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SubjectRe: 2.6.34 echo j > /proc/sysrq-trigger causes inifnite unfreeze/Thaw event
Dave Chinner wrote:
> On Thu, Jun 03, 2010 at 11:30:30PM -0600, Jeffrey Merkey wrote:
>> causes the FS Thaw stuff in fs/buffer.c to enter an infinite loop
>> filling the /var/log/messages with junk and causing the hard drive to
>> crank away endlessly.
>
> Hmmm, looks pretty obvious what the 2.6.34 bug is:
>
> while (sb->s_bdev && !thaw_bdev(sb->s_bdev, sb))
> printk(KERN_WARNING "Emergency Thaw on %s\n",
> bdevname(sb->s_bdev, b));
>
> thaw_bdev() returns 0 on success or not frozen, and returns non-zero
> only if the unfreeze failed. Looks like it was broken from the start
> to me.

thaw_bdev() used to return -EINVAL for not-frozen, but it no longer
does. Seems commit 4504230a dropped this:

- if (!bdev->bd_fsfreeze_count) {
- mutex_unlock(&bdev->bd_fsfreeze_mutex);
- return -EINVAL;
- }
in favor of this:

+ int error = -EINVAL;
...
+ if (!bdev->bd_fsfreeze_count)
+ goto out_unlock;
...
+out_unlock:
mutex_unlock(&bdev->bd_fsfreeze_mutex);
return 0;
and now we return 0 for a thaw of a non-frozen bdev ....
this breaks the loop in the emergency thaw-er (which was
just supposed to work its way through nested freezes,
when I wrote it)
-Eric


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