On Mon, 2009-11-02 at 17:41 +0100, Jan Kiszka wrote: > Philippe Gerum wrote: > > On Sat, 2009-10-24 at 19:22 +0200, Philippe Gerum wrote: > >> On Tue, 2009-10-20 at 13:37 +0200, Jan Kiszka wrote: > >>> Allowing xnheap_delete_mapped to return an error and then attempting to > >>> recover from it does not work out very well: Corner cases are racy, > >>> intransparent to the user, and proper error handling imposes a lot of > >>> complexity on the caller - if it actually bothers to check the return > >>> value... > >>> > >>> Fortunately, there is no reason for this function to fail: If the heap > >>> is still mapped, just install the provide cleanup handler and switch to > >>> deferred removal. If the unmapping fails, we either raced with some > >>> other caller of unmap or user space provided a bogus address, or > >>> something else is wrong. In any case, leaving the cleanup callback > >>> behind is the best we can do anyway. > >>> > >>> Removing the return value immediately allows to simplify the callers, > >>> namemly rt_queue_delete and rt_heap_delete. > >>> > >>> Note: This is still not 100% waterproof. If we issue > >>> xnheap_destroy_mapped from module cleanup passing a release handler > >>> that belongs to the module text, deferred release will cause a crash. > >>> But this corner case is no new regression, so let's keep the head in the > >>> sand. > >> I agree with this one, eventually. This does make things clearer, and > >> removes some opportunities for the upper interfaces to shot themselves > >> in the foot. Merged, thanks. > > > > Well, actually, it does make things clearer, but it is broken. Enabling > > list debugging makes the nucleus pull the break after a double unlink in > > vmclose(). > > > > Basically, the issue is that calling rt_queue/heap_delete() explicitly > > from userland will break, due to the vmclose() handler being indirectly > > called by do_munmap() for the last mapping. The nasty thing is that > > without debugs on, kheapq is just silently trashed. > > > > Fix is on its way, along with nommu support for shared heaps as well. > > OK, I see. Just on minor add-on to your fix: > > diff --git a/ksrc/nucleus/heap.c b/ksrc/nucleus/heap.c > index ec14f73..1ae6af6 100644 > --- a/ksrc/nucleus/heap.c > +++ b/ksrc/nucleus/heap.c > @@ -1241,6 +1241,7 @@ void xnheap_destroy_mapped(xnheap_t *heap, > down_write(¤t->mm->mmap_sem); > heap->archdep.release = NULL; > do_munmap(current->mm, (unsigned long)mapaddr, len); > + heap->archdep.release = release; > up_write(¤t->mm->mmap_sem); > } > > @@ -1252,7 +1253,6 @@ void xnheap_destroy_mapped(xnheap_t *heap, > if (heap->archdep.numaps > 0) { > /* The release handler is supposed to clean up the rest. */ > XENO_ASSERT(NUCLEUS, release != NULL, /* nop */); > - heap->archdep.release = release; > return; > } > > > This is safer than leaving a potential race window open between dropping > mmap_sem and fixing up archdep.release again. >
Actually, we have to hold the kheap lock, in case weird code starts mapping randomly from userland without getting a valid descriptor through a skin call. > Jan > -- Philippe. _______________________________________________ Xenomai-core mailing list Xenomai-core@gna.org https://mail.gna.org/listinfo/xenomai-core