From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Jan Kara <jack@suse.cz>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Petr Mladek <pmladek@suse.cz>, KY Sri nivasan <kys@microsoft.com>,
Steven Rostedt <rostedt@goodmis.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/7] printk: Hand over printing to console if printing too long
Date: Wed, 23 Dec 2015 13:15:46 +0900 [thread overview]
Message-ID: <20151223041546.GD2008@swordfish> (raw)
In-Reply-To: <20151223035732.GC2008@swordfish>
On (12/23/15 12:57), Sergey Senozhatsky wrote:
[..]
> > > can we replace this oops_in_progress check with something more reliable?
> > >
> > > CPU0 CPU1 - CPUN
> > > panic()
> > > local_irq_disable() executing foo() with irqs disabled,
> > > console_verbose() or processing an extremely long irq handler.
> > > bust_spinlocks()
> > > oops_in_progress++
>
> or we huge enough number of CPUs, `deep' stack
> traces, slow serial and CPU doing dump_stack()
> under raw_spin_lock(&stop_lock), so it can take
> longer than 1 second to print the stacks and
> thus panic CPU will set oops_in_progress back
> to 0.
>
> > > smp_send_stop()
> > >
> > > bust_spinlocks()
> > > oops_in_progress-- ok, IPI arrives
> > > dump_stack()/printk()/etc from IPI_CPU_STOP
> > > "while (1) cpu_relax()" with irq/fiq disabled/halt/etc.
> > >
> > > smp_send_stop() wrapped in `oops_in_progress++/oops_in_progress--' is arch specific,
> > > and some platforms don't do any IPI-delivered (e.g. via num_online_cpus()) checks at
> > > all. Some do. For example, arm/arm64:
> > >
> > > void smp_send_stop(void)
> > > ...
> > > /* Wait up to one second for other CPUs to stop */
> > > timeout = USEC_PER_SEC;
> > > while (num_online_cpus() > 1 && timeout--)
> > > udelay(1);
> > >
> > > if (num_online_cpus() > 1)
> > > pr_warn("SMP: failed to stop secondary CPUs\n");
> > > ...
> > >
> > >
> > > so there are non-zero chances that IPI will arrive to CPU after 'oops_in_progress--',
> > > and thus dump_stack()/etc. happening on that/those cpu/cpus will be lost.
> > >
> > >
> > > bust_spinlocks(0) does
> > > ...
> > > if (--oops_in_progress == 0)
> > > wake_up_klogd();
> > > ...
> > >
> > > but local cpu has irqs disabled and `panic_timeout' can be zero.
well, if panic_timeout != 0, then wake_up_klogd() calls irq_work_queue() which
schedule_work. what if we have the following
CPU0 CPU1 - CPUN
foo
preempt_disable
bar
panic irq/fiq disable
schedule_work while (1) cpu_relax
-ss
next prev parent reply other threads:[~2015-12-23 4:14 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-10 14:52 [PATCH 1/7] printk: Hand over printing to console if printing too long Sergey Senozhatsky
2015-12-10 15:24 ` Sergey Senozhatsky
2015-12-11 4:27 ` Sergey Senozhatsky
2015-12-11 6:29 ` Sergey Senozhatsky
2015-12-22 13:47 ` Jan Kara
2015-12-22 14:48 ` Sergey Senozhatsky
2015-12-23 1:54 ` Sergey Senozhatsky
2015-12-23 3:37 ` Sergey Senozhatsky
2015-12-23 3:57 ` Sergey Senozhatsky
2015-12-23 4:15 ` Sergey Senozhatsky [this message]
2016-01-05 14:37 ` Jan Kara
2016-01-06 1:41 ` Sergey Senozhatsky
2016-01-06 6:48 ` Sergey Senozhatsky
2016-01-06 12:25 ` Jan Kara
2016-01-11 13:25 ` Sergey Senozhatsky
2015-12-31 2:44 ` Sergey Senozhatsky
2015-12-31 3:13 ` Sergey Senozhatsky
2015-12-31 4:58 ` Sergey Senozhatsky
2016-01-05 14:48 ` Jan Kara
2016-01-06 3:38 ` Sergey Senozhatsky
2016-01-06 8:36 ` Sergey Senozhatsky
2016-01-06 10:21 ` Jan Kara
2016-01-06 11:10 ` Sergey Senozhatsky
2016-01-11 12:54 ` Petr Mladek
2016-01-12 14:00 ` Jan Kara
-- strict thread matches above, loose matches on Subject: below --
2015-10-26 4:52 [PATCH 0/6 v2] printk: Softlockup avoidance Jan Kara
2015-10-26 4:52 ` [PATCH 1/7] printk: Hand over printing to console if printing too long Jan Kara
2016-03-01 17:22 ` Denys Vlasenko
2016-03-02 9:30 ` Jan Kara
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