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