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. 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
