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? -- Gilles. _______________________________________________ Xenomai-core mailing list Xenomaiemail@example.com https://mail.gna.org/listinfo/xenomai-core