On 05/15/2013 08:01 PM, Kai Bollue wrote: > On 09.05.2013 18:31, Gilles Chanteperdrix wrote: >> On 05/09/2013 06:13 PM, Gilles Chanteperdrix wrote: >> >>> On 05/02/2013 08:45 PM, Kai Bollue wrote: >>> >>>> Hello, >>>> >>>> we experience a crash upon unbinding of a previously deleted (and >>>> cleaned up) shared heap. >>>> Scheme: >>>> - Process A calls rt_heap_create() (with H_SHARED flag), waits for some >>>> time and then terminates. >>>> - Process B calls rt_heap_bind() on that heap, uses it and calls >>>> rt_heap_unbind() (or terminates) after process A has terminated. >>>> >>>> Then the system crashes after the output of "Xenomai: removing >>>> non-linked element, holder=ffffc900125e4940, qslot=ffff880427aa90f8 at >>>> kernel/xenomai/skins/native/heap.c:374". >>>> >>>> The crash does not always happen, but can quite reliably be reproduced >>>> by starting process A in a loop from bash (while [ TRUE ]; do ...) and >>>> keeping process B running. >>>> >>>> Two aspects seem to be crucial: >>>> - Calling rt_heap_delete() in process A is not sufficient to reproduce >>>> the problem, the process has to terminate (the cleaning up seems to be >>>> relevant). >>>> - We could only reproduce the crash as long as process B accessed the >>>> heap after process A had terminated (e.g. using memcpy). >>>> >>>> As a workaround, it could be tried to avoid access to a deleted heap, >>>> but it is not always possible to detect the termination of process A on >>>> time in such a constellation. >>>> >>>> The system: >>>> - AMD AM3 FX-8350 >>>> - Debian 6.0 >>>> - Kernel 3.5.7 >>>> - Xenomai 2.6.2.1 >>>> >>>> We also tested this on an older system (Xenomai 2.6.0, Kernel 2.6.37): >>>> Here, both processes hung indefinitely and could not be killed, but the >>>> system did not crash. >>>> >>>> Any hints are appreciated. >>>> >>>> Attachments: >>>> - Console output >>>> - Code of process A >>>> - Code of process B >>> >>> Hi Kai, >>> >>> thank you very much for your test case, it allowed to reproduce the >>> issue and try and understand what happens. >>> >>> From what I understand, processA creates the shared heap which is added >>> to the list of the objects it holds (xeno_get_rholder()), when processA >>> dies, the heap is removed from the list, but not destroyed because it is >>> also bound to processB. >>> >>> Then processB unbinds the heap, which triggers an auto-destruction, >>> which tries to remove the heap from processA list again. If processA >>> control block has not been re-used, this works, because the list is >>> still there, if processA has be re-launched, the control block has been >>> reinitialized, as well as the list, so removing the element from the >>> list fails. > > Hi Gilles, > > thank you very much for your analysis and suggestions. > >>> I see several possible corrections: >>> - get rt_heap_delete to return an error when the heap is currently bound >>> to another process (EBUSY for instance), while still unmapping it from >>> the current process. This will cause __xeno_flush_rq to move the heap to >>> the "global" ressource holder, where it can safely be deleted later > > I am not sure if this is the best solution as the the heap object itself > can actually be deleted, only the underlying xnheap remains. > >>> - put any rt_heap with the H_MAPPABLE flag directly on the global >>> ressource holder, as it is a global object anyway, this means that when >>> a process which created a mappable heap dies, the heap survives, but >>> this is maybe what should be expected from shareable heaps. > > This is probably better, but: > >> >> - or remove the rt_heap from the list directly in rt_heap_delete, it >> does not seem to make sense to keep it in the list after it has been >> deleted: it will be automatically deleted when the last process bound to >> it unbinds it anyway. >> > > This is IMHO the most consistent solution. With the following change, we > cannot reproduce the crash anymore: > > diff --git a/ksrc/skins/native/heap.c b/ksrc/skins/native/heap.c > index 4a39d07..be4aee9 100644 > --- a/ksrc/skins/native/heap.c > +++ b/ksrc/skins/native/heap.c > @@ -371,8 +371,6 @@ static void __heap_post_release(struct xnheap *h) > > xnlock_get_irqsave(&nklock, s); > > - removeq(heap->rqueue, &heap->rlink); > - > if (heap->handle) > xnregistry_remove(heap->handle); > > @@ -442,6 +440,8 @@ int rt_heap_delete_inner(RT_HEAP *heap, void __user > *mapaddr) > > xeno_mark_deleted(heap); > > + removeq(heap->rqueue, &heap->rlink); > + > /* Get out of the nklocked section before releasing the heap > memory, since we are about to invoke Linux kernel
> services. */ Yes, this is the fix I pushed: http://git.xenomai.org/?p=xenomai-2.6.git;a=commitdiff;h=ee28ad6936964ebf4198dcfd77dec4b8c5e8623c;hp=a2a6d456b23b9960f46964505668619b90b69400 -- Gilles. _______________________________________________ Xenomai mailing list [email protected] http://www.xenomai.org/mailman/listinfo/xenomai
