Commit 56e6c104 authored Jul 31, 2018 by Thomas Zimmermann Committed by Bartlomiej Zolnierkiewicz Jul 31, 2018

console: Replace #if 0 with atomic var 'ignore_console_lock_warning'

The macro WARN_CONSOLE_UNLOCKED prints a warning when a thread enters
the console's critical section without having acquired the console
lock. The console lock can be ignored when debugging the console using
printk, but this makes WARN_CONSOLE_UNLOCKED generate unnecessary
warnings.

The variable ignore_console_lock_warning temporarily disables
WARN_CONSOLE_UNLOCKED. Developers interested in debugging the console's
critical sections should increment it before entering the CS and
decrement it after leaving the CS. Setting ignore_console_lock_warning
is only for debugging. Regular operation should not manipulate it.

Acknoledgements: This patch is based on an earlier version by Steven
Rostedt. The use of atomic increment/decrement was suggested by Petr
Mladek.

Link: http://lkml.kernel.org/r/717e6337-e7a6-7a92-1c1b-8929a25696b5@suse.de


Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
[b.zolnierkie: use <linux/atomic.h>]
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>

parent cb782a3f

include/linux/console.h

+9 −5

Original line number	Diff line number	Diff line
		@@ -14,6 +14,7 @@
		#ifndef _LINUX_CONSOLE_H_
		#define _LINUX_CONSOLE_H_ 1

		#include <linux/atomic.h>
		#include <linux/types.h>

		struct vc_data;
		@@ -201,11 +202,14 @@ void vcs_make_sysfs(int index);
		void vcs_remove_sysfs(int index);

		/* Some debug stub to catch some of the obvious races in the VT code */
		#if 1
		#define WARN_CONSOLE_UNLOCKED() WARN_ON(!is_console_locked() && !oops_in_progress)
		#else
		#define WARN_CONSOLE_UNLOCKED()
		#endif
		#define WARN_CONSOLE_UNLOCKED() \
		WARN_ON(!atomic_read(&ignore_console_lock_warning) && \
		!is_console_locked() && !oops_in_progress)
		/*
		* Increment ignore_console_lock_warning if you need to quiet
		* WARN_CONSOLE_UNLOCKED() for debugging purposes.
		*/
		extern atomic_t ignore_console_lock_warning;

		/* VESA Blanking Levels */
		#define VESA_NO_BLANKING 0

kernel/printk/printk.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -66,6 +66,9 @@ int console_printk[4] = {
		CONSOLE_LOGLEVEL_DEFAULT, /* default_console_loglevel */
		};

		atomic_t ignore_console_lock_warning __read_mostly = ATOMIC_INIT(0);
		EXPORT_SYMBOL(ignore_console_lock_warning);

		/*
		* Low level drivers may need that to know if they can schedule in
		* their unblank() callback or not. So let's export it.

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