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From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Petr Mladek <pmladek@suse.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	John Ogness <john.ogness@linutronix.de>,
	Petr Tesarik <ptesarik@suse.cz>,
	Konstantin Khlebnikov <koct9i@gmail.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] printk/panic: Access the main printk log in panic() only when safe
Date: Thu, 18 Jul 2019 19:11:53 +0900	[thread overview]
Message-ID: <20190718101123.GB10041@jagdpanzerIV> (raw)
In-Reply-To: <20190716072805.22445-2-pmladek@suse.com>

On (07/16/19 09:28), Petr Mladek wrote:
[..]
> +int printk_bust_lock_safe(void)
> +{
> +	if (!raw_spin_is_locked(&logbuf_lock))
> +		return 0;
> +
> +	if (num_online_cpus() == 1) {
> +		debug_locks_off();
> +		raw_spin_lock_init(&logbuf_lock);
> +		return 0;
> +	}
> +
> +	return -EWOULDBLOCK;
> +}

A side note:

I'd say that we also need to clear console_owner and re-init
console_owner_lock spin_lock, panic CPU can spin forever
otherwise; and I think it would also be reasonable to re-init
console_sem's spin_lock, yet another lock on which panic CPU
can spin forever. (Assuming that one of remote CPUs that we
have NMI killed had owned any of those locks).

Console drivers' locks are mostly OK, as long as drivers check
oops_in_progress in ->write() path and act accordingly, but
printk() has to deal with more than one lock (logbuf_lock)
before it invokes console drivers.

	-ss

  parent reply	other threads:[~2019-07-18 10:12 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-16  7:28 [PATCH 0/2] panic/printk/x86: Prevent some more printk-related deadlocks in panic() Petr Mladek
2019-07-16  7:28 ` [PATCH 1/2] printk/panic: Access the main printk log in panic() only when safe Petr Mladek
2019-07-17  9:56   ` Sergey Senozhatsky
2019-07-18  8:36     ` Petr Mladek
2019-07-18  9:49       ` Sergey Senozhatsky
2019-07-19 12:57         ` Petr Mladek
2019-07-23  3:13           ` Sergey Senozhatsky
2019-07-24 12:27             ` Petr Mladek
2019-07-31  6:08               ` Sergey Senozhatsky
2019-07-31  6:59                 ` Sergey Senozhatsky
2019-07-18 10:11   ` Sergey Senozhatsky [this message]
2019-07-16  7:28 ` [PATCH 2/2] printk/panic/x86: Allow to access printk log buffer after crash_smp_send_stop() Petr Mladek
2019-07-18 10:47   ` Sergey Senozhatsky
2019-07-18 11:07     ` Konstantin Khlebnikov
2019-07-18 11:29       ` Sergey Senozhatsky
2019-07-19 12:19         ` Petr Mladek
2019-07-18  9:59 ` [PATCH 0/2] panic/printk/x86: Prevent some more printk-related deadlocks in panic() Konstantin Khlebnikov

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