linux-kernel - Re: BUG at mm/filemap.c:1749 (2.6.24, jffs2, unionfs)

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Message-Id: <200710191738.l9JHccYx011061@agora.fsl.cs.sunysb.edu>
Date:	Fri, 19 Oct 2007 13:38:38 -0400
From:	Erez Zadok <ezk@...sunysb.edu>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Erez Zadok <ezk@...sunysb.edu>, dwmw2@...radead.org,
	jffs-dev@...s.com, linux-kernel@...r.kernel.org,
	linux-mtd@...ts.infradead.org
Subject: Re: BUG at mm/filemap.c:1749 (2.6.24, jffs2, unionfs) 

In message <200710191716.53470.nickpiggin@...oo.com.au>, Nick Piggin writes:
[...]
> Hmm, looks like jffs2_write_end is writing more than we actually ask it
> to, and returns that back.
> 
>         unsigned aligned_start = start & ~3;
> 
> and
> 
>         if (end == PAGE_CACHE_SIZE) {
>                 /* When writing out the end of a page, write out the
>                    _whole_ page. This helps to reduce the number of
>                    nodes in files which have many short writes, like
>                    syslog files. */
>                 start = aligned_start = 0;
>         }
> 
> These "longer" writes are fine, but they shouldn't get propagated back
> to the vm/vfs. Something like the following patch might fix it.
> 
> 
> --Boundary-00=_lnFGHwOggSRGKPd
> Content-Type: text/x-diff;
>   charset="utf-8";
>   name="jffs2-writtenlen-fix.patch"
> Content-Transfer-Encoding: 7bit
> Content-Disposition: attachment;
> 	filename="jffs2-writtenlen-fix.patch"

Nick, the patch worked.  All of my unionfs-over-jffs2 tests passed.

Thanks,
Erez.
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