On Wed, Oct 10, 2018 at 2:29 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote: > On Wed, Oct 10, 2018 at 2:25 PM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: >> On Wed 10-10-18 20:48:33, Sergey Senozhatsky wrote: >>> On (10/10/18 13:35), Michal Hocko wrote: >>> > > Just flooding out of memory messages can trigger RCU stall problems. >>> > > For example, a severe skbuff_head_cache or kmalloc-512 leak bug is causing >>> > >>> > [...] >>> > >>> > Quite some of them, indeed! I guess we want to rate limit the output. >>> > What about the following? >>> >>> A bit unrelated, but while we are at it: >>> >>> I like it when we rate-limit printk-s that lookup the system. >>> But it seems that default rate-limit values are not always good enough, >>> DEFAULT_RATELIMIT_INTERVAL / DEFAULT_RATELIMIT_BURST can still be too >>> verbose. For instance, when we have a very slow IPMI emulated serial >>> console -- e.g. baud rate at 57600. DEFAULT_RATELIMIT_INTERVAL and >>> DEFAULT_RATELIMIT_BURST can add new OOM headers and backtraces faster >>> than we evict them. >>> >>> Does it sound reasonable enough to use larger than default rate-limits >>> for printk-s in OOM print-outs? OOM reports tend to be somewhat large >>> and the reported numbers are not always *very* unique. >>> >>> What do you think? >> >> I do not really care about the current inerval/burst values. This change >> should be done seprately and ideally with some numbers. > > I think Sergey meant that this place may need to use > larger-than-default values because it prints lots of output per > instance (whereas the default limit is more tuned for cases that print > just 1 line). > > I've found at least 1 place that uses DEFAULT_RATELIMIT_INTERVAL*10: > https://elixir.bootlin.com/linux/latest/source/fs/btrfs/extent-tree.c#L8365 > Probably we need something similar here. In parallel with the kernel changes I've also made a change to syzkaller that (1) makes it not use oom_score_adj=-1000, this hard killing limit looks like quite risky thing, (2) increase memcg size beyond expected KASAN quarantine size: https://github.com/google/syzkaller/commit/adedaf77a18f3d03d695723c86fc083c3551ff5b If this will stop the flow of hang/stall reports, then we can just close all old reports as invalid.
