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Date: Fri, 2 Aug 2013 12:01:02 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [RFC v2 3/5] timer: make qemu_clock_enable sync
 between disable and timer's cb
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To: liu ping fan <qemulist@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, Alex Bligh <alex@alex.org.uk>, Jan Kiszka <jan.kiszka@siemens.com>, qemu-devel@nongnu.org, Anthony Liguori <anthony@codemonkey.ws>

 On Aug 02 2013, liu ping fan wrote:
> On Thu, Aug 1, 2013 at 10:28 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> > > > > > So actually there is another problem with this patch (both the
> > > > > > condvar and the event approach are equally buggy).  If a timer
> > > > > > on clock X disables clock X, qemu_clock_enable will deadlock.
> >
> > Checking the code for callers of qemu_clock_enable() it seems like there
> > shouldn't be any deadlocks.  So it should work if qemu_clock_enable
> 
> Do you mean the caller of qemu_clock_enable(foo,false) can NOT be
> timer cb?

Yes.

> As for this deadlock issue, making
> qemu_clock_enable(foo,false) ASYNC, and forcing the caller to sync
> explicitly ?

Right now the callers of qemu_clock_enable(foo, false) are safe.  So
the problem can be "fixed" just by adequate documentation.

> > But we should document the expectations since they are different from
> > the current code.
> >
> > Paolo