Re: [Qemu-devel] [PATCH] cpus: make qemu_mutex_iothread_locked() understand co-routines

[Stefan Hajnoczi]

On Tue, Nov 01, 2016 at 04:21:36PM +0000, Alex Bennée wrote:
> 
> Paolo Bonzini <address@hidden> writes:
> 
> > On 21/10/2016 13:54, Alex Bennée wrote:
> >> There is a slight wart when checking for the state of the BQL when using
> >> GThread base co-routines (which we keep for ThreadSanitizer runs). While
> >> the main-loop holds the BQL it is suspended until the co-routine
> >> completes however the co-routines run in a separate thread so checking
> >> the TLS variable could be wrong.
> >>
> >> We fix this by expanding the check to include qemu_in_coroutine() for
> >> GThread based builds. As it is not used for production builds I'm not
> >> overly worried about any performance impact which should be negligible
> >> anyway.
> >>
> >> Signed-off-by: Alex Bennée <address@hidden>
> >> Cc: Stefan Hajnoczi <address@hidden>
> >
> > This is wrong unfortunately.  It is possible to run coroutines outside
> > the BQL (e.g. with -device virtio-blk,iothread=foo).
> >
> > Do you know exactly why TSAN has no love for coroutines?
> 
> The current production stuff is due to missing support for new stacks
> with setcontext. However I have built the latest tsan support library
> and that seems happy without the gthread co-routines.
> 
> Currently I'm dealing with glib's racy gthread support however.

I think Paolo suggested we drop the GThread backend on IRC.  I agree
that we should do that since GThread co-routines break code that uses
thread-local variables and have never truly worked.

Stefan

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