From: Konstantin Khlebnikov <koct9i@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>,
x86@kernel.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 0/2] panic/printk/x86: Prevent some more printk-related deadlocks in panic()
Date: Thu, 18 Jul 2019 12:59:47 +0300 [thread overview]
Message-ID: <CALYGNiPETLPeOOuRwQtYca=yrwWHgg11A6Fc_qZipG56N8KP8A@mail.gmail.com> (raw)
In-Reply-To: <20190716072805.22445-1-pmladek@suse.com>
On Tue, Jul 16, 2019 at 10:28 AM Petr Mladek <pmladek@suse.com> wrote:
>
> Hi,
>
> I have found some spare duct tape and wrapped some more printk-related
> deadlocks in panic().
>
> More seriously, someone reported a deadlock in panic(). Some non-trivial
> debugging pointed out a problem with the following combination:
>
> + x86_64 architecture
> + panic()
> + pstore configured as message dumper (kmsg_dump())
> + crash kernel configured
> + crash_kexec_post_notifiers
>
> In this case, CPUs are stopped by crash_smp_send_stop(). It uses
> NMI but it does not modify cpu_online_mask. Therefore logbuf_lock
> might stay locked, see 2nd patch for more details.
>
> The above is a real corner case. But similar problem seems to be
> even in the common situations on architectures that do not use
> NMI in smp_send_stop() as a fallback, see 1st patch.
>
> Back to the duct tape. I hope that we will get rid of these problems
> with the lockless printk ringbuffer rather sooner than later.
> But it still might take some time. And the two fixes might be
> useful also for stable kernels.
Looks good.
Reviewed-by: Konstantin Khebnikov <khlebnikov@yandex-team.ru>
>
>
> Petr Mladek (2):
> printk/panic: Access the main printk log in panic() only when safe
> printk/panic/x86: Allow to access printk log buffer after
> crash_smp_send_stop()
>
> arch/x86/kernel/crash.c | 6 +++++-
> include/linux/printk.h | 6 ++++++
> kernel/panic.c | 49 +++++++++++++++++++++++++++------------------
> kernel/printk/printk_safe.c | 37 ++++++++++++++++++++++------------
> 4 files changed, 65 insertions(+), 33 deletions(-)
>
> --
> 2.16.4
>
prev parent reply other threads:[~2019-07-18 10:00 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
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 ` Konstantin Khlebnikov [this message]
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