Re: [Qemu-devel] [Qemu-stable] Recent patches for 2.4

[Peter Lieven <pl@kamp.de>]

Am 07.09.2015 um 18:28 schrieb Paolo Bonzini:
>
> On 03/09/2015 15:11, Peter Lieven wrote:
>>>>>> edec47c main-loop: fix qemu_notify_event for aio_notify optimization
>>>>> Part of the above AioContext series.
>>>> So either the whole series or none of them I guess?
>>> It's a separate bug, and theoretically it's there in 2.3.1 as well, but
>>> no one ever reproduced it (it would hang in make check) so not
>>> worthwhile.
>> I maybe found another case where this bugfix seems to help. For various
>> reasons I'm still on 2.2.1 stable with some CVE fixes manually applied.
> Don't be ashamed to say that! :)
>
>> I currently work on the problem that a haning NFS Server where I mount
>> my CDROM ISOs from takes down the whole vServer because the main loop
>> hangs sooner or later.
>>
>> I already put some patches on the list which help to improve the situation:
>>
>> ide/atapi: make PIO read requests async
>> block/io: allow AIOCB without callback
>> ide/atapi: partially avoid deadlock if the storage backend is dead
>> block/nfs: cache allocated filesize for read-only files
>>
>> However, I ended up with one case where Qemu deadlocks in bdrv_drain_one.
>>
>> Scenario:
>>  - Windows 2012R2 with a random ISO mounted.
>>  - Block communication to NFS via Firewall
>>  - execute 'eject ide1-cd0' in the HMP
>>  - restore connectivity.
>>
>> The HMP hangs forever even if the NFS connectivity itself is restored.
> If that patch helps, it's not a problem to include it in other stable
> releases.

It helps, but I have a small issue when my backport of the patch
is applied.

I launch qemu witch a cmdline like this to probe for enforcable CPU types.

echo quit | qemu -enable-kvm -monitor stdio -nodefaults -nographic -cpu Haswell,enforce -S

Qemu hangs when entering the quit command. If I omit the -S it works. And without the
fix it also works with -S.

My backport (Linux only and without tests etc.) of the original fix is here:
https://github.com/plieven/qemu/commit/0ddcdc62a85f705017df16421d769e82b70f9b37

Maybe I made a mistake.

Peter