[Bug 1645636] Re: deadlock during lvm snapshot

[Guillaume Penin]

Hi all,

I think we just hit the same bug on a Production server today, with a
snapshot on the root filesystem. Here are the relevant logs :

kernel: [455151.056975] INFO: task jbd2/dm-0-8:214 blocked for more than 120 seconds.
kernel: [455151.149417] INFO: task dmeventd:27193 blocked for more than 120 seconds.
kernel: [455151.241272] INFO: task cat:27522 blocked for more than 120 seconds.
...

All I/Os on the filesystem were blocked, so we had to reboot the server.

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https://bugs.launchpad.net/bugs/1645636

Title:
  deadlock during lvm snapshot

Status in lvm2 package in Ubuntu:
  Confirmed

Bug description:
  I'm doing backup of a running mongodb using LVM snapshot. Sometimes I
  run into a deadlock situation and kernel reports blocked tasks for jbd2,
  mongod, dmeventd and my tar doing backup.

  This happens very rarely (one in a thousand) but the effect is rather
  severe as mongodb stops working. I also can't remove and unmount the
  snapshot.

  I have Ubuntu 16.04.1 (lvm2 2.02.133-1ubuntu10) with mongod 3.2.9 on a
  64bit system.

  According to the link below its a kernel race with considerably
  decreased chance in latest lvm2 package.

  https://www.redhat.com/archives/linux-lvm/2016-November/msg00037.html

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