Re: Commit 7eaceaccab5f40 causing boot hang.

[Richard Kennedy <richard@rsk.demon.co.uk>]

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