linux-kernel - Re: [BUG]2.6.27.y some contents lost after writing to mmaped file

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Date:	Wed, 18 Nov 2009 22:17:56 +0800
From:	JiSheng Zhang <jszhang3@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Chris Mason <chris.mason@...cle.com>, Greg KH <gregkh@...e.de>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	stable@...nel.org, jack@...e.cz, rmk@....linux.org.uk,
	linux-arm@...ts.infradead.org
Subject: Re: [BUG]2.6.27.y some contents lost after writing to mmaped file

On Tue, 17 Nov 2009 20:06:35 +0100
Jan Kara <jack@...e.cz> wrote:

> On Tue 17-11-09 07:36:22, Chris Mason wrote:
> > On Mon, Nov 16, 2009 at 05:56:55PM -0800, Greg KH wrote:
> > > On Mon, Nov 16, 2009 at 11:38:57AM +0800, JiSheng Zhang wrote:
> > > > Hi,
> > > > 
> > > > I triggered a failure in an fs test with fsx-linux from ltp. It seems that
> > > > fsx-linux failed at mmap->write sequence.
> > > > 
> > > > Tested kernel is 2.6.27.12 and 2.6.27.39
> > > 
> > > Does this work on any kernel you have tested?  Or is it a regression?
> > > 
> > > > Tested file system: ext3, tmpfs.
> > > > IMHO, it impacts all file systems.
> > > > 
> > > > Some fsx-linux log is:
> > > > 
> > > > READ BAD DATA: offset = 0x2771b, size = 0xa28e
> > > > OFFSET  GOOD    BAD     RANGE
> > > > 0x287e0 0x35c9  0x15a9     0x80
> > > > operation# (mod 256) for the bad datamay be 21
> > > > ...
> > > > 7828: 1257514978.306753 READ     0x23dba thru 0x25699 (0x18e0 bytes)
> > > > 7829: 1257514978.306899 MAPWRITE 0x27eeb thru 0x2a516 (0x262c bytes)
> > > >  ******WWWW
> > > > 7830: 1257514978.307504 READ     0x2771b thru 0x319a8 (0xa28e bytes)
> > > >  ***RRRR***
> > > > Correct content saved for comparison
> > > > ...
>   Hmm, how long does it take to reproduce? I'm running fsx-linux on tmpfs
> for a while on 2.6.27.21 and didn't hit the problem yet.

I forget to mention that the test were done on an arm board with 64M ram. 
I have tested fsx-linux again on pc, it seems that failure go away.

> 
> > > Are you sure that the LTP is correct?  It wouldn't be the first time it
> > > wasn't...
> > 
> > I'm afraid fsx usually finds bugs.  I thought Jan Kara recently fixed
> > something here in ext3, does 2.6.32-rc work?
>   Yeah, fsx usually finds bugs. Note that he sees the problem also on tmpfs
> so it's not ext3 problem. Anyway, trying to reproduce with 2.6.32-rc? would
> be interesting.

Currently the arm board doesn't support 2.6.32-rc. But I test with 2.6.32-rc7
On my pc box, there's no failure so far.

> 
> 								Honza

I found this via google:
http://marc.info/?t=118026315000001&r=1&w=2

I even tried the code from
http://marc.info/?l=linux-arch&m=118030601701617&w=2
I got mostly:
firstfirstfirst
firstfirstfirst
firstfirstfirst


No change after pass "MS_SYNC|MS_INVALIDATE" to msync and make the 
flush_dcache_page() call unconditional in do_generic_mapping_read.
This behavior is different from what I read from the mail thread above.

> void do_generic_mapping_read(struct address_space *mapping,
>                              struct file_ra_state *_ra,
>                              struct file *filp,
>                              loff_t *ppos,
>                              read_descriptor_t *desc,
>                              read_actor_t actor)
> {
> ...
>                 /* If users can be writing to this page using arbitrary
>                  * virtual addresses, take care about potential aliasing
>                  * before reading the page on the kernel side.
>                  */
>                 if (1 || mapping_writably_mapped(mapping))
>                         flush_dcache_page(page);

Then I run fsx-linux after the above modification, fsx-linux failed all 
the same both on tmpfs and ext3
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