Re: [Qemu-devel] [Qemu-block] [PATCH v2 0/3] block: pause block jobs for bdrv_drain_begin/end

[Paolo Bonzini]

On 23/03/2017 18:44, Stefan Hajnoczi wrote:
>> It's possible to wedge QEMU if the guest tries to reset a virtio-pci
>> device as QEMU is also using the drive for a blockjob. This patchset
>> aims to allow us to safely pause/resume jobs attached to individual
>> nodes in a manner similar to how bdrv_drain_all_begin/end do.
> 
> Weird, I thought the 0 nanosecond sleep that block jobs do in their
> main loop allows aio_poll() loops to finish.

The 0 nanosecond sleep is now done in the BDS AioContext rather than in 
the "non-aio_poll-aware" main loop:

    commit 0b9caf9b3166c8deb3c4f3a774c2384b069dc29c
    Author: Fam Zheng <address@hidden>
    Date:   Tue Aug 26 15:15:43 2014 +0800

    coroutine: Drop co_sleep_ns
    
    block_job_sleep_ns is the only user. Since we are moving towards
    AioContext aware code, it's better to use the explicit version and drop
    the old one.
    
    Signed-off-by: Fam Zheng <address@hidden>
    Reviewed-by: Benoît Canet <address@hidden>
    Signed-off-by: Stefan Hajnoczi <address@hidden>

> I've CCed Fam because I think he has also tackled this issue in the past.

Yes, he fixed the same issue for bdrv_drain_all.

Paolo