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

[Paolo Bonzini <pbonzini@redhat.com>]

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.

Paolo