[Bug 44731] ext4 deadlock under heavy io?

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https://bugzilla.kernel.org/show_bug.cgi?id=44731





--- Comment #2 from Anssi Hannula <anssi.hannula@iki.fi>  2012-07-16 20:54:14 ---
Created an attachment (id=75501)
 --> (https://bugzilla.kernel.org/attachment.cgi?id=75501)
sysrq-w output on 3.4.2 with frozen filesystem dm-4

I'm seeing a very similar issue on 3.4.2. I think this issue didn't exist
several major versions back.

When one or more applications do intensive I/O, the filesystem freezes and all
processes trying to access it freeze as well.

It doesn't always happen in the same way, though. Sometimes I get the "task
blocked for more than 120 seconds", but sometimes I don't (in the attached case
I didn't get those). Also, sometimes the system becomes usable again after
several minutes of being seemingly frozen, but often it doesn't recover (like
in the attached case). If wanted, I can provide more logs of these different
situations (the logs do look very similar than the ones on this report,
though).

In the attachment the frozen fs is dm-4. It is on the same LVM VG and RAID-6 as
dm-3, dm-5, dm-6, and those other filesystems continued to work while dm-4 was
frozen.

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