linux-kernel - Re: INFO: rcu detected stall in shmem

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Date:   Wed, 10 Oct 2018 14:25:39 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        syzbot <syzbot+77e6b28a7a7106ad0def@...kaller.appspotmail.com>,
        hannes@...xchg.org, akpm@...ux-foundation.org, guro@...com,
        kirill.shutemov@...ux.intel.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, rientjes@...gle.com,
        syzkaller-bugs@...glegroups.com, yang.s@...baba-inc.com,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>
Subject: Re: INFO: rcu detected stall in shmem_fault

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.
-- 
Michal Hocko
SUSE Labs