On Thu, 7 Jan 2016, Laura Abbott wrote: > The slub_debug=P not only poisons it enables other consistency checks on the > slab as well, assuming my understanding of what check_object does is correct. > My hope was to have the poison part only and none of the consistency checks in > an attempt to mitigate performance issues. I misunderstood when the checks > actually run and how SLUB_DEBUG was used. Ok I see that there pointer check is done without checking the corresponding debug flag. Patch attached thar fixes it. > Another option would be to have a flag like SLAB_NO_SANITY_CHECK. > sanitization enablement would just be that and SLAB_POISON > in the debug options. The disadvantage to this approach would be losing > the sanitization for ->ctor caches (the grsecurity version works around this > by re-initializing with ->ctor, I haven't heard any feedback if this actually > acceptable) and not having some of the fast paths enabled > (assuming I'm understanding the code path correctly.) which would also > be a performance penalty I think we simply need to fix the missing check there. There is already a flag SLAB_DEBUG_FREE for the pointer checks. Subject: slub: Only perform pointer checks in check_object when SLAB_DEBUG_FREE is set Seems that check_object() always checks for pointer issues currently. Signed-off-by: Christoph Lameter <cl@xxxxxxxxx> Index: linux/mm/slub.c =================================================================== --- linux.orig/mm/slub.c +++ linux/mm/slub.c @@ -848,6 +848,9 @@ static int check_object(struct kmem_cach */ return 1; + if (!(s->flags & SLAB_DEBUG_FREE)) + return 1; + /* Check free pointer validity */ if (!check_valid_pointer(s, page, get_freepointer(s, p))) { object_err(s, page, p, "Freepointer corrupt"); -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>