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trace: add qemu mutex lock and unlock trace events

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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>
Message-Id: <1493054398-26013-1-git-send-email-joserz@linux.vnet.ibm.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
[Also handle trylock, cond_wait and win32; trace "unlocked" while still
 in the critical section, so that "unlocked" always comes before the
 next "locked" tracepoint. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Jose Ricardo Ziviani
2017-04-24 14:19:58 -03:00
committed by Paolo Bonzini
parent f68826989c
commit 31f5a726b5
3 changed files with 31 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

18
util/qemu-thread-posix.c
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@@ -14,6 +14,7 @@
#include "qemu/thread.h"
#include "qemu/atomic.h"
#include "qemu/notify.h"
#include "trace.h"
static bool name_threads;
@@ -60,17 +61,30 @@ void qemu_mutex_lock(QemuMutex *mutex)
err = pthread_mutex_lock(&mutex->lock);
if (err)
error_exit(err, __func__);
trace_qemu_mutex_locked(mutex);
}
int qemu_mutex_trylock(QemuMutex *mutex)
{
return pthread_mutex_trylock(&mutex->lock);
int err;
err = pthread_mutex_trylock(&mutex->lock);
if (err == 0) {
trace_qemu_mutex_locked(mutex);
return 0;
}
if (err != EBUSY) {
error_exit(err, __func__);
}
return -EBUSY;
}
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__);
@@ -130,7 +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__);
}