From: Qian Cai <cai@lca.pw>
To: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@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
Subject: Re: [PATCH] net/skbuff: silence warnings under memory pressure
Date: Thu, 14 Nov 2019 12:12:50 -0500 [thread overview]
Message-ID: <1573751570.5937.122.camel@lca.pw> (raw)
In-Reply-To: <20190905113208.GA521@jagdpanzerIV>
On Thu, 2019-09-05 at 20:32 +0900, Sergey Senozhatsky wrote:
> On (09/04/19 16:42), Qian Cai wrote:
> > > Let me think more.
> >
> > To summary, those look to me are all good long-term improvement that would
> > reduce the likelihood of this kind of livelock in general especially for other
> > unknown allocations that happen while processing softirqs, but it is still up to
> > the air if it fixes it 100% in all situations as printk() is going to take more
> > time
>
> Well. So. I guess that we don't need irq_work most of the time.
>
> We need to queue irq_work for "safe" wake_up_interruptible(), when we
> know that we can deadlock in scheduler. IOW, only when we are invoked
> from the scheduler. Scheduler has printk_deferred(), which tells printk()
> that it cannot do wake_up_interruptible(). Otherwise we can just use
> normal wake_up_process() and don't need that irq_work->wake_up_interruptible()
> indirection. The parts of the scheduler, which by mistake call plain printk()
> from under pi_lock or rq_lock have chances to deadlock anyway and should
> be switched to printk_deferred().
>
> I think we can queue significantly much less irq_work-s from printk().
>
> Petr, Steven, what do you think?
Sergey, do you still plan to get this patch merged?
>
> Something like this. Call wake_up_interruptible(), switch to
> wake_up_klogd() only when called from sched code.
>
> ---
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index cd51aa7d08a9..89cb47882254 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2027,8 +2027,11 @@ asmlinkage int vprintk_emit(int facility, int level,
> pending_output = (curr_log_seq != log_next_seq);
> logbuf_unlock_irqrestore(flags);
>
> + if (!pending_output)
> + return printed_len;
> +
> /* If called from the scheduler, we can not call up(). */
> - if (!in_sched && pending_output) {
> + if (!in_sched) {
> /*
> * Disable preemption to avoid being preempted while holding
> * console_sem which would prevent anyone from printing to
> @@ -2043,10 +2046,11 @@ asmlinkage int vprintk_emit(int facility, int level,
> if (console_trylock_spinning())
> console_unlock();
> preempt_enable();
> - }
>
> - if (pending_output)
> + wake_up_interruptible(&log_wait);
> + } else {
> wake_up_klogd();
> + }
> return printed_len;
> }
> EXPORT_SYMBOL(vprintk_emit);
> ---
>
> > and could deal with console hardware that involve irq_exit() anyway.
>
> printk->console_driver->write() does not involve irq.
>
> > On the other hand, adding __GPF_NOWARN in the build_skb() allocation will fix
> > this known NET_TX_SOFTIRQ case which is common when softirqd involved at least
> > in short-term. It even have a benefit to reduce the overall warn_alloc() noise
> > out there.
>
> That's not up to me to decide.
>
> -ss
next prev parent reply other threads:[~2019-11-14 17:12 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
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 [this message]
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
2019-09-04 6:15 ` Michal Hocko
2019-09-02 14:24 ` Vlastimil Babka
2019-09-03 10:23 ` Qian Cai
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