From: Petr Mladek <pmladek@suse.com>
To: John Ogness <john.ogness@linutronix.de>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
linux-kernel@vger.kernel.org,
"Paul E. McKenney" <paulmck@kernel.org>,
Frederic Weisbecker <frederic@kernel.org>,
Neeraj Upadhyay <quic_neeraju@quicinc.com>,
Joel Fernandes <joel@joelfernandes.org>,
Josh Triplett <josh@joshtriplett.org>,
Boqun Feng <boqun.feng@gmail.com>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Zqiang <qiang.zhang1211@gmail.com>,
rcu@vger.kernel.org
Subject: Re: [PATCH printk v2 25/26] rcu: Mark emergency section in rcu stalls
Date: Fri, 1 Mar 2024 16:13:27 +0100 [thread overview]
Message-ID: <ZeHwl63uXDZ9ZBtt@alley> (raw)
In-Reply-To: <20240218185726.1994771-26-john.ogness@linutronix.de>
On Sun 2024-02-18 20:03:25, John Ogness wrote:
> Mark an emergency section within print_other_cpu_stall(), where
> RCU stall information is printed. In this section, the CPU will
> not perform console output for the printk() calls. Instead, a
> flushing of the console output is triggered when exiting the
> emergency section.
>
> Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Petr Mladek <pmladek@suse.com>
I was just curious about one thing. But it seems to work well.
print_other_cpu_stall() print backtraces on other CPUs via NMI.
The other CPUs would not see the emergency context. They would
call defer_console_output() because they are in NMI. As a result:
+ Legacy consoles might be flushed on other CPUs even before
nbcon_cpu_emergency_exit() gets called.
+ nbcon consoles might still be flushed by the printk kthread
until all messages get flushed directly by nbcon_cpu_emergency_exit()
As I wrote. The behavior is corrent. It was just not obvious to me.
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -9,6 +9,7 @@
>
> #include <linux/kvm_para.h>
> #include <linux/rcu_notifier.h>
> +#include <linux/console.h>
>
> //////////////////////////////////////////////////////////////////////////////
> //
> @@ -604,6 +605,8 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
> if (rcu_stall_is_suppressed())
> return;
>
> + nbcon_cpu_emergency_enter();
> +
> /*
> * OK, time to rat on our buddy...
> * See Documentation/RCU/stallwarn.rst for info on how to debug
> @@ -658,6 +661,8 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps)
> panic_on_rcu_stall();
>
> rcu_force_quiescent_state(); /* Kick them all. */
> +
> + nbcon_cpu_emergency_exit();
> }
>
> static void print_cpu_stall(unsigned long gps)
Best Regards,
Petr
prev parent reply other threads:[~2024-03-01 15:13 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-18 18:57 [PATCH printk v2 00/26] wire up write_atomic() printing John Ogness
2024-02-18 18:57 ` [PATCH printk v2 25/26] rcu: Mark emergency section in rcu stalls John Ogness
2024-03-01 15:13 ` Petr Mladek [this message]
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=ZeHwl63uXDZ9ZBtt@alley \
--to=pmladek@suse.com \
--cc=boqun.feng@gmail.com \
--cc=frederic@kernel.org \
--cc=jiangshanlai@gmail.com \
--cc=joel@joelfernandes.org \
--cc=john.ogness@linutronix.de \
--cc=josh@joshtriplett.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mathieu.desnoyers@efficios.com \
--cc=paulmck@kernel.org \
--cc=qiang.zhang1211@gmail.com \
--cc=quic_neeraju@quicinc.com \
--cc=rcu@vger.kernel.org \
--cc=rostedt@goodmis.org \
--cc=senozhatsky@chromium.org \
--cc=tglx@linutronix.de \
/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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).