010, Jörn Engel wrote:
> > Moin David,
> > 
> > if I read the code correctly, JFFS2 will happily perform a NOP on
> > sys_sync() again.  And this time it appears to be Jens' fault.
> > 
> > JFFS2 does not appear to set s_bdi anywhere.  And as of 32a88aa1,
> > __sync_filesystem() will return 0 if s_bdi is not set.  As a result,
> > sync_fs() is never called for jffs2 and whatever remains in the wbuf
> > will not make it to the device.
> > 
> > The patch also adds a BUG_ON to catch this problem in any remaining or
> > future offenders.  I am not sure about network filesystems, but at
> > least bdev- and mtd-based ones should be caught.
> > 
> > Opinions?
> 
> I think that BUG_ON() would be a lot better as a printk() and fail mount
> instead. There's really little point in killing the kernel for something
> you could easily warn about and recover nicely.

*shrug*
The BUG_ON directly above is not qualitatively different.  In both cases
the only solution is to find and fix the bug in some other file,
recompile and try again.  But ultimately I don't care, as long as we
catch the bug before people lose their data.

Feel free to respin this patch.  You caused the problem in the first
place. ;)

For the record, while I consider the two-liner that causes this mess a
real turd, the rest of your patch was brilliant.  A shame I didn't catch
this earlier.

Jörn

-- 
You ain't got no problem, Jules. I'm on the motherfucker. Go back in
there, chill them niggers out and wait for the Wolf, who should be
coming directly.
-- Marsellus Wallace
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