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[Qemu-devel] [BUG] VM abort after migration

From: longpeng
Subject: [Qemu-devel] [BUG] VM abort after migration
Date: Wed, 3 Jul 2019 08:34:16 +0000

Hi guys,

We found a qemu core in our testing environment, the assertion
'assert(bus->irq_count[i] == 0)' in pcibus_reset() was triggered and
the bus->irq_count[i] is '-1'.

Through analysis, it was happened after VM migration and we think
it was caused by the following sequence:

*Migration Source*
1. save bus pci.0 state, including irq_count[x] ( =0 , old )
2. save E1000:
      pci_set_irq --> update pci_dev->irq_state to 1 and
                  update bus->irq_count[x] to 1 ( new )
    the irq_state sent to dest.

*Migration Dest*
1. Receive the irq_count[x] of pci.0 is 0 , but the irq_state of e1000 is 1.
2. If the e1000 need change irqline , it would call to pci_irq_handler(),
  the irq_state maybe change to 0 and bus->irq_count[x] will become
  -1 in this situation.
3. do VM reboot then the assertion will be triggered.

We also found some guys faced the similar problem:
[1] https://lists.gnu.org/archive/html/qemu-devel/2016-11/msg02525.html
[2] https://bugs.launchpad.net/qemu/+bug/1702621

Is there some patches to fix this problem ?
Can we save pcibus state after all the pci devs are saved ?


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