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SubjectRe: 2.4.18-14 kernel stuck during ext3 umount with ping still responding
Date
Well, took some time to reproduce the environment with the kernel including 
the patch, but seems it didn't help after all.

The ctrl-scroll-lock output shows a stuck umount in R status, with a similar
call trace as before, but the inner calls a little different:

c0141295 __wait_on_buffer
c014200c fsync_buffers_list
c0155595 f25f9efc clear_inode
c015553d f25f9f2c invalidate_inodes
c01461d8 f25f9f78 get_super
c014a629 f25f9f94 path_release
c0157c58 f25f9fc0 sys_umount
c0108cab sys_sigaltstack

This is using a 2.4.18-19.7 kernel patched as per the below suggestion.

Any pointers/suggestions are welcome

Thanks,
Yuval








>From: Andrew Morton <akpm@digeo.com>
>To: yuval yeret <yuval_yeret@hotmail.com>
>CC: linux-kernel@vger.kernel.org, yuval@exanet.com
>Subject: Re: 2.4.18-14 kernel stuck during ext3 umount with ping still
>responding
>Date: Thu, 09 Jan 2003 02:06:55 -0800
>
>yuval yeret wrote:
> >
> > Hi,
> >
> > I'm running a 2.4.18-14 kernel with a heavy IO profile using ext3 over
>RAID
> > 0+1 volumes.
> >
> > >From time to time I get a black screen stuck machine while trying to
>umount
> > a volume during an IO workload (as part of a failback solution - but
>after
> > killing all IO processes ), with ping still responding, but everything
>else
> > mostly dead.
> >
> > I tried using the forcedumount patch to solve this problem - to no
>avail.
> > Also tried upgrading the qlogic drivers to the latest drivers from
>Qlogic.
> >
> > After one of the occurences I managed to get some output using the sysrq
> > keys.
> >
> > This seems similar to what is described in
> > http://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=77508 but with a
> > different call trace
> >
> > What I have here is what I managed to copy down (for some reason
>pgup/pgdown
> > didn't work so not all information is full...) together with a manual
>lookup
> > of the call trace
> > from /proc/ksyms :
> >
> > process umount
> > EIP c01190b8 (set_running_and_schedule)
> > call trace:
> > c01144c9 f25f9ec0 IO_APIC_get_PCI_irq_vector
> > c010a8b0 f25f9ed0 enable_irq
> > c014200c f25f9ef0 fsync_buffers_list
> > c0155595 f25f9efc clear_inode
> > c015553d f25f9f2c invalidate_inodes
> > c01461d8 f25f9f78 get_super
> > c014a629 f25f9f94 path_release
> > c0157c58 f25f9fc0 sys_umount
> > c0108cab sys_sigaltstack
> >
> > Any idea what can cause this ?
> >
>
>If you have a large amount of data against two or more filesystems,
>and you try to unmount one of them the kernel can seize up for a
>very long time in the fsync_dev()->sync_buffers() function. Under
>these circumstances that function has O(n*n) search complexity
>and n is quite large.
>
>However your backtrace shows neither of those functions.
>
>Still, as an experiment it would be interesting to see if the below
>patch fixes it up. It converts O(n*n) to O(m), where m > n.
>
>
>
> fs/buffer.c | 6 +++---
> 1 files changed, 3 insertions(+), 3 deletions(-)
>
>--- 2420/fs/buffer.c~a Thu Jan 9 02:03:06 2003
>+++ 2420-akpm/fs/buffer.c Thu Jan 9 02:04:02 2003
>@@ -307,11 +307,11 @@ int sync_buffers(kdev_t dev, int wait)
> * 2) write out all dirty, unlocked buffers;
> * 2) wait for completion by waiting for all buffers to unlock.
> */
>- write_unlocked_buffers(dev);
>+ write_unlocked_buffers(NODEV);
> if (wait) {
>- err = wait_for_locked_buffers(dev, BUF_DIRTY, 0);
>+ err = wait_for_locked_buffers(NODEV, BUF_DIRTY, 0);
> write_unlocked_buffers(dev);
>- err |= wait_for_locked_buffers(dev, BUF_LOCKED, 1);
>+ err |= wait_for_locked_buffers(NODEV, BUF_LOCKED, 1);
> }
> return err;
> }
>
>_


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