Re: [Qemu-devel] [PATCH 01/18] iothread: release iothread around aio_poll

[Stefan Hajnoczi]

On Thu, Aug 06, 2015 at 03:35:59PM +0200, Paolo Bonzini wrote:
> This is the first step towards having fine-grained critical sections in
> dataplane threads, which resolves lock ordering problems between
> address_space_* functions (which need the BQL when doing MMIO, even
> after we complete RCU-based dispatch) and the AioContext.
> 
> Because AioContext does not use contention callbacks anymore, the
> unit test has to be changed.
> 
> Previously applied as a0710f7995f914e3044e5899bd8ff6c43c62f916 and
> then reverted.

commit da5e1de95bb235330d7724316e7a29239d1359d5
Author: Stefan Hajnoczi <address@hidden>
Date:   Wed Jun 3 10:15:33 2015 +0100

    Revert "iothread: release iothread around aio_poll"
    
    This reverts commit a0710f7995f914e3044e5899bd8ff6c43c62f916.
    
    In qemu-devel email message <address@hidden>, Christian
    Borntraeger writes:
    
      Having many guests all with a kernel/ramdisk (via -kernel) and
      several null block devices will result in hangs. All hanging
      guests are in partition detection code waiting for an I/O to return
      so very early maybe even the first I/O.
    
      Reverting that commit "fixes" the hangs.
    
    Reverting this commit for the 2.4 release.  More time is needed to
    investigate and correct this patch.

Did we ever find the root cause for hangs caused by this patch?