From: Petr Mladek <pmladek@suse.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
Steven Rostedt <rostedt@goodmis.org>,
Daniel Wang <wonderfly@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
Jiri Slaby <jslaby@suse.com>, Peter Feiner <pfeiner@google.com>,
linux-serial@vger.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: [RFC PATCH v1 11/25] printk_safe: remove printk safe code
Date: Fri, 22 Feb 2019 16:15:24 +0100 [thread overview]
Message-ID: <20190222151524.2iosxbcpn5bb4cbq@pathway.suse.cz> (raw)
In-Reply-To: <87h8cwymcr.fsf@linutronix.de>
On Fri 2019-02-22 14:38:28, John Ogness wrote:
> On 2019-02-22, Petr Mladek <pmladek@suse.com> wrote:
> >> diff --git a/lib/nmi_backtrace.c b/lib/nmi_backtrace.c
> >> index 15ca78e1c7d4..77bf84987cda 100644
> >> --- a/lib/nmi_backtrace.c
> >> +++ b/lib/nmi_backtrace.c
> >> @@ -75,12 +75,6 @@ void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
> >> touch_softlockup_watchdog();
> >> }
> >>
> >> - /*
> >> - * Force flush any remote buffers that might be stuck in IRQ context
> >> - * and therefore could not run their irq_work.
> >> - */
> >> - printk_safe_flush();
> >> -
> >> clear_bit_unlock(0, &backtrace_flag);
> >> put_cpu();
> >> }
> >
> > This reminds me that we need to add back the locking that was
> > removed in the commit 03fc7f9c99c1e7ae2925d45 ("printk/nmi:
> > Prevent deadlock when accessing the main log buffer in NMI").
>
> No, that commit is needed. You cannot have NMIs waiting on other CPUs.
It sounds weird. But it is safe to use a lock when it is used only
in the NMI context.
The lock has always been there. For example, I found it in
the commit 1fb9d6ad2766a1dd70 ("nmi_watchdog: Add new,
generic implementation, using perf events") from v2.6.36.
It could get removed only because we switched to the per-CPU
buffers.
> > Otherwise, backtraces from different CPUs would get mixed.
>
> A later patch (#17) adds CPU IDs to the printk messages so that this
> isn't a problem. (That patch is actually obsolete now because Sergey has
> already merged work for linux-next that includes this information.)
No this is not enough. First, the CPU-ids were primary added for
kernel testers (0-day robot, kernel-ci, syzcaller). It is not
enabled by default. It is not handled by kmsg interface.
Also sorting the messages is not much user friendly.
It should be the last resort when no other solution
is possible.
Best Regards,
Petr
next prev parent reply other threads:[~2019-02-22 15:15 UTC|newest]
Thread overview: 147+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-12 14:29 [RFC PATCH v1 00/25] printk: new implementation John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 01/25] printk-rb: add printk ring buffer documentation John Ogness
2019-02-12 14:45 ` Greg Kroah-Hartman
2019-02-12 14:29 ` [RFC PATCH v1 02/25] printk-rb: add prb locking functions John Ogness
2019-02-13 15:45 ` Petr Mladek
2019-02-13 21:39 ` John Ogness
2019-02-14 10:33 ` Petr Mladek
2019-02-14 12:10 ` John Ogness
2019-02-15 10:26 ` Petr Mladek
2019-02-15 10:56 ` John Ogness
2019-03-07 2:12 ` Sergey Senozhatsky
2019-02-12 14:29 ` [RFC PATCH v1 03/25] printk-rb: define ring buffer struct and initializer John Ogness
2019-02-12 14:46 ` Greg Kroah-Hartman
2019-02-14 12:46 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 04/25] printk-rb: add writer interface John Ogness
2019-02-14 15:16 ` Petr Mladek
2019-02-14 23:36 ` John Ogness
2019-02-15 1:19 ` John Ogness
2019-02-15 13:47 ` Petr Mladek
2019-02-17 1:32 ` John Ogness
2019-02-21 13:51 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 05/25] printk-rb: add basic non-blocking reading interface John Ogness
2019-02-18 12:54 ` Petr Mladek
2019-02-19 21:44 ` John Ogness
2019-02-21 16:22 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 06/25] printk-rb: add blocking reader support John Ogness
2019-02-18 14:05 ` Petr Mladek
2019-02-19 21:47 ` John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 07/25] printk-rb: add functionality required by printk John Ogness
2019-02-12 17:15 ` Linus Torvalds
2019-02-13 9:20 ` John Ogness
2019-02-18 15:59 ` Petr Mladek
2019-02-19 22:08 ` John Ogness
2019-02-22 9:58 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 08/25] printk: add ring buffer and kthread John Ogness
2019-02-12 15:47 ` Sergey Senozhatsky
2019-02-19 13:54 ` Petr Mladek
2019-03-04 7:38 ` Sergey Senozhatsky
2019-03-04 10:00 ` Sergey Senozhatsky
2019-03-04 11:07 ` Sergey Senozhatsky
2019-03-05 21:00 ` John Ogness
2019-03-06 15:57 ` Petr Mladek
2019-03-06 21:17 ` John Ogness
2019-03-06 22:22 ` John Ogness
2019-03-07 6:41 ` Sergey Senozhatsky
2019-03-07 6:51 ` Sergey Senozhatsky
2019-03-07 12:50 ` Petr Mladek
2019-03-07 5:15 ` Sergey Senozhatsky
2019-03-11 10:51 ` John Ogness
2019-03-12 9:58 ` Sergey Senozhatsky
2019-03-12 10:30 ` Petr Mladek
2019-03-07 12:06 ` John Ogness
2019-03-08 1:31 ` Sergey Senozhatsky
2019-03-08 10:04 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 09/25] printk: remove exclusive console hack John Ogness
2019-02-19 14:03 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 10/25] printk: redirect emit/store to new ringbuffer John Ogness
2019-02-20 9:01 ` Petr Mladek
2019-02-20 21:25 ` John Ogness
2019-02-22 14:43 ` Petr Mladek
2019-02-22 15:06 ` John Ogness
2019-02-22 15:25 ` Petr Mladek
2019-02-25 12:11 ` Petr Mladek
2019-02-25 16:41 ` John Ogness
2019-02-26 9:45 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 11/25] printk_safe: remove printk safe code John Ogness
2019-02-22 10:37 ` Petr Mladek
2019-02-22 13:38 ` John Ogness
2019-02-22 15:15 ` Petr Mladek [this message]
2019-02-12 14:29 ` [RFC PATCH v1 12/25] printk: minimize console locking implementation John Ogness
2019-02-25 13:44 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 13/25] printk: track seq per console John Ogness
2019-02-25 14:59 ` Petr Mladek
2019-02-26 8:45 ` John Ogness
2019-02-26 13:11 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 14/25] printk: do boot_delay_msec inside printk_delay John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 15/25] printk: print history for new consoles John Ogness
2019-02-26 14:58 ` Petr Mladek
2019-02-26 15:22 ` John Ogness
2019-02-27 9:02 ` Petr Mladek
2019-02-27 10:02 ` John Ogness
2019-02-27 13:12 ` Petr Mladek
2019-03-04 9:24 ` Sergey Senozhatsky
2019-02-12 14:29 ` [RFC PATCH v1 16/25] printk: implement CON_PRINTBUFFER John Ogness
2019-02-26 15:38 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 17/25] printk: add processor number to output John Ogness
2019-02-13 22:29 ` John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 18/25] console: add write_atomic interface John Ogness
2019-02-12 14:29 ` [RFC PATCH v1 19/25] printk: introduce emergency messages John Ogness
2019-03-07 7:30 ` Sergey Senozhatsky
2019-03-08 10:31 ` Petr Mladek
2019-03-11 12:04 ` John Ogness
2019-03-12 2:51 ` Sergey Senozhatsky
2019-03-12 2:58 ` Sergey Senozhatsky
2019-02-12 14:29 ` [RFC PATCH v1 20/25] serial: 8250: implement write_atomic John Ogness
2019-02-27 9:46 ` Petr Mladek
2019-02-27 10:32 ` John Ogness
2019-02-27 13:55 ` Petr Mladek
2019-03-08 4:05 ` John Ogness
2019-03-08 4:17 ` John Ogness
2019-03-08 10:28 ` Petr Mladek
2019-02-12 14:29 ` [RFC PATCH v1 21/25] printk: implement KERN_CONT John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 22/25] printk: implement /dev/kmsg John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 23/25] printk: implement syslog John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 24/25] printk: implement kmsg_dump John Ogness
2019-02-12 14:30 ` [RFC PATCH v1 25/25] printk: remove unused code John Ogness
2019-03-08 14:02 ` Sebastian Andrzej Siewior
2019-03-11 2:46 ` Sergey Senozhatsky
2019-03-11 8:18 ` Sebastian Andrzej Siewior
2019-03-12 9:38 ` Petr Mladek
2019-02-13 1:31 ` [RFC PATCH v1 00/25] printk: new implementation Sergey Senozhatsky
2019-02-13 13:43 ` John Ogness
2019-03-04 6:39 ` Sergey Senozhatsky
2019-02-13 1:41 ` Sergey Senozhatsky
2019-02-13 14:15 ` John Ogness
2019-03-04 5:31 ` Sergey Senozhatsky
2019-02-13 2:55 ` Sergey Senozhatsky
2019-02-13 14:43 ` John Ogness
2019-03-04 5:23 ` Sergey Senozhatsky
2019-03-07 9:53 ` John Ogness
2019-03-08 10:00 ` Petr Mladek
2019-03-11 10:54 ` Sergey Senozhatsky
2019-03-12 12:38 ` Petr Mladek
2019-03-12 15:15 ` John Ogness
2019-03-13 2:15 ` Sergey Senozhatsky
2019-03-13 8:19 ` John Ogness
2019-03-13 8:40 ` Sebastian Siewior
2019-03-13 9:27 ` Sergey Senozhatsky
2019-03-13 10:06 ` Sergey Senozhatsky
2019-03-14 9:27 ` Petr Mladek
2019-03-13 8:46 ` Sergey Senozhatsky
2019-03-14 9:14 ` Petr Mladek
2019-03-14 9:35 ` John Ogness
2019-03-13 2:00 ` Sergey Senozhatsky
2019-02-13 16:54 ` David Laight
2019-02-13 22:20 ` John Ogness
2020-01-20 23:05 ` Eugeniu Rosca
2020-01-21 23:56 ` John Ogness
2020-01-22 2:34 ` Eugeniu Rosca
2020-01-22 7:31 ` Geert Uytterhoeven
2020-01-22 16:58 ` Eugeniu Rosca
2020-01-22 19:48 ` Geert Uytterhoeven
2020-01-24 16:09 ` Eugeniu Rosca
2020-01-27 12:32 ` Petr Mladek
2020-01-27 13:45 ` Eugeniu Rosca
2020-01-22 10:33 ` John Ogness
2020-01-24 12:13 ` Eugeniu Rosca
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