Re: [Qemu-devel] [PATCH v2] vl: pause vcpus before stopping iothreads

[Stefan Hajnoczi]

On Thu, Feb 01, 2018 at 11:07:08AM +0000, Stefan Hajnoczi wrote:
> Commit dce8921b2baaf95974af8176406881872067adfa ("iothread: Stop threads
> before main() quits") introduced iothread_stop_all() to avoid the
> following virtio-scsi assertion failure:
> 
>   assert(blk_get_aio_context(d->conf.blk) == s->ctx);
> 
> Back then the assertion failed because when bdrv_close_all() made
> d->conf.blk NULL, blk_get_aio_context() returned the global AioContext
> instead of s->ctx.
> 
> The same assertion can still fail today when vcpus submit new I/O
> requests after iothread_stop_all() has moved the BDS to the global
> AioContext.
> 
> This patch hardens the iothread_stop_all() approach by pausing vcpus
> before calling iothread_stop_all().
> 
> Note that the assertion failure is a race condition.  It is not possible
> to reproduce it reliably.
> 
> Signed-off-by: Stefan Hajnoczi <address@hidden>
> ---
> v2:
>  * Add comment explaining rationale for this ordering and why it's safe.
>    [Kevin]
> 
>  vl.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan

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