public inbox for [email protected]
 help / color / mirror / Atom feed
From: "Paul E. McKenney" <[email protected]>
To: John Ogness <[email protected]>
Cc: [email protected], [email protected],
	[email protected], [email protected], Petr Mladek <[email protected]>,
	Sergey Senozhatsky <[email protected]>,
	Steven Rostedt <[email protected]>
Subject: Re: [PATCH rcu 1/2] torture: Optionally flush printk() buffers before powering off
Date: Thu, 1 Sep 2022 03:17:40 -0700	[thread overview]
Message-ID: <20220901101740.GP6159@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <[email protected]>

On Thu, Sep 01, 2022 at 11:18:20AM +0206, John Ogness wrote:
> Added CC the rest of the printk folks since this would be the first use
> of pr_flush() outside of the printk subsystem. And it is a controversial
> usage, since it is used to work around potential (future) bugs in
> printk.
> 
> On 2022-08-31, "Paul E. McKenney" <[email protected]> wrote:
> > The rcutorture test suite produces quite a bit of console output at
> > the end of a test.  This means that the new-in-2022 printk() kthreads
> > are likely to be in the process of flushing output at the time of the
> > torture_shutdown() function's call to kernel_power_off().  Normally,
> > rcutorture relies on printk() to flush any pending output upon shutdown,
> > the better to detect bugs in this area, for example, the one introduced
> > by 8e274732115f ("printk: extend console_lock for per-console locking").
> > However, once such a bug is detected and reported, it is necessary to
> > test the rest of the system, without noise from the already-reported bug.
> 
> Since the printk kthread implementation has been reverted, this is no
> longer an issue. When a kthread implementation is re-introduced, this
> issue will need to have been considered and handled.
> 
> IMHO this patch is premature at this time and hopefully will never
> become necessary (in the form of a bug workaround).

Very well, I will drop it, for the time being, anyway.  ;-)

							Thanx, Paul

> > This commit therefore adds a torture.printk_shutdown_bug_workaround
> > kernel parameter, which causes torture_shutdown() to invoke pr_flush(),
> > and print an informative message on the console, immediately before
> > invoking kernel_power_off().  When this kernel parameter is not specified,
> > it is up to printk() to flush its own buffers.
> >
> > Suggested-by: John Ogness <[email protected]>
> > Signed-off-by: Paul E. McKenney <[email protected]>
> > ---
> >  Documentation/admin-guide/kernel-parameters.txt | 6 ++++++
> >  kernel/torture.c                                | 7 +++++++
> >  2 files changed, 13 insertions(+)
> >
> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index d7f30902fda02..ba1b8776aab83 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -6143,6 +6143,12 @@
> >  			are running concurrently, especially on systems
> >  			with rotating-rust storage.
> >  
> > +	torture.printk_shutdown_bug_workaround= [KNL]
> > +			Execute pr_flush(1000, true) just before invoking
> > +			kernel_power_off() to work around any bugs that
> > +			might prevent printk() from flushing its buffers
> > +			at shutdown time.
> > +
> >  	torture.verbose_sleep_frequency= [KNL]
> >  			Specifies how many verbose printk()s should be
> >  			emitted between each sleep.  The default of zero
> > diff --git a/kernel/torture.c b/kernel/torture.c
> > index 789aeb0e1159c..7cd2016b02076 100644
> > --- a/kernel/torture.c
> > +++ b/kernel/torture.c
> > @@ -48,6 +48,9 @@ module_param(disable_onoff_at_boot, bool, 0444);
> >  static bool ftrace_dump_at_shutdown;
> >  module_param(ftrace_dump_at_shutdown, bool, 0444);
> >  
> > +static bool printk_shutdown_bug_workaround;
> > +module_param(printk_shutdown_bug_workaround, bool, 0444);
> > +
> >  static int verbose_sleep_frequency;
> >  module_param(verbose_sleep_frequency, int, 0444);
> >  
> > @@ -651,6 +654,10 @@ static int torture_shutdown(void *arg)
> >  		VERBOSE_TOROUT_STRING("No torture_shutdown_hook(), skipping.");
> >  	if (ftrace_dump_at_shutdown)
> >  		rcu_ftrace_dump(DUMP_ALL);
> > +	if (printk_shutdown_bug_workaround) {
> > +		pr_info("%s: Flushing printk() buffers at power-down time.\n", __func__);
> > +		pr_flush(1000, true);
> > +	}
> >  	kernel_power_off();	/* Shut down the system. */
> >  	return 0;
> >  }
> > -- 
> > 2.31.1.189.g2e36527f23
> 
> John Ogness

  reply	other threads:[~2022-09-01 10:17 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-31 18:21 [PATCH nolibc 0/18] nolibc updates for v6.1 Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 01/18] tools/nolibc: make argc 32-bit in riscv startup code Paul E. McKenney
2022-08-31 18:21 ` [PATCH rcu 1/2] torture: Optionally flush printk() buffers before powering off Paul E. McKenney
2022-09-01  9:12   ` John Ogness
2022-09-01 10:17     ` Paul E. McKenney [this message]
2022-08-31 18:21 ` [PATCH rcu 2/2] rcutorture: Use the barrier operation specified by cur_ops Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 02/18] tools/nolibc: fix build warning in sys_mmap() when my_syscall6 is not defined Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 03/18] tools/nolibc: make sys_mmap() automatically use the right __NR_mmap definition Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 04/18] selftests/nolibc: add basic infrastructure to ease creation of nolibc tests Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 05/18] selftests/nolibc: support a test definition format Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 06/18] selftests/nolibc: implement a few tests for various syscalls Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 07/18] selftests/nolibc: add a few tests for some libc functions Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 08/18] selftests/nolibc: exit with poweroff on success when getpid() == 1 Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 09/18] selftests/nolibc: on x86, support exiting with isa-debug-exit Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 10/18] selftests/nolibc: recreate and populate /dev and /proc if missing Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 11/18] selftests/nolibc: condition some tests on /proc existence Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 12/18] selftests/nolibc: support glibc as well Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 13/18] selftests/nolibc: add a "kernel" target to build the kernel with the initramfs Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 14/18] selftests/nolibc: add a "defconfig" target Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 15/18] selftests/nolibc: add a "run" target to start the kernel in QEMU Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 16/18] selftests/nolibc: "sysroot" target installs a local copy of the sysroot Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 17/18] selftests/nolibc: add a "help" target Paul E. McKenney
2022-08-31 18:21 ` [PATCH nolibc 18/18] selftests/nolibc: Avoid generated files being committed Paul E. McKenney

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=20220901101740.GP6159@paulmck-ThinkPad-P17-Gen-1 \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    [email protected] \
    /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