Re: [Qemu-devel] [PATCH] trace: add qemu mutex lock and unlock trace events

[joserz]

On Mon, Apr 24, 2017 at 10:45:52PM +0800, Fam Zheng wrote:
> On Mon, 04/24 11:28, Jose Ricardo Ziviani wrote:
> > These trace events were very useful to help me to understand and find a
> > reordering issue in vfio, for example:
> > 
> > qemu_mutex_lock locked mutex 0x10905ad8
> >   vfio_region_write  (0001:03:00.0:region1+0xc0, 0x2020c, 4)
> > qemu_mutex_unlock unlocked mutex 0x10905ad8
> > qemu_mutex_lock locked mutex 0x10905ad8
> >   vfio_region_write  (0001:03:00.0:region1+0xc4, 0xa0000, 4)
> > qemu_mutex_unlock unlocked mutex 0x10905ad8
> > 
> > that also helped to see desired result after the fix:
> > 
> > qemu_mutex_lock locked mutex 0x10905ad8
> >   vfio_region_write  (0001:03:00.0:region1+0xc0, 0x2000c, 4)
> >   vfio_region_write  (0001:03:00.0:region1+0xc4, 0xb0000, 4)
> > qemu_mutex_unlock unlocked mutex 0x10905ad8
> > 
> > So it could be a good idea to have these traces implemented. It's worth
> > mentioning that they should be surgically enabled during the debugging,
> > otherwise it'd flood the trace logs with lock/unlock messages.
> > 
> > How to use it:
> > trace-event qemu_mutex_lock on|off
> > trace-event qemu_mutex_unlock on|off
> > or
> > trace-event qemu_mutex* on|off
> > 
> > Signed-off-by: Jose Ricardo Ziviani <address@hidden>
> > ---
> >  util/qemu-thread-posix.c | 5 +++++
> >  util/trace-events        | 4 ++++
> >  2 files changed, 9 insertions(+)
> > 
> > diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
> > index 73e3a0e..909c2ac 100644
> > --- a/util/qemu-thread-posix.c
> > +++ b/util/qemu-thread-posix.c
> > @@ -14,6 +14,7 @@
> >  #include "qemu/thread.h"
> >  #include "qemu/atomic.h"
> >  #include "qemu/notify.h"
> > +#include "trace.h"
> >  
> >  static bool name_threads;
> >  
> > @@ -60,6 +61,8 @@ void qemu_mutex_lock(QemuMutex *mutex)
> >      err = pthread_mutex_lock(&mutex->lock);
> >      if (err)
> >          error_exit(err, __func__);
> > +
> > +    trace_qemu_mutex_lock((void *)&mutex->lock);
> 
> You don't need these casts as the parameter type is void * which accepts any
> pointers.

OK

> 
> >  }
> >  
> >  int qemu_mutex_trylock(QemuMutex *mutex)
> > @@ -74,6 +77,8 @@ void qemu_mutex_unlock(QemuMutex *mutex)
> >      err = pthread_mutex_unlock(&mutex->lock);
> >      if (err)
> >          error_exit(err, __func__);
> > +
> > +    trace_qemu_mutex_unlock((void *)&mutex->lock);
> >  }
> >  
> >  void qemu_rec_mutex_init(QemuRecMutex *mutex)
> > diff --git a/util/trace-events b/util/trace-events
> > index b44ef4f..65c33fe 100644
> > --- a/util/trace-events
> > +++ b/util/trace-events
> > @@ -55,3 +55,7 @@ lockcnt_futex_wait_prepare(const void *lockcnt, int 
> > expected, int new) "lockcnt
> >  lockcnt_futex_wait(const void *lockcnt, int val) "lockcnt %p waiting on %d"
> >  lockcnt_futex_wait_resume(const void *lockcnt, int new) "lockcnt %p after 
> > wait: %d"
> >  lockcnt_futex_wake(const void *lockcnt) "lockcnt %p waking up one waiter"
> > +
> > +# util/qemu-thread-posix.c
> > +qemu_mutex_lock(void *qemu_global_mutex) "locked mutex %p"
> > +qemu_mutex_unlock(void *qemu_global_mutex) "unlocked mutex %p"
> 
> Parameter name is slightly misleading, maybe s/qemu_global_mutex/lock/ for 
> both
> lines?

Great! I'll change it and send a v2.

Thank for your review!

> 
> Fam
>