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

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Date:	Fri, 20 Nov 2009 11:41:02 +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, rmk@....linux.org.uk,
	linux-arm@...ts.infradead.org
Subject: Re: [BUG]2.6.27.y some contents lost after writing to mmaped file

Hi,

Russell King wrote
>- CPU type
ARM926EJ-S
>- is it a SMP CPU
no. UP
>- are you running a SMP kernel
no
>- board type
an soc


>- the storage peripheral being used for this test
memory and harddrive
>- is DMA being used for this periperal
for memory, DMA? for harddrive, yes
>- any additional block layers (eg, lvm, dm, md)
no
>- filesystem type
tmpfs and ext3

2009/11/18 JiSheng Zhang <jszhang3@...il.com>:
> 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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