From: John Ogness <john.ogness@linutronix.de>
To: Petr Mladek <pmladek@suse.com>, Douglas Anderson <dianders@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Li Zhe <lizhe.67@bytedance.com>,
Pingfan Liu <kernelfans@gmail.com>,
Lecopzer Chen <lecopzer.chen@mediatek.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/4] watchdog: Better handling of concurrent lockups
Date: Tue, 06 Feb 2024 11:51:50 +0106 [thread overview]
Message-ID: <87ttmlan1d.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <ZcIGKU8sxti38Kok@alley>
On 2024-02-06, Petr Mladek <pmladek@suse.com> wrote:
> I have just got an idea how to make printk_cpu_sync_get_irqsave()
> less error prone for deadlock on the panic() CPU. The idea is
> to ignore the lock or give up locking after a timeout on
> the panic CPU.
This idea is out of scope for this series. But it is something we should
think about. The issue has always been a possible problem in panic().
> AFAIK, the lock is currently used only to serialize related
> printk() calls. The only risk is that some messages might be
> interleaved when it is ignored.
>
> I am not sure if this is a good idea though. It might create
> another risk when the lock gets used to serialize more
> things in the future and a race might create a real problem.
With the printk series we are currently working on [0], only the panic
CPU can store new printk messages anyway. So there would be nothing to
synchronize against (and it could be safely ignored).
kgdb uses the same technique to quiesce the CPUs. It does not use the
printk_cpu_sync for this, but it is an example of a possible future
usage not related to printk.
My vote is to make it a NOP for the panic CPU and then keep an eye on
any future uses. Should I add this to v4 of [0]?
John
[0] https://lore.kernel.org/lkml/20231214214201.499426-1-john.ogness@linutronix.de
next prev parent reply other threads:[~2024-02-06 10:46 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-20 21:15 [PATCH 0/4] watchdog: Better handling of concurrent lockups Douglas Anderson
2023-12-20 21:15 ` [PATCH 1/4] watchdog/hardlockup: Adopt softlockup logic avoiding double-dumps Douglas Anderson
2023-12-20 21:15 ` [PATCH 2/4] watchdog/softlockup: Use printk_cpu_sync_get_irqsave() to serialize reporting Douglas Anderson
2023-12-22 7:13 ` lizhe.67
2023-12-22 9:30 ` John Ogness
2024-02-06 10:21 ` Petr Mladek
2023-12-20 21:15 ` [PATCH 3/4] watchdog/hardlockup: " Douglas Anderson
2023-12-22 9:42 ` John Ogness
2023-12-20 21:15 ` [PATCH 4/4] watchdog: If panicking and we dumped everything, don't re-enable dumping Douglas Anderson
2024-02-06 10:12 ` [PATCH 0/4] watchdog: Better handling of concurrent lockups Petr Mladek
2024-02-06 10:45 ` John Ogness [this message]
2024-02-06 19:31 ` Doug Anderson
2024-02-07 13:04 ` Petr Mladek
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87ttmlan1d.fsf@jogness.linutronix.de \
--to=john.ogness@linutronix.de \
--cc=akpm@linux-foundation.org \
--cc=dianders@chromium.org \
--cc=kernelfans@gmail.com \
--cc=lecopzer.chen@mediatek.com \
--cc=linux-kernel@vger.kernel.org \
--cc=lizhe.67@bytedance.com \
--cc=pmladek@suse.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.