Re: [Qemu-devel] [PATCH] block: Fix race in gluster_finish_aiocb

[Asias He]

On Wed, Aug 21, 2013 at 10:16:02AM +0200, Paolo Bonzini wrote:
> Il 21/08/2013 04:02, Asias He ha scritto:
> > In block/gluster.c, we have
> > 
> > gluster_finish_aiocb
> > {
> >    if (retval != sizeof(acb)) {
> >       qemu_mutex_lock_iothread(); /* We are in gluster thread context */
> >       ...
> >       qemu_mutex_unlock_iothread();
> >    }
> > }
> > 
> > qemu tools, e.g. qemu-img, might race here because
> > qemu_mutex_{lock,unlock}_iothread are a nop operation and
> > gluster_finish_aiocb is in the gluster thread context.
> > 
> > To fix, we introduce our own mutex for qemu tools.
> > 
> > Signed-off-by: Asias He <address@hidden>
> > ---
> >  stubs/iothread-lock.c | 11 +++++++++++
> >  1 file changed, 11 insertions(+)
> > 
> > diff --git a/stubs/iothread-lock.c b/stubs/iothread-lock.c
> > index 5d8aca1..d5c6dec 100644
> > --- a/stubs/iothread-lock.c
> > +++ b/stubs/iothread-lock.c
> > @@ -1,10 +1,21 @@
> >  #include "qemu-common.h"
> >  #include "qemu/main-loop.h"
> >  
> > +static QemuMutex qemu_tools_mutex;
> > +static pthread_once_t qemu_tools_once = PTHREAD_ONCE_INIT;
> 
> Doesn't work on Windows, but you can just add

Hmm, Any reasons, why it does not work on Windows?

> __attribute__((__constructor__)) to qemu_tools_mutex_init.

__attribute__((__constructor__)) works on Windows?

> Paolo
> 
> > +static void qemu_tools_mutex_init(void)
> > +{
> > +    qemu_mutex_init(&qemu_tools_mutex);
> > +}
> > +
> >  void qemu_mutex_lock_iothread(void)
> >  {
> > +    pthread_once(&qemu_tools_once, qemu_tools_mutex_init);
> > +    qemu_mutex_lock(&qemu_tools_mutex);
> >  }
> >  
> >  void qemu_mutex_unlock_iothread(void)
> >  {
> > +    qemu_mutex_unlock(&qemu_tools_mutex);
> >  }
> > 
> 

-- 
Asias