From: Qian Cai <cai@lca.pw>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Michal Hocko <mhocko@kernel.org>,
Eric Dumazet <eric.dumazet@gmail.com>,
davem@davemloft.net, netdev@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, Petr Mladek <pmladek@suse.com>,
Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH] net/skbuff: silence warnings under memory pressure
Date: Wed, 04 Sep 2019 11:07:19 -0400 [thread overview]
Message-ID: <1567609639.5576.79.camel@lca.pw> (raw)
In-Reply-To: <20190904144850.GA8296@tigerII.localdomain>
On Wed, 2019-09-04 at 23:48 +0900, Sergey Senozhatsky wrote:
> On (09/04/19 08:14), Qian Cai wrote:
> > > Plus one more check - waitqueue_active(&log_wait). printk() adds
> > > pending irq_work only if there is a user-space process sleeping on
> > > log_wait and irq_work is not already scheduled. If the syslog is
> > > active or there is noone to wakeup then we don't queue irq_work.
> >
> > Another possibility for this potential livelock is that those printk() from
> > warn_alloc(), dump_stack() and show_mem() increase the time it needs to
> > process
> > build_skb() allocation failures significantly under memory pressure. As the
> > result, ksoftirqd() could be rescheduled during that time via a different
> > CPU
> > (this is a large x86 NUMA system anyway),
> >
> > [83605.577256][ C31] run_ksoftirqd+0x1f/0x40
> > [83605.577256][ C31] smpboot_thread_fn+0x255/0x440
> > [83605.577256][ C31] kthread+0x1df/0x200
> > [83605.577256][ C31] ret_from_fork+0x35/0x40
>
> Hum hum hum...
>
> So I can, _probably_, think of several patches.
>
> First, move wake_up_klogd() back to console_unlock().
>
> Second, move `printk_pending' out of per-CPU region and make it global.
> So we will have just one printk irq_work scheduled across all CPUs;
> currently we have one irq_work per CPU. I think I sent a patch a long
> long time ago, but we never discussed it, as far as I remember.
>
> > In addition, those printk() will deal with console drivers or even a
> > networking
> > console, so it is probably not unusual that it could call irq_exit()-
> > __do_softirq() at one point and then this livelock.
>
> Do you use netcon? Because this, theoretically, can open up one more
> vector. netcon allocates skbs from ->write() path. We call con drivers'
> ->write() from printk_safe context, so should netcon skb allocation
> warn we will scedule one more irq_work on that CPU to flush per-CPU
> printk_safe buffer.
No, I don't use netcon. Just thought to mention it anyway since there could
other people use it.
>
> If this is the case, then we can stop calling console_driver() under
> printk_safe. I sent a patch a while ago, but we agreed to keep the
> things the way they are, fot the time being.
>
> Let me think more.
>
> -ss
next prev parent reply other threads:[~2019-09-04 15:07 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-30 14:57 [PATCH] net/skbuff: silence warnings under memory pressure Qian Cai
2019-08-30 15:11 ` Eric Dumazet
2019-08-30 15:25 ` Qian Cai
2019-08-30 16:15 ` Eric Dumazet
2019-08-30 18:06 ` Qian Cai
2019-09-03 13:22 ` Michal Hocko
2019-09-03 15:42 ` Qian Cai
2019-09-03 18:53 ` Michal Hocko
2019-09-03 21:42 ` Qian Cai
2019-09-04 6:15 ` Michal Hocko
2019-09-04 6:41 ` Sergey Senozhatsky
2019-09-04 6:54 ` Michal Hocko
2019-09-04 7:19 ` Sergey Senozhatsky
2019-09-04 7:43 ` Sergey Senozhatsky
2019-09-04 12:14 ` Qian Cai
2019-09-04 14:48 ` Sergey Senozhatsky
2019-09-04 15:07 ` Qian Cai [this message]
2019-09-04 20:42 ` Qian Cai
2019-09-05 8:32 ` Eric Dumazet
2019-09-05 14:09 ` Qian Cai
2019-09-05 15:06 ` Eric Dumazet
2019-09-05 15:14 ` Eric Dumazet
2019-09-05 11:32 ` Sergey Senozhatsky
2019-09-05 16:03 ` Qian Cai
2019-09-05 17:14 ` Steven Rostedt
2019-09-06 2:50 ` Sergey Senozhatsky
2019-09-06 4:32 ` Sergey Senozhatsky
2019-09-06 21:17 ` Qian Cai
2019-09-05 17:23 ` Steven Rostedt
2019-09-06 3:39 ` Sergey Senozhatsky
2019-09-06 15:32 ` Petr Mladek
2019-09-09 1:10 ` Sergey Senozhatsky
2019-09-06 14:55 ` Petr Mladek
2019-09-06 19:51 ` Sergey Senozhatsky
2019-11-14 17:12 ` Qian Cai
2019-11-18 15:27 ` Petr Mladek
2019-11-19 0:41 ` Sergey Senozhatsky
2019-11-19 9:41 ` Petr Mladek
2019-11-19 15:58 ` Qian Cai
2019-11-20 1:30 ` Sergey Senozhatsky
2019-11-20 16:13 ` Petr Mladek
2019-11-21 1:05 ` Sergey Senozhatsky
2019-11-21 9:15 ` Petr Mladek
2019-09-04 7:00 ` Sergey Senozhatsky
2019-09-04 8:25 ` Michal Hocko
2019-09-04 11:59 ` Qian Cai
2019-09-04 12:07 ` Michal Hocko
2019-09-04 12:28 ` Qian Cai
2019-09-07 11:00 ` Tetsuo Handa
2019-09-04 6:15 ` Michal Hocko
2019-09-02 14:24 ` Vlastimil Babka
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