[linux-lvm] DM suspend locks up under load?
dshaw at jabberwocky.com
Tue Jan 10 23:20:20 UTC 2012
On Jan 5, 2012, at 5:44 AM, Zdenek Kabelac wrote:
> Dne 4.1.2012 23:50, David Shaw napsal(a):
>> I'm using some code that creates a snapshot using DM directly (we aren't using LVM), using essentially:
>> suspend linear device X
>> reload X as a "snapshot-origin" device
>> create "snapshot" device
>> resume original X device (which is now a snapshot-origin)
>> This has worked fine for several years. Recently, however, we updated to a more recent system, and ext4, and are seeing something odd. Under load, the process above freezes at the first suspend step, and locks up the device in question, requiring a reboot to fix things.
>> I wrote the attached program to demonstrate the problem. All it does it call DM_DEVICE_SUSPEND and DM_DEVICE_RESUME over and over on a DM device. Basically, run the test program on any mounted linear DM target in one shell, then delete a lot of data from a directory residing on that device in another shell. On my systems this will freeze both the test program and the rm in D state, and require a reboot to fix things.
>> I've tried multiple different kernels, but at the moment, I'm using kernel-PAE-126.96.36.199-45.fc14.i686 and device-mapper-libs-1.02.63-2.fc14.i686.
>> One clue I can add is that it only seems to happen if the filesystem on the device is ext4. It does not happen with ext3.
>> Any ideas on where I should look next?
> Maybe you should suspect ext4 - if there is no problem with dm & ext3 ?
> I guess you need to get stacktrace where the system locks.
> (echo t >/proc/sysrq-trigger - or Sysrq+T)
> You should probably also try different kernel.
Thanks for the tip! It did indeed turn out to be ext4, and it was already fixed: http://git.kernel.org/?p=linux/kernel/git/stable/linux
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