On Thu, Aug 05, 2021 at 03:43:11PM +0200, Peter Krempa wrote:
> On Thu, Aug 05, 2021 at 15:08:50 +0200, Tim Wiederhake wrote:
> > `pthread_mutex_destroy`, `pthread_mutex_lock` and `pthread_mutex_unlock`
> > return an error code that is currently ignored.
> >
> > Add debug information if one of these operations failed, e.g. when there
> > is an attempt to destroy a still locked mutex or unlock and already
> > unlocked mutex.
> >
> > Signed-off-by: Tim Wiederhake <twiederh@xxxxxxxxxx>
> > ---
> > src/util/virthread.c | 15 ++++++++++++---
> > 1 file changed, 12 insertions(+), 3 deletions(-)
> >
> > diff --git a/src/util/virthread.c b/src/util/virthread.c
> > index e89c1a09fb..f64dbee9e9 100644
> > --- a/src/util/virthread.c
> > +++ b/src/util/virthread.c
> > @@ -35,7 +35,10 @@
> >
> > #include "viralloc.h"
> > #include "virthreadjob.h"
> > +#include "virlog.h"
> >
> > +#define VIR_FROM_THIS VIR_FROM_THREAD
> > +VIR_LOG_INIT("util.thread");
> >
> > int virOnce(virOnceControl *once, virOnceFunc init)
> > {
> > @@ -83,17 +86,23 @@ int virMutexInitRecursive(virMutex *m)
> >
> > void virMutexDestroy(virMutex *m)
> > {
> > - pthread_mutex_destroy(&m->lock);
> > + if (pthread_mutex_destroy(&m->lock)) {
> > + VIR_WARN("Failed to destroy mutex=%p", m);
> > + }
> > }
> >
> > void virMutexLock(virMutex *m)
> > {
> > - pthread_mutex_lock(&m->lock);
> > + if (pthread_mutex_lock(&m->lock)) {
> > + VIR_WARN("Failed to lock mutex=%p", m);
> > + }
> > }
> >
> > void virMutexUnlock(virMutex *m)
> > {
> > - pthread_mutex_unlock(&m->lock);
> > + if (pthread_mutex_unlock(&m->lock)) {
> > + VIR_WARN("Failed to unlock mutex=%p", m);
> > + }
> > }
>
> I'm not very persuaded that this is a good idea:
>
> 1) The warning itself is not useful
>
> The pointer itself is valid only when the program is running, having
> this in the logs has almost no value.
>
> 2) It spams logs
>
> As noted above, by getting just the log you don't get any useful
> information and users tend to report that log is being spammed in
> certain cases, so while this would note that there is something going
> on a lot of additional work is required to figure out what, thus the
> value of such entry is rather low.
>
> 3) It can create an endless loop
>
> VIR_WARN -> VIR_WARN_INT -> virLogMessage -> virLogVMessage ->
> virLogLock -> virMutexLock()
I think we could use perror() to make it more useful and avoid
the loop
void virMutexDestroy(virMutex *m)
{
if ((errno = pthread_mutex_destroy(&m->lock)) != 0) {
perror("pthread_mutex_destroy");
}
}
still not going to be enough to diagnose the problem fro the
logs though, as we have no use context.
This change would give a bit more of a fighting chance at diagnosis:
in virthread.h
#define virMutexDestroy(m) \
virMutexDestroyImpl(m, __FILE__, __func__, __LINE__)
void virMutexDestroyImpl(virMutex *mm, const char *file, const char *func, int line);
and in virthread.c
void virMutexDestroyImpl(virMutex *m, const char *file, const char *func, int line)
{
if ((errno = pthread_mutex_destroy(&m->lock)) != 0) {
g_autofree char *msg = g_strdup_printf("pthread_mutex_destroy (caller %s in %s:%d)",
func, file, line);
perror(msg);
}
}
That results in:
$ ./build/tests/qemusecuritytest
TEST: qemusecuritytest
pthread_mutex_destroy (caller virObjectLockableDispose in ../src/util/virobject.c:349): Device or resource busy
!pthread_mutex_destroy (caller virObjectLockableDispose in ../src/util/virobject.c:349): Device or resource busy
!pthread_mutex_destroy (caller virObjectLockableDispose in ../src/util/virobject.c:349): Device or resource busy
!pthread_mutex_destroy (caller virObjectLockableDispose in ../src/util/virobject.c:349): Device or resource busy
!pthread_mutex_destroy (caller virObjectLockableDispose in ../src/util/virobject.c:349): Device or resource busy
!pthread_mutex_destroy (caller virObjectLockableDispose in ../src/util/virobject.c:349): Device or resource busy
Regards,
Daniel
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