From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <53345143.7000009@xenomai.org> Date: Thu, 27 Mar 2014 17:26:43 +0100 From: Philippe Gerum MIME-Version: 1.0 References: <53316C4C.6000708@sigmatek.at> <53335D9A.9040902@xenomai.org> <5333F22F.70805@xenomai.org> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai] Rescnt imbalance in rtdm_mutex_timedlock List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Henri Roosen Cc: "Xenomai@xenomai.org" On 03/27/2014 04:02 PM, Henri Roosen wrote: > > > > On Thu, Mar 27, 2014 at 10:41 AM, Philippe Gerum > wrote: > > On 03/27/2014 12:07 AM, Gilles Chanteperdrix wrote: > > On 03/26/2014 05:49 PM, Henri Roosen wrote: > > On Tue, Mar 25, 2014 at 12:45 PM, Erwin Pranz > >__wrote: > > Hello, > > I am using rtdm_mutex_lock/rtdm_mutex___unlock in a rtdm > driver and I get a > signal SIGDEBUG_MIGRATE_PRIOINV when I call the driver > from a priority-0 > thread.The signal is sent in xnsynch_release_thread when > rescnt is 0 on a > XNOTHER thread, which means that rescnt is not balanced. > > I think the reason why rescnt is not balanced is in > rtdm_mutex_timedlock: > when the owner of the mutex is NULL, the owner is > changed to the calling > thread, but rescnt is not increased. > > I suggest the following fix in rtdm_mutex_timedlock: > - else if > (likely(xnsynch_owner(&mutex->__synch_base) == NULL)) > + else if > (likely(xnsynch_owner(&mutex->__synch_base) == NULL)) { > > xnsynch_set_owner(&mutex->__synch_base, curr_thread); > + if (xnthread_test_state(curr___thread, > XNOTHER)) > + xnthread_inc_rescnt(curr___thread); > + } > > > Hi Gilles, > > Could you maybe elaborate on this? It seems the resource > counting is not in > balance. It would be great to know if this the correct way > to fix it. > > The problem should be easily reproducible by having just one > shadowed > priority 0 thread that somehow calls rtdm_mutex_lock > directly followed by > rtdm_mutex_unlock. This will trigger the code in > ksrc/nucleus/synch.c that > was added by commit-486afd15, which sends > SIGDEBUG_MIGRATE_PRIOINV on > Xenomai v2.6.2.1. It shouldn't send any signal in that case, > as nothing is > wrong. > > Note we are on Xenomai v2.6.2.1. Xenomai v2.6.3 sends (the > better name for > it) SIGDEBUG_RESCNT_IMBALANCE. > > > To be completely frank, I expected Jan to answer this mail as this > concerns RTDM. Anyway, I had a look into it, and: > - the RTDM skin is not alone in this case, several skins > implement the > same pattern (if owner == NULL, set owner, then return); > - adding calls to xnthread_inc_rescnt everywhere does not seem > right, I > would prefer to move this inside some xnsynch_ service. The best > candidate I found for that is xnsynch_set_owner, though I am not > sure if > this will work, especially with fastsynchs. > > > > Indeed this wouldn't. I suspect the skins mentioned did not have > access to xnsynch_acquire(), and were not updated when the > auto-relax feature was introduced for XNOTHER threads. > > We could provide a helper for fast grabbing a mutex which has no > fast locking support shared with userland, saving a call to > xnsynch_acquire() in the non-contended case, e.g. > > diff --git a/include/nucleus/synch.h b/include/nucleus/synch.h > index 7deae21..87456ea 100644 > --- a/include/nucleus/synch.h > +++ b/include/nucleus/synch.h > @@ -192,6 +192,22 @@ static inline void xnsynch_set_owner(struct > xnsynch *synch, > synch->owner = thread; > } > > +static inline int xnsynch_fast_grab(struct xnsynch *synch, > + struct xnthread *thread) > +{ > + XENO_BUGON(NUCLEUS, xnsynch_fastlock_p(synch)); > + > + if (likely(xnsynch_owner(synch) != NULL)) > + return 0; > + > + xnsynch_set_owner(synch, thread); > + > + if (xnthread_test_state(thread, XNOTHER)) > + xnthread_inc_rescnt(thread); > + > + return 1; > +} > + > static inline void xnsynch_register_cleanup(__struct xnsynch *synch, > void (*handler)(struct > xnsynch *)) > { > diff --git a/ksrc/skins/rtdm/drvlib.c b/ksrc/skins/rtdm/drvlib.c > index 391d45f..338005d 100644 > --- a/ksrc/skins/rtdm/drvlib.c > +++ b/ksrc/skins/rtdm/drvlib.c > @@ -1538,9 +1538,7 @@ int rtdm_mutex_timedlock(rtdm___mutex_t > *mutex, nanosecs_rel_t timeout, > if (unlikely(xnsynch_test_flags(&__mutex->synch_base, > RTDM_SYNCH_DELETED))) > err = -EIDRM; > > - else if (likely(xnsynch_owner(&mutex->__synch_base) == NULL)) > - xnsynch_set_owner(&mutex->__synch_base, curr_thread); > - else { > + else if (!xnsynch_fast_grab(&mutex->__synch_base, > curr_thread)) { > /* Redefinition to clarify XENO_ASSERT output */ > #define mutex_owner xnsynch_owner(&mutex->synch___base) > XENO_ASSERT(RTDM, mutex_owner != curr_thread, > > The VxWorks and VRTX skins would have to use it as well. > > > Thanks for the replies! We'll give this patch a try for the RTDM case. > Minor points, but a compiler hint above was inverted and eventually useless, and the naming not descriptive enough. Take #2: diff --git a/include/nucleus/synch.h b/include/nucleus/synch.h index 7deae21..09ebdbf 100644 --- a/include/nucleus/synch.h +++ b/include/nucleus/synch.h @@ -192,6 +192,22 @@ static inline void xnsynch_set_owner(struct xnsynch *synch, synch->owner = thread; } +static inline int xnsynch_try_grab(struct xnsynch *synch, + struct xnthread *thread) +{ + XENO_BUGON(NUCLEUS, xnsynch_fastlock_p(synch)); + + if (xnsynch_owner(synch) != NULL) + return 0; + + xnsynch_set_owner(synch, thread); + + if (xnthread_test_state(thread, XNOTHER)) + xnthread_inc_rescnt(thread); + + return 1; +} + static inline void xnsynch_register_cleanup(struct xnsynch *synch, void (*handler)(struct xnsynch *)) { diff --git a/ksrc/skins/rtdm/drvlib.c b/ksrc/skins/rtdm/drvlib.c index 391d45f..aa85d11 100644 --- a/ksrc/skins/rtdm/drvlib.c +++ b/ksrc/skins/rtdm/drvlib.c @@ -1538,9 +1538,7 @@ int rtdm_mutex_timedlock(rtdm_mutex_t *mutex, nanosecs_rel_t timeout, if (unlikely(xnsynch_test_flags(&mutex->synch_base, RTDM_SYNCH_DELETED))) err = -EIDRM; - else if (likely(xnsynch_owner(&mutex->synch_base) == NULL)) - xnsynch_set_owner(&mutex->synch_base, curr_thread); - else { + else if (!xnsynch_try_grab(&mutex->synch_base, curr_thread)) { /* Redefinition to clarify XENO_ASSERT output */ #define mutex_owner xnsynch_owner(&mutex->synch_base) XENO_ASSERT(RTDM, mutex_owner != curr_thread, -- Philippe.