From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <5333F22F.70805@xenomai.org> Date: Thu, 27 Mar 2014 10:41:03 +0100 From: Philippe Gerum MIME-Version: 1.0 References: <53316C4C.6000708@sigmatek.at> <53335D9A.9040902@xenomai.org> In-Reply-To: <53335D9A.9040902@xenomai.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed 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: Gilles Chanteperdrix , Henri Roosen Cc: "Xenomai@xenomai.org" 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. -- Philippe.