From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: Petr Mladek <pmladek@suse.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH printk 4/5] printk: remove logbuf_lock, add syslog_lock
Date: Thu, 24 Sep 2020 17:45:41 +0900 [thread overview]
Message-ID: <20200924084541.GA541@jagdpanzerIV.localdomain> (raw)
In-Reply-To: <20200922153816.5883-5-john.ogness@linutronix.de>
On (20/09/22 17:44), John Ogness wrote:
[..]
> void printk_safe_flush_on_panic(void)
> {
> - /*
> - * Make sure that we could access the main ring buffer.
> - * Do not risk a double release when more CPUs are up.
> - */
> - if (raw_spin_is_locked(&logbuf_lock)) {
> - if (num_online_cpus() > 1)
> - return;
> -
> - debug_locks_off();
> - raw_spin_lock_init(&logbuf_lock);
If we panic() with syslog_lock locked then we need to zap syslog_lock
and disable debug_locks for kmsg_dump() to succeed. Otherwise panic()
may deadlock:
syslog_lock_irq()
-> NMI
panic()
...
printk_safe_flush_on_panic();
kmsg_dump(KMSG_DUMP_PANIC); // syslog_lock_irqsave(flags)
...
Did I miss the point where we make sure that kmsg_dump() will not
deadlock?
-ss
next prev parent reply other threads:[~2020-09-24 8:45 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-22 15:38 [PATCH printk 0/5] printk: remove logbuf_lock John Ogness
2020-09-22 15:38 ` [PATCH printk 1/5] printk: get new seq before enabling interrupts John Ogness
2020-09-23 14:17 ` Petr Mladek
2020-09-23 14:36 ` John Ogness
2020-09-22 15:38 ` [PATCH printk 2/5] printk: kmsg_dump_rewind_nolock: start from first record John Ogness
2020-09-23 14:52 ` Petr Mladek
2020-09-23 15:39 ` John Ogness
2020-09-22 15:38 ` [PATCH printk 3/5] printk: use buffer pool for sprint buffers John Ogness
2020-09-23 15:11 ` Petr Mladek
2020-09-23 15:21 ` David Laight
2020-09-23 16:41 ` Petr Mladek
2020-09-24 5:40 ` Sergey Senozhatsky
2020-09-24 8:45 ` Petr Mladek
2020-09-24 8:53 ` Sergey Senozhatsky
2020-09-24 9:49 ` Rasmus Villemoes
2020-09-25 8:15 ` Petr Mladek
2020-09-24 9:54 ` Rasmus Villemoes
2020-09-24 12:32 ` Rasmus Villemoes
2020-09-25 8:28 ` Petr Mladek
2020-09-30 8:06 ` Rasmus Villemoes
2020-09-30 8:51 ` Petr Mladek
2020-09-30 8:57 ` John Ogness
2020-09-30 13:35 ` Steven Rostedt
2020-09-30 14:32 ` David Laight
2020-10-01 7:15 ` Rasmus Villemoes
2020-10-01 7:58 ` Petr Mladek
2020-09-24 1:21 ` Sergey Senozhatsky
2020-09-24 6:17 ` Sergey Senozhatsky
2020-09-24 8:54 ` Petr Mladek
2020-09-24 9:06 ` Sergey Senozhatsky
2020-09-25 8:13 ` Petr Mladek
2020-09-22 15:38 ` [PATCH printk 4/5] printk: remove logbuf_lock, add syslog_lock John Ogness
2020-09-23 16:30 ` Petr Mladek
2020-09-24 8:45 ` Sergey Senozhatsky [this message]
2020-09-24 9:21 ` John Ogness
2020-09-22 15:38 ` [PATCH printk 5/5] printk: remove nmi safe buffers John Ogness
2020-09-23 16:36 ` Petr Mladek
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