linux-kernel - Re: [PATCH] net/skbuff: silence warnings under memory pressure

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Message-ID: <20190904065455.GE3838@dhcp22.suse.cz>
Date:   Wed, 4 Sep 2019 08:54:55 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:     Qian Cai <cai@....pw>, Eric Dumazet <eric.dumazet@...il.com>,
        davem@...emloft.net, netdev@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] net/skbuff: silence warnings under memory pressure

On Wed 04-09-19 15:41:44, Sergey Senozhatsky wrote:
> On (09/04/19 08:15), Michal Hocko wrote:
> > > If you look at the original report, the failed allocation dump_stack() is,
> > > 
> > >  <IRQ>
> > >  warn_alloc.cold.43+0x8a/0x148
> > >  __alloc_pages_nodemask+0x1a5c/0x1bb0
> > >  alloc_pages_current+0x9c/0x110
> > >  allocate_slab+0x34a/0x11f0
> > >  new_slab+0x46/0x70
> > >  ___slab_alloc+0x604/0x950
> > >  __slab_alloc+0x12/0x20
> > >  kmem_cache_alloc+0x32a/0x400
> > >  __build_skb+0x23/0x60
> > >  build_skb+0x1a/0xb0
> > >  igb_clean_rx_irq+0xafc/0x1010 [igb]
> > >  igb_poll+0x4bb/0xe30 [igb]
> > >  net_rx_action+0x244/0x7a0
> > >  __do_softirq+0x1a0/0x60a
> > >  irq_exit+0xb5/0xd0
> > >  do_IRQ+0x81/0x170
> > >  common_interrupt+0xf/0xf
> > >  </IRQ>
> > > 
> > > Since it has no __GFP_NOWARN to begin with, it will call,
> 
> I think that DEFAULT_RATELIMIT_INTERVAL and DEFAULT_RATELIMIT_BURST
> are good when we ratelimit just a single printk() call, so the ratelimit
> is "max 10 kernel log lines in 5 seconds".

I am sorry, I could have been more explicit when CCing you. Sure the
ratelimit is part of the problem. But I was more interested in the
potential livelock (infinite loop) mentioned by Qian Cai. It is not
important whether we generate one or more lines of output from the
softirq context as long as the printk generates more irq processing
which might end up doing the same. Is this really possible?
-- 
Michal Hocko
SUSE Labs