[linux-lvm] DM suspend locks up under load?

[David Shaw]

On Jan 5, 2012, at 5:44 AM, Zdenek Kabelac wrote:

> Dne 4.1.2012 23:50, David Shaw napsal(a):
>> Hi,
>> 
>> 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-2.6.35.6-45.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
-stable.git;a=commitdiff;h=be4f27d324e8ddd57cc0d4d604fe85ee0425cba9

David