On 12/04/2015 07:55 AM, Marcelo Ricardo Leitner wrote: > On Fri, Dec 04, 2015 at 11:40:02AM +0100, Dmitry Vyukov wrote: >> On Thu, Dec 3, 2015 at 9:51 PM, Joe Perches <joe@xxxxxxxxxxx> wrote: >>> (adding lkml as this is likely better discussed there) >>> >>> On Thu, 2015-12-03 at 15:42 -0500, Jason Baron wrote: >>>> On 12/03/2015 03:24 PM, Joe Perches wrote: >>>>> On Thu, 2015-12-03 at 15:10 -0500, Jason Baron wrote: >>>>>> On 12/03/2015 03:03 PM, Joe Perches wrote: >>>>>>> On Thu, 2015-12-03 at 14:32 -0500, Jason Baron wrote: >>>>>>>> On 12/03/2015 01:52 PM, Aaron Conole wrote: >>>>>>>>> I think that as a minimum, the following patch should be evaluted, >>>>>>>>> but am unsure to whom I should submit it (after I test): >>>>>>> [] >>>>>>>> Agreed - the intention here is certainly to have no side effects. It >>>>>>>> looks like 'no_printk()' is used in quite a few other places that would >>>>>>>> benefit from this change. So we probably want a generic >>>>>>>> 'really_no_printk()' macro. >>>>>>> >>>>>>> https://lkml.org/lkml/2012/6/17/231 >>>>>> >>>>>> I don't see this in the tree. >>>>> >>>>> It never got applied. >>>>> >>>>>> Also maybe we should just convert >>>>>> no_printk() to do what your 'eliminated_printk()'. >>>>> >>>>> Some of them at least. >>>>> >>>>>> So we can convert all users with this change? >>>>> >>>>> I don't think so, I think there are some >>>>> function evaluation/side effects that are >>>>> required. I believe some do hardware I/O. >>>>> >>>>> It'd be good to at least isolate them. >>>>> >>>>> I'm not sure how to find them via some >>>>> automated tool/mechanism though. >>>>> >>>>> I asked Julia Lawall about it once in this >>>>> thread: https://lkml.org/lkml/2014/12/3/696 >>>>> >>>> >>>> Seems rather fragile to have side effects that we rely >>>> upon hidden in a printk(). >>> >>> Yup. >>> >>>> Just convert them and see what breaks :) >>> >>> I appreciate your optimism. It's very 1995. >>> Try it and see what happens. >> >> >> Whatever is the resolution for pr_debug, we still need to fix this >> particular use-after-free. It affects stability of debug builds, gives >> invalid debug output, prevents us from finding more bugs in SCTP. And >> maybe somebody uses CONFIG_DYNAMIC_DEBUG in production. > > Agreed. I'm already working on a fix for this particular use-after-free. > > Another interesting thing about this is that sctp_do_sm() is called for > nearly every movement that happens on a sctp socket. Said that, that > always-running IDR search hidden on that debug statement do have some > nasty performance impact, specially because it's serialized on a > spinlock. YUCK! I didn't really pay much attention to those debug macros before, but debug_post_sfx() is truly awful. This wasn't such a bad thing where these macros depended on CONFIG_SCTP_DEBUG, but now that they are always built, we need fix them. -vlad > This wouldn't be happening if it was fully ellided and would > be ok if that pr_debug() was really being printed, but not as it is. > Kudos to this report that I could notice this. I'm trying to fix this on > SCTP-side as well. > > Marcelo > -- To unsubscribe from this list: send the line "unsubscribe linux-sctp" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
