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,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH printk v1 03/13] printk: use percpu flag instead of cpu_online()
Date: Fri, 4 Mar 2022 16:56:55 +0100 [thread overview]
Message-ID: <YiI2x6K5IhsADEmK@alley> (raw)
In-Reply-To: <87zgm8h1tt.fsf@jogness.linutronix.de>
On Wed 2022-03-02 15:27:50, John Ogness wrote:
> I have taken some time to investigate the percpu implementation so that
> I could provide clear answers here.
>
> On 2022-02-15, Petr Mladek <pmladek@suse.com> wrote:
> > I am not 100% sure. But it seems that static per-CPU variables might
> > actually be used since the boot.
>
> You are correct, but until per-cpu areas are setup, they all point to
> CPU0. Normally that is not a problem since usually code is using
> this_cpu_ptr() (which will always be the CPU0 in early boot), rather
> than specifying foreign CPUs with per_cpu_ptr().
>
> > Most likely, only dynamically allocated per-cpu variables have to wait
> > until the per-cpu areas are initialized.
>
> It is also important to wait if data will be stored that is no longer
> valid after per-cpu areas are setup. setup_per_cpu_areas() copies the
> static CPU0 per-cpu value to all the newly setup per-cpu areas.
>
> This is actually the cause for the mystery [0] of failing irq_work when
> printk_deferred was added with commit
> 15341b1dd409749fa5625e4b632013b6ba81609b ("char/random: silence a
> lockdep splat with printk()".
Just for record, the right commit ID in the mainline is
1b710b1b10eff9d466. It used printk_deferred() in _warn_unseeded_randomness():
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1687,8 +1687,9 @@ static void _warn_unseeded_randomness(const char *func_name, void *caller,
print_once = true;
#endif
if (__ratelimit(&unseeded_warning))
- pr_notice("random: %s called from %pS with crng_init=%d\n",
- func_name, caller, crng_init);
+ printk_deferred(KERN_NOTICE "random: %s called from %pS "
+ "with crng_init=%d\n", func_name, caller,
+ crng_init);
}
/*
> By avoiding queueing irq_work before setup_per_cpu_areas(), we correctly
> avoided this problem. (I considered sending a patch so that
> irq_work_claim() will fail if a global @percpu_complete is not yet
> set.
That is a great TODO :-)
> But for now, our set_percpu_data_ready() solution is at least good
> enough for the printk subsystem.)
Yes but it is most likely not needed for CON_ANYTIME consoles,
see below.
> > We should probably revisit the code and remove the fallback to
> > normal static variables.
>
> Definitely. Now it is clear that @printk_count and @printk_count_nmi do
> not need early variants.
Note the ordering:
asmlinkage __visible void __init __no_sanitize_address start_kernel(void)
{
[...]
early_security_init();
[...]
setup_per_cpu_areas();
[...]
parse_early_param();
after_dashes = parse_args("Booting kernel",
My guess is that _warn_unseeded_randomness() was called from a code
before early_security_init(). It was bad because per-CPU variables
were not ready yet.
The early consoles are enabled by parse_early_param(). It happens
after setup_per_cpu_areas(). It means that all console drivers
should be on the safe side.
Best Regards,
Petr
next prev parent reply other threads:[~2022-03-04 15:57 UTC|newest]
Thread overview: 87+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-07 19:43 [PATCH printk v1 00/13] implement threaded console printing John Ogness
2022-02-07 19:43 ` [PATCH printk v1 01/13] printk: rename cpulock functions John Ogness
2022-02-11 12:44 ` Petr Mladek
2022-02-11 14:42 ` John Ogness
2022-02-11 20:57 ` Steven Rostedt
2022-02-11 21:04 ` Peter Zijlstra
2022-02-15 9:32 ` Petr Mladek
2022-02-15 9:13 ` Petr Mladek
2022-02-14 6:49 ` Sergey Senozhatsky
2022-02-14 9:45 ` John Ogness
2022-02-15 9:29 ` Petr Mladek
2022-02-16 3:27 ` Sergey Senozhatsky
2022-02-17 14:34 ` John Ogness
2022-02-07 19:43 ` [PATCH printk v1 02/13] printk: cpu sync always disable interrupts John Ogness
2022-02-11 12:58 ` Petr Mladek
2022-02-14 6:36 ` Sergey Senozhatsky
2022-02-07 19:43 ` [PATCH printk v1 03/13] printk: use percpu flag instead of cpu_online() John Ogness
2022-02-11 16:05 ` Petr Mladek
2022-02-14 7:08 ` Sergey Senozhatsky
2022-02-14 7:35 ` Sergey Senozhatsky
2022-02-15 10:38 ` Petr Mladek
2022-02-16 3:29 ` Sergey Senozhatsky
2022-03-02 14:21 ` John Ogness
2022-03-04 15:56 ` Petr Mladek [this message]
2022-03-05 17:05 ` Jason A. Donenfeld
2022-03-07 16:14 ` Petr Mladek
2022-02-16 13:58 ` two locations: was: " Petr Mladek
2022-03-02 14:49 ` John Ogness
2022-03-04 16:14 ` Petr Mladek
2022-03-07 10:06 ` John Ogness
2022-03-08 16:08 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 04/13] printk: get caller_id/timestamp after migration disable John Ogness
2022-02-15 5:53 ` Sergey Senozhatsky
2022-02-15 11:56 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 05/13] printk: call boot_delay_msec() in printk_delay() John Ogness
2022-02-15 5:58 ` Sergey Senozhatsky
2022-02-15 14:59 ` Petr Mladek
2022-02-16 3:21 ` Sergey Senozhatsky
2022-02-15 15:03 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 06/13] printk: refactor and rework printing logic John Ogness
2022-02-16 15:43 ` Petr Mladek
2022-03-02 16:10 ` John Ogness
2022-02-07 19:43 ` [PATCH printk v1 07/13] printk: move buffer definitions into console_emit_next_record() caller John Ogness
2022-02-16 16:10 ` Petr Mladek
2022-03-02 16:25 ` John Ogness
2022-02-07 19:43 ` [PATCH printk v1 08/13] printk: add pr_flush() John Ogness
2022-02-17 10:11 ` Petr Mladek
2022-03-02 17:23 ` John Ogness
2022-03-04 13:24 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 09/13] printk: add functions to allow direct printing John Ogness
2022-02-17 12:52 ` Petr Mladek
2022-02-18 9:00 ` David Laight
2022-02-18 12:52 ` Petr Mladek
2022-03-03 14:37 ` John Ogness
2022-02-07 19:43 ` [PATCH printk v1 10/13] printk: add kthread console printers John Ogness
2022-02-18 9:00 ` early start: was: " Petr Mladek
2022-02-18 9:04 ` start&stop: " Petr Mladek
2022-02-18 9:08 ` main loop: " Petr Mladek
2022-02-18 9:12 ` wake_up_all: " Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 11/13] printk: reimplement console_lock for proper kthread support John Ogness
2022-02-18 16:20 ` Petr Mladek
2022-02-18 21:41 ` John Ogness
2022-02-18 22:03 ` John Ogness
2022-02-22 11:42 ` Petr Mladek
2022-02-23 17:20 ` John Ogness
2022-02-24 8:27 ` Petr Mladek
2022-02-23 10:19 ` Petr Mladek
2022-03-09 13:56 ` John Ogness
2022-03-10 14:34 ` Petr Mladek
2022-03-10 16:08 ` John Ogness
2022-03-11 10:26 ` Petr Mladek
2022-03-11 13:28 ` John Ogness
2022-03-11 16:17 ` Petr Mladek
2022-03-11 22:21 ` John Ogness
2022-03-14 14:08 ` Petr Mladek
2022-03-14 14:43 ` John Ogness
2022-03-14 15:53 ` Petr Mladek
2022-03-11 18:41 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 12/13] printk: remove @console_locked John Ogness
2022-02-23 12:17 ` Petr Mladek
2022-02-07 19:43 ` [PATCH printk v1 13/13] console: introduce CON_MIGHT_SLEEP for vt John Ogness
2022-02-23 13:37 ` Petr Mladek
2022-02-23 18:31 ` Greg Kroah-Hartman
[not found] ` <20220208083620.2736-1-hdanton@sina.com>
2022-02-08 11:08 ` [PATCH printk v1 10/13] printk: add kthread console printers John Ogness
2022-02-08 14:53 ` Petr Mladek
2022-02-14 6:12 ` Sergey Senozhatsky
2022-02-14 10:02 ` Petr Mladek
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