Re: [Qemu-devel] [Bug 1570134] Re: While committing snapshot qemu crashes with SIGABRT

[Max Reitz <mreitz@redhat.com>]

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On 20.04.2016 20:09, Max Reitz wrote:
> On 20.04.2016 02:03, Matthew Schumacher wrote:
>> Max,
>>
>> Qemu still crashes for me, but the debug is again very different.  When
>> I attach to the qemu process from gdb, it is unable to provide a
>> backtrace when it crashes.  The log file is different too.  Any ideas?
>>
>> qemu-system-x86_64: block.c:2307: bdrv_replace_in_backing_chain:
>> Assertion `!bdrv_requests_pending(old)' failed.
> 
> This message is exactly the same as you saw in 2.5.1, so I guess we've
> at least averted a regression in 2.6.0.

I get the same message in 2.5.0, in 2.4.0 it's "Co-routine re-entered
recursively". 2.3.0 works fine.

Bisecting the regression between 2.3.0 and 2.4.0 interestingly yields
48ac0a4df84662f as the problematic commit, but I can't imagine that this
is the root issue. The effective change it brings is that for active
commits, the buf_size is no longer the same as the granularity, but the
default mirror buf_size instead.

When forcing buf_size to the granularity, the issue first appears with
commit 3f09bfbc7bee812 (after 2.4.0, before 2.5.0), which is much less
surprising, because this is the one that introduced the assertion in the
first place.

However, I still don't think the assertion is the problem but the fact
that the guest device can still send requests after bdrv_drained_begin().

Max


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