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SubjectRe: 2.4.18-14 kernel stuck during ext3 umount with ping still responding
Date
Hi,

The problem reproduces on a 2.4.18-19 kernel as well. Took some more time
but finally it roared its ugly head.

This is the stack trace from the new kernel:

>c01190b8 f3791eb4 set_running_and_schedule
>c010a8b0 f3791ed0 enable_irq
>c014200c f3791f0c IO_APIC_get_PCI_irq_vector
>c0155595 f3791f0c clear_inode
>c01556639 f3791f60 invalidate_inodes
>c0149629 f3791f8 set_binfmt
>c0157c58 f3791f94 sys_umount
>c0108cab 0f3791fc0 sys_sigaltstack


Andrew Morton suggested a buffer.c patch for reducing search complexity,
which I will try next.

Any further comments/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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