From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <53354B73.6030302@xenomai.org> Date: Fri, 28 Mar 2014 11:14:11 +0100 From: Philippe Gerum MIME-Version: 1.0 References: <53316C4C.6000708@sigmatek.at> <53335D9A.9040902@xenomai.org> <5333F22F.70805@xenomai.org> <53345143.7000009@xenomai.org> <53354665.10604@sigmatek.at> In-Reply-To: <53354665.10604@sigmatek.at> 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: erwin.pranz@sigmatek.at, xenomai@xenomai.org On 03/28/2014 10:52 AM, Erwin Pranz wrote: > Am 27.03.2014 17:26, schrieb Philippe Gerum: >> 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, >> > Hello, > > I tried this patch, but it did not compile: > In file included from include/xenomai/nucleus/registry.h:33:0, > from include/xenomai/nucleus/thread.h:160, > from include/xenomai/nucleus/sched.h:31, > from include/xenomai/nucleus/pod.h:34, > from include/xenomai/nucleus/xenomai.h:23, > from include/xenomai/rtdm/rtdm_driver.h:37, > from drivers/xenomai/can/rtcan_internal.h:30, > from drivers/xenomai/can/rtcan_dev.c:32: > include/xenomai/nucleus/synch.h: In function 'xnsynch_try_grab': > include/xenomai/nucleus/synch.h:205:2: error: implicit declaration of > function 'xnthread_test_state' [-Werror=implicit-function-declaration] > include/xenomai/nucleus/synch.h:206:3: error: implicit declaration of > function 'xnthread_inc_rescnt' [-Werror=implicit-function-declaration] > > I think there is a circular dependency problem in the header files: > - thread.h includes sync.h via registry.h at a point before > xnthread_test_state/xnthread_inc_rescnt is defined > - synch.h needs the defines from thread.h > (xnthread_test_state/xnthread_inc_rescnt) > > I could not resolve this dependency > Then let's make this a thread-based helper, this is logically correct too, and there can't be any ambiguity with respect to which kind of resources can be possibly grabbed by a core thread (and this is better than messing up with macros to postpone the references). diff --git a/include/nucleus/thread.h b/include/nucleus/thread.h index 4a740a0..aca5f90 100644 --- a/include/nucleus/thread.h +++ b/include/nucleus/thread.h @@ -436,6 +436,22 @@ struct xnthread *xnthread_lookup(xnhandle_t threadh) return (thread && xnthread_handle(thread) == threadh) ? thread : NULL; } +static inline int xnthread_try_grab(struct xnthread *thread, + struct xnsynch *synch) +{ + 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; +} + #ifdef __cplusplus extern "C" { #endif diff --git a/ksrc/skins/rtdm/drvlib.c b/ksrc/skins/rtdm/drvlib.c index 391d45f..2e0f14b 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 (!xnthread_try_grab(curr_thread, &mutex->synch_base)) { /* Redefinition to clarify XENO_ASSERT output */ #define mutex_owner xnsynch_owner(&mutex->synch_base) XENO_ASSERT(RTDM, mutex_owner != curr_thread, -- Philippe.