Message-ID: <4DA57CC0.8010400@fusionio.com>
Date:	Wed, 13 Apr 2011 12:36:48 +0200
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Richard Kennedy <richard@....demon.co.uk>
CC:	Tejun Heo <tj@...nel.org>, Rob Landley <rlandley@...allels.com>,
	Pete Clements <clem@...m.clem-digital.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>
Subject: Re: Commit 7eaceaccab5f40 causing boot hang.

On 2011-04-13 12:25, Richard Kennedy wrote:
> On Mon, 2011-04-04 at 14:47 +0100, Richard Kennedy wrote:
>> On Thu, 2011-03-31 at 15:49 +0100, Richard Kennedy wrote:
>>> On Thu, 2011-03-31 at 15:33 +0200, Jens Axboe wrote:
>>> [...]
>>>>>>> Hi Jens,
>>>>>>>
>>>>>>> I'm seeing a problem with fio never completing when writing to 2 disks
>>>>>>> simultaneously. In my test case I'm writing 2Gb to both a LVM volume & a
>>>>>>> pata drive on x86_64 on a AMD X2. Could this be a related issue?
>>>>>>>
>>>>>>> I'm not getting anything reported in the log, lockup detection doesn't
>>>>>>> report anything either. The write seems to have finished (the disk light
>>>>>>> activity has stopped) and the cpu cores are both below 10% usage, but
>>>>>>> fio never returns. The test does complete some times, but it seems to be
>>>>>>> one 1 in 4.
>>>>>>
>>>>>> So when you say PATA, it's /dev/hdaX something as well?
>>>>>>
>>>>>>> I'm going to try tracing it and see if I can spot where it's stuck.
>>>>>>
>>>>>> Thanks, that would be nice.
>>>>>>
>>>>> The second drive is /dev/sdb1 mounted on /opt, both file systems are
>>>>> ext4.
>>>>
>>>> So probably not related. What does the fio job look like?
>>>>
>>> fio job file --
>>> [global]
>>> pre_read=1
>>> ioengine=mmap
>>>
>>> [f1]
>>> size=2g
>>> rw=write
>>> directory=/home/tests
>>>
>>> [f2]
>>> size=2g
>>> rw=write
>>> directory=/opt/tests
>>>
>>> Fio gets run from a script that also collects stats but it's been
>>> running without any problems up until 2.6.39-rc1.
>>>
>> Hi Jens
>> I've upgrade to the latest fio version in the git repo 1.51 and I'm
>> still seeing this problem. 
>>
>> Fio gets stuck after it writes the 100% complete message and strace on
>> the processes shows this.
>>
>> the controlling fio process :- 
>>  ...
>> [pid  8439] wait4(8442, 0x7fff848203ac, WNOHANG, NULL) = 0
>> [pid  8439] nanosleep({0, 10000000}, NULL) = 0
>> [pid  8439] wait4(8441, 0x7fff848203ac, WNOHANG, NULL) = 0
>> [pid  8439] wait4(8442, 0x7fff848203ac, WNOHANG, NULL) = 0
>> [pid  8439] nanosleep({0, 10000000}
>>
>> & the 2 workers are both stopped here, strace shows only the one line
>> for each process.
>>
>> Process 8441 attached - interrupt to quit
>> futex(0x7f9db76a802c, FUTEX_WAIT_PRIVATE, 2, NULL
>>
>>
>> Process 8442 attached - interrupt to quit
>> futex(0x7f9db76a802c, FUTEX_WAIT_PRIVATE, 2, NULL
>>
>> How do I find out which futex it's waiting for? 
>> Any ideas where I should look next ?
>>
>> I can run the same test successfully on 2.6.38 so is it worth trying to
>> bisect this ? 
>>
>> thanks 
>> Richard
>>
> My problem has gone away in v2.6.39-rc3.
> I've just finished bisecting it down to 6de9843dab3f, & that got
> reverted in rc3, so no problem ;)
> 
> (The data corruption caused by that faulty commit was zeroing out the
> shared mutexs in fio & the worker threads were getting stuck on the
> writeout_mutex.)

Great, that's one less regression to worry about :-)


-- 
Jens Axboe

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