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 me to see the 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 can 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 <joserz@linux.vnet.ibm.com>
---
v2:
  - removed unecessary (void*) cast
  - renamed parameter name to lock instead of qemu_global_mutex

 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..4f77d7b 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(&mutex->lock);
 }
 
 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(&mutex->lock);
 }
 
 void qemu_rec_mutex_init(QemuRecMutex *mutex)
diff --git a/util/trace-events b/util/trace-events
index b44ef4f..70f6212 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 *lock) "locked mutex %p"
+qemu_mutex_unlock(void *lock) "unlocked mutex %p"
-- 
2.7.4

On Mon, 04/24 14:19, 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 me to see the 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 can 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 <joserz@linux.vnet.ibm.com>
> ---
> v2:
>   - removed unecessary (void*) cast
>   - renamed parameter name to lock instead of qemu_global_mutex
> 
>  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..4f77d7b 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(&mutex->lock);
>  }
>  
>  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(&mutex->lock);
>  }
>  
>  void qemu_rec_mutex_init(QemuRecMutex *mutex)
> diff --git a/util/trace-events b/util/trace-events
> index b44ef4f..70f6212 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 *lock) "locked mutex %p"
> +qemu_mutex_unlock(void *lock) "unlocked mutex %p"
> -- 
> 2.7.4
> 

Reviewed-by: Fam Zheng <famz@redhat.com>

On 24/04/2017 19:19, 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 me to see the 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 can 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 <joserz@linux.vnet.ibm.com>

Some improvements:

1) handle trylock and Win32 too

2) pass mutex instead of &mutex->lock, it is the same but the latter is
unnecessarily obfuscated

3) also trace unlock/lock around cond_wait

4) trace "unlocked" before calling pthread_mutex_unlock, so that it is
always placed before the next "locked" tracepoint.

diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
index bf5756763d..46f4c08e6d 100644
--- a/util/qemu-thread-posix.c
+++ b/util/qemu-thread-posix.c
@@ -62,7 +62,7 @@ void qemu_mutex_lock(QemuMutex *mutex)
     if (err)
         error_exit(err, __func__);

-    trace_qemu_mutex_lock(&mutex->lock);
+    trace_qemu_mutex_locked(mutex);
 }

 int qemu_mutex_trylock(QemuMutex *mutex)
@@ -71,7 +71,7 @@ int qemu_mutex_trylock(QemuMutex *mutex)

     err = pthread_mutex_trylock(&mutex->lock);
     if (err == 0) {
-        trace_qemu_mutex_lock(&mutex->lock);
+        trace_qemu_mutex_locked(mutex);
         return 0;
     }
     if (err == EBUSY) {
@@ -84,11 +84,10 @@ void qemu_mutex_unlock(QemuMutex *mutex)
 {
     int err;

+    trace_qemu_mutex_unlocked(mutex);
     err = pthread_mutex_unlock(&mutex->lock);
     if (err)
         error_exit(err, __func__);
-
-    trace_qemu_mutex_unlock(&mutex->lock);
 }

 void qemu_rec_mutex_init(QemuRecMutex *mutex)
@@ -145,7 +144,9 @@ void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
 {
     int err;

+    trace_qemu_mutex_unlocked(mutex);
     err = pthread_cond_wait(&cond->cond, &mutex->lock);
+    trace_qemu_mutex_locked(mutex);
     if (err)
         error_exit(err, __func__);
 }
diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c
index d3c87bc89e..0dc3ae7756 100644
--- a/util/qemu-thread-win32.c
+++ b/util/qemu-thread-win32.c
@@ -55,6 +55,7 @@ void qemu_mutex_destroy(QemuMutex *mutex)
 void qemu_mutex_lock(QemuMutex *mutex)
 {
     AcquireSRWLockExclusive(&mutex->lock);
+    trace_qemu_mutex_locked(mutex);
 }

 int qemu_mutex_trylock(QemuMutex *mutex)
@@ -64,6 +64,7 @@ int qemu_mutex_trylock(QemuMutex *mutex)

     owned = TryAcquireSRWLockExclusive(&mutex->lock);
     if (owned) {
+        trace_qemu_mutex_locked(mutex);
         return 0;
     }
     return -EBUSY;
@@ -72,6 +72,7 @@ int qemu_mutex_trylock(QemuMutex *mutex)

 void qemu_mutex_unlock(QemuMutex *mutex)
 {
+    trace_qemu_mutex_unlocked(mutex);
     ReleaseSRWLockExclusive(&mutex->lock);
 }

@@ -124,7 +124,9 @@ void qemu_cond_broadcast(QemuCond *cond)

 void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
 {
+    trace_qemu_mutex_unlocked(mutex);
     SleepConditionVariableSRW(&cond->var, &mutex->lock, INFINITE, 0);
+    trace_qemu_mutex_locked(mutex);
 }

 void qemu_sem_init(QemuSemaphore *sem, int init)
diff --git a/util/trace-events b/util/trace-events
index 70f62124e1..fa540c620b 100644
--- a/util/trace-events
+++ b/util/trace-events
@@ -57,5 +57,5 @@ lockcnt_futex_wait_resume(const void *lockcnt, int
new) "lockcnt %p after wait:
 lockcnt_futex_wake(const void *lockcnt) "lockcnt %p waking up one waiter"

 # util/qemu-thread-posix.c
-qemu_mutex_lock(void *lock) "locked mutex %p"
-qemu_mutex_unlock(void *lock) "unlocked mutex %p"
+qemu_mutex_locked(void *lock) "locked mutex %p"
+qemu_mutex_unlocked(void *lock) "unlocked mutex %p"

On Thu, Apr 27, 2017 at 10:55:04AM +0200, Paolo Bonzini wrote:
> 
> 
> On 24/04/2017 19:19, 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 me to see the 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 can 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 <joserz@linux.vnet.ibm.com>
> 
> Some improvements:
> 
> 1) handle trylock and Win32 too
> 
> 2) pass mutex instead of &mutex->lock, it is the same but the latter is
> unnecessarily obfuscated
> 
> 3) also trace unlock/lock around cond_wait
> 
> 4) trace "unlocked" before calling pthread_mutex_unlock, so that it is
> always placed before the next "locked" tracepoint.

I'm working on it
Thanks for your review!

> 
> diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
> index bf5756763d..46f4c08e6d 100644
> --- a/util/qemu-thread-posix.c
> +++ b/util/qemu-thread-posix.c
> @@ -62,7 +62,7 @@ void qemu_mutex_lock(QemuMutex *mutex)
>      if (err)
>          error_exit(err, __func__);
> 
> -    trace_qemu_mutex_lock(&mutex->lock);
> +    trace_qemu_mutex_locked(mutex);
>  }
> 
>  int qemu_mutex_trylock(QemuMutex *mutex)
> @@ -71,7 +71,7 @@ int qemu_mutex_trylock(QemuMutex *mutex)
> 
>      err = pthread_mutex_trylock(&mutex->lock);
>      if (err == 0) {
> -        trace_qemu_mutex_lock(&mutex->lock);
> +        trace_qemu_mutex_locked(mutex);
>          return 0;
>      }
>      if (err == EBUSY) {
> @@ -84,11 +84,10 @@ void qemu_mutex_unlock(QemuMutex *mutex)
>  {
>      int err;
> 
> +    trace_qemu_mutex_unlocked(mutex);
>      err = pthread_mutex_unlock(&mutex->lock);
>      if (err)
>          error_exit(err, __func__);
> -
> -    trace_qemu_mutex_unlock(&mutex->lock);
>  }
> 
>  void qemu_rec_mutex_init(QemuRecMutex *mutex)
> @@ -145,7 +144,9 @@ void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
>  {
>      int err;
> 
> +    trace_qemu_mutex_unlocked(mutex);
>      err = pthread_cond_wait(&cond->cond, &mutex->lock);
> +    trace_qemu_mutex_locked(mutex);
>      if (err)
>          error_exit(err, __func__);
>  }
> diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c
> index d3c87bc89e..0dc3ae7756 100644
> --- a/util/qemu-thread-win32.c
> +++ b/util/qemu-thread-win32.c
> @@ -55,6 +55,7 @@ void qemu_mutex_destroy(QemuMutex *mutex)
>  void qemu_mutex_lock(QemuMutex *mutex)
>  {
>      AcquireSRWLockExclusive(&mutex->lock);
> +    trace_qemu_mutex_locked(mutex);
>  }
> 
>  int qemu_mutex_trylock(QemuMutex *mutex)
> @@ -64,6 +64,7 @@ int qemu_mutex_trylock(QemuMutex *mutex)
> 
>      owned = TryAcquireSRWLockExclusive(&mutex->lock);
>      if (owned) {
> +        trace_qemu_mutex_locked(mutex);
>          return 0;
>      }
>      return -EBUSY;
> @@ -72,6 +72,7 @@ int qemu_mutex_trylock(QemuMutex *mutex)
> 
>  void qemu_mutex_unlock(QemuMutex *mutex)
>  {
> +    trace_qemu_mutex_unlocked(mutex);
>      ReleaseSRWLockExclusive(&mutex->lock);
>  }
> 
> @@ -124,7 +124,9 @@ void qemu_cond_broadcast(QemuCond *cond)
> 
>  void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
>  {
> +    trace_qemu_mutex_unlocked(mutex);
>      SleepConditionVariableSRW(&cond->var, &mutex->lock, INFINITE, 0);
> +    trace_qemu_mutex_locked(mutex);
>  }
> 
>  void qemu_sem_init(QemuSemaphore *sem, int init)
> diff --git a/util/trace-events b/util/trace-events
> index 70f62124e1..fa540c620b 100644
> --- a/util/trace-events
> +++ b/util/trace-events
> @@ -57,5 +57,5 @@ lockcnt_futex_wait_resume(const void *lockcnt, int
> new) "lockcnt %p after wait:
>  lockcnt_futex_wake(const void *lockcnt) "lockcnt %p waking up one waiter"
> 
>  # util/qemu-thread-posix.c
> -qemu_mutex_lock(void *lock) "locked mutex %p"
> -qemu_mutex_unlock(void *lock) "unlocked mutex %p"
> +qemu_mutex_locked(void *lock) "locked mutex %p"
> +qemu_mutex_unlocked(void *lock) "unlocked mutex %p"
> 

----- Original Message -----
> From: joserz@linux.vnet.ibm.com
> To: "Paolo Bonzini" <pbonzini@redhat.com>
> Cc: famz@redhat.com, qemu-devel@nongnu.org, stefanha@redhat.com
> Sent: Thursday, April 27, 2017 4:59:26 PM
> Subject: Re: [Qemu-devel] [PATCH v2] trace: add qemu mutex lock and unlock trace events
> 
> On Thu, Apr 27, 2017 at 10:55:04AM +0200, Paolo Bonzini wrote:
> > 
> > 
> > On 24/04/2017 19:19, 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 me to see the 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 can 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 <joserz@linux.vnet.ibm.com>
> > 
> > Some improvements:
> > 
> > 1) handle trylock and Win32 too
> > 
> > 2) pass mutex instead of &mutex->lock, it is the same but the latter is
> > unnecessarily obfuscated
> > 
> > 3) also trace unlock/lock around cond_wait
> > 
> > 4) trace "unlocked" before calling pthread_mutex_unlock, so that it is
> > always placed before the next "locked" tracepoint.
> 
> I'm working on it
> Thanks for your review!

No need, if you agree with the change below I can just queue the modified
patch.

Paolo

> > 
> > diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
> > index bf5756763d..46f4c08e6d 100644
> > --- a/util/qemu-thread-posix.c
> > +++ b/util/qemu-thread-posix.c
> > @@ -62,7 +62,7 @@ void qemu_mutex_lock(QemuMutex *mutex)
> >      if (err)
> >          error_exit(err, __func__);
> > 
> > -    trace_qemu_mutex_lock(&mutex->lock);
> > +    trace_qemu_mutex_locked(mutex);
> >  }
> > 
> >  int qemu_mutex_trylock(QemuMutex *mutex)
> > @@ -71,7 +71,7 @@ int qemu_mutex_trylock(QemuMutex *mutex)
> > 
> >      err = pthread_mutex_trylock(&mutex->lock);
> >      if (err == 0) {
> > -        trace_qemu_mutex_lock(&mutex->lock);
> > +        trace_qemu_mutex_locked(mutex);
> >          return 0;
> >      }
> >      if (err == EBUSY) {
> > @@ -84,11 +84,10 @@ void qemu_mutex_unlock(QemuMutex *mutex)
> >  {
> >      int err;
> > 
> > +    trace_qemu_mutex_unlocked(mutex);
> >      err = pthread_mutex_unlock(&mutex->lock);
> >      if (err)
> >          error_exit(err, __func__);
> > -
> > -    trace_qemu_mutex_unlock(&mutex->lock);
> >  }
> > 
> >  void qemu_rec_mutex_init(QemuRecMutex *mutex)
> > @@ -145,7 +144,9 @@ void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
> >  {
> >      int err;
> > 
> > +    trace_qemu_mutex_unlocked(mutex);
> >      err = pthread_cond_wait(&cond->cond, &mutex->lock);
> > +    trace_qemu_mutex_locked(mutex);
> >      if (err)
> >          error_exit(err, __func__);
> >  }
> > diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c
> > index d3c87bc89e..0dc3ae7756 100644
> > --- a/util/qemu-thread-win32.c
> > +++ b/util/qemu-thread-win32.c
> > @@ -55,6 +55,7 @@ void qemu_mutex_destroy(QemuMutex *mutex)
> >  void qemu_mutex_lock(QemuMutex *mutex)
> >  {
> >      AcquireSRWLockExclusive(&mutex->lock);
> > +    trace_qemu_mutex_locked(mutex);
> >  }
> > 
> >  int qemu_mutex_trylock(QemuMutex *mutex)
> > @@ -64,6 +64,7 @@ int qemu_mutex_trylock(QemuMutex *mutex)
> > 
> >      owned = TryAcquireSRWLockExclusive(&mutex->lock);
> >      if (owned) {
> > +        trace_qemu_mutex_locked(mutex);
> >          return 0;
> >      }
> >      return -EBUSY;
> > @@ -72,6 +72,7 @@ int qemu_mutex_trylock(QemuMutex *mutex)
> > 
> >  void qemu_mutex_unlock(QemuMutex *mutex)
> >  {
> > +    trace_qemu_mutex_unlocked(mutex);
> >      ReleaseSRWLockExclusive(&mutex->lock);
> >  }
> > 
> > @@ -124,7 +124,9 @@ void qemu_cond_broadcast(QemuCond *cond)
> > 
> >  void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
> >  {
> > +    trace_qemu_mutex_unlocked(mutex);
> >      SleepConditionVariableSRW(&cond->var, &mutex->lock, INFINITE, 0);
> > +    trace_qemu_mutex_locked(mutex);
> >  }
> > 
> >  void qemu_sem_init(QemuSemaphore *sem, int init)
> > diff --git a/util/trace-events b/util/trace-events
> > index 70f62124e1..fa540c620b 100644
> > --- a/util/trace-events
> > +++ b/util/trace-events
> > @@ -57,5 +57,5 @@ lockcnt_futex_wait_resume(const void *lockcnt, int
> > new) "lockcnt %p after wait:
> >  lockcnt_futex_wake(const void *lockcnt) "lockcnt %p waking up one waiter"
> > 
> >  # util/qemu-thread-posix.c
> > -qemu_mutex_lock(void *lock) "locked mutex %p"
> > -qemu_mutex_unlock(void *lock) "unlocked mutex %p"
> > +qemu_mutex_locked(void *lock) "locked mutex %p"
> > +qemu_mutex_unlocked(void *lock) "unlocked mutex %p"
> > 
> 
> 
> 

On Thu, Apr 27, 2017 at 11:59:26AM -0300, joserz@linux.vnet.ibm.com wrote:
> On Thu, Apr 27, 2017 at 10:55:04AM +0200, Paolo Bonzini wrote:
> > 
> > 
> > On 24/04/2017 19:19, 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 me to see the 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 can 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 <joserz@linux.vnet.ibm.com>
> > 
> > Some improvements:
> > 
> > 1) handle trylock and Win32 too
> > 
> > 2) pass mutex instead of &mutex->lock, it is the same but the latter is
> > unnecessarily obfuscated
> > 
> > 3) also trace unlock/lock around cond_wait
> > 
> > 4) trace "unlocked" before calling pthread_mutex_unlock, so that it is
> > always placed before the next "locked" tracepoint.
> 
> I'm working on it
> Thanks for your review!

Ops! just saw you already did it. Thanks.

Reviewed-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
> 
> > 
> > diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
> > index bf5756763d..46f4c08e6d 100644
> > --- a/util/qemu-thread-posix.c
> > +++ b/util/qemu-thread-posix.c
> > @@ -62,7 +62,7 @@ void qemu_mutex_lock(QemuMutex *mutex)
> >      if (err)
> >          error_exit(err, __func__);
> > 
> > -    trace_qemu_mutex_lock(&mutex->lock);
> > +    trace_qemu_mutex_locked(mutex);
> >  }
> > 
> >  int qemu_mutex_trylock(QemuMutex *mutex)
> > @@ -71,7 +71,7 @@ int qemu_mutex_trylock(QemuMutex *mutex)
> > 
> >      err = pthread_mutex_trylock(&mutex->lock);
> >      if (err == 0) {
> > -        trace_qemu_mutex_lock(&mutex->lock);
> > +        trace_qemu_mutex_locked(mutex);
> >          return 0;
> >      }
> >      if (err == EBUSY) {
> > @@ -84,11 +84,10 @@ void qemu_mutex_unlock(QemuMutex *mutex)
> >  {
> >      int err;
> > 
> > +    trace_qemu_mutex_unlocked(mutex);
> >      err = pthread_mutex_unlock(&mutex->lock);
> >      if (err)
> >          error_exit(err, __func__);
> > -
> > -    trace_qemu_mutex_unlock(&mutex->lock);
> >  }
> > 
> >  void qemu_rec_mutex_init(QemuRecMutex *mutex)
> > @@ -145,7 +144,9 @@ void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
> >  {
> >      int err;
> > 
> > +    trace_qemu_mutex_unlocked(mutex);
> >      err = pthread_cond_wait(&cond->cond, &mutex->lock);
> > +    trace_qemu_mutex_locked(mutex);
> >      if (err)
> >          error_exit(err, __func__);
> >  }
> > diff --git a/util/qemu-thread-win32.c b/util/qemu-thread-win32.c
> > index d3c87bc89e..0dc3ae7756 100644
> > --- a/util/qemu-thread-win32.c
> > +++ b/util/qemu-thread-win32.c
> > @@ -55,6 +55,7 @@ void qemu_mutex_destroy(QemuMutex *mutex)
> >  void qemu_mutex_lock(QemuMutex *mutex)
> >  {
> >      AcquireSRWLockExclusive(&mutex->lock);
> > +    trace_qemu_mutex_locked(mutex);
> >  }
> > 
> >  int qemu_mutex_trylock(QemuMutex *mutex)
> > @@ -64,6 +64,7 @@ int qemu_mutex_trylock(QemuMutex *mutex)
> > 
> >      owned = TryAcquireSRWLockExclusive(&mutex->lock);
> >      if (owned) {
> > +        trace_qemu_mutex_locked(mutex);
> >          return 0;
> >      }
> >      return -EBUSY;
> > @@ -72,6 +72,7 @@ int qemu_mutex_trylock(QemuMutex *mutex)
> > 
> >  void qemu_mutex_unlock(QemuMutex *mutex)
> >  {
> > +    trace_qemu_mutex_unlocked(mutex);
> >      ReleaseSRWLockExclusive(&mutex->lock);
> >  }
> > 
> > @@ -124,7 +124,9 @@ void qemu_cond_broadcast(QemuCond *cond)
> > 
> >  void qemu_cond_wait(QemuCond *cond, QemuMutex *mutex)
> >  {
> > +    trace_qemu_mutex_unlocked(mutex);
> >      SleepConditionVariableSRW(&cond->var, &mutex->lock, INFINITE, 0);
> > +    trace_qemu_mutex_locked(mutex);
> >  }
> > 
> >  void qemu_sem_init(QemuSemaphore *sem, int init)
> > diff --git a/util/trace-events b/util/trace-events
> > index 70f62124e1..fa540c620b 100644
> > --- a/util/trace-events
> > +++ b/util/trace-events
> > @@ -57,5 +57,5 @@ lockcnt_futex_wait_resume(const void *lockcnt, int
> > new) "lockcnt %p after wait:
> >  lockcnt_futex_wake(const void *lockcnt) "lockcnt %p waking up one waiter"
> > 
> >  # util/qemu-thread-posix.c
> > -qemu_mutex_lock(void *lock) "locked mutex %p"
> > -qemu_mutex_unlock(void *lock) "unlocked mutex %p"
> > +qemu_mutex_locked(void *lock) "locked mutex %p"
> > +qemu_mutex_unlocked(void *lock) "unlocked mutex %p"
> >