On Tue, 2011-05-31 at 18:38 +0200, Gilles Chanteperdrix wrote: > On 05/31/2011 06:29 PM, Philippe Gerum wrote: > > On Tue, 2011-05-31 at 13:37 +0200, Jan Kiszka wrote: > >> Hi Philippe, > >> > >> enabling XENO_OPT_DEBUG_NUCLEUS reveals some shortcomings of the > >> in-kernel lock usage tracking via xnthread_t::hrescnt. This BUGON in > >> xnsynch_release triggers for RT threads: > >> > >> XENO_BUGON(NUCLEUS, xnthread_get_rescnt(lastowner) < 0); > >> > >> RT threads do not balance their lock and unlock syscalls, so their > >> counter goes wild quite quickly. > >> > >> But just limiting the bug check to XNOTHER threads is neither a > >> solution. How to deal with the counter on scheduling policy changes? > >> > >> So my suggestion is to convert the auto-relax feature into a service, > >> user space can request based on a counter that user space maintains > >> independently. I.e. we should create another shared word that user space > >> increments and decrements on lock acquisitions/releases on its own. The > >> nucleus just tests it when deciding about the relax on return to user > >> space. > >> > >> But before hacking into that direction, I'd like to hear if it makes > >> sense to you. > > > > At first glance, this does not seem to address the root issue. The > > bottom line is that we should not have any thread release an owned lock > > it does not hold, kthread or not. > > > > In that respect, xnsynch_release() looks fishy because it may be called > > over a context which is _not_ the lock owner, but the thread who is > > deleting the lock owner, so assuming lastowner == current_thread when > > releasing is wrong. > > > > At the very least, the following patch would prevent > > xnsynch_release_all_ownerships() to break badly. The same way, the > > fastlock stuff does not track the owner properly in the synchro object. > > We should fix those issues before going further, they may be related to > > the bug described. > > It looks to me like xnsynch_fast_release uses cmpxchg, so, will not set > the owner to NULL if the current owner is not the thread releasing the > mutex. Is it not sufficient? >
Yes, we need to move that swap to the irq off section to clear the owner there as well. -- Philippe. _______________________________________________ Xenomai-core mailing list [email protected] https://mail.gna.org/listinfo/xenomai-core
