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Commit c22ab332 authored by Matthew Garrett's avatar Matthew Garrett Committed by Linus Torvalds
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kmsg_dump: don't run on non-error paths by default 



Since commit 04c6862c ("kmsg_dump: add kmsg_dump() calls to the
reboot, halt, poweroff and emergency_restart paths"), kmsg_dump() gets
run on normal paths including poweroff and reboot.

This is less than ideal given pstore implementations that can only
represent single backtraces, since a reboot may overwrite a stored oops
before it's been picked up by userspace.  In addition, some pstore
backends may have low performance and provide a significant delay in
reboot as a result.

This patch adds a printk.always_kmsg_dump kernel parameter (which can also
be changed from userspace).  Without it, the code will only be run on
failure paths rather than on normal paths.  The option can be enabled in
environments where there's a desire to attempt to audit whether or not a
reboot was cleanly requested or not.

Signed-off-by: default avatarMatthew Garrett <mjg@redhat.com>
Acked-by: default avatarSeiji Aguchi <seiji.aguchi@hds.com>
Cc: Seiji Aguchi <seiji.aguchi@hds.com>
Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Marco Stornelli <marco.stornelli@gmail.com>
Cc: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Don Zickus <dzickus@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 550cf00d

Documentation/kernel-parameters.txt

+6 −0
Original line number Diff line number Diff line
@@ -2211,6 +2211,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted. 


			default: off.



	printk.always_kmsg_dump=

			Trigger kmsg_dump for cases other than kernel oops or

			panics

			Format: <bool>  (1/Y/y=enable, 0/N/n=disable)

			default: disabled



	printk.time=	Show timing data prefixed to each printk message line

			Format: <bool>  (1/Y/y=enable, 0/N/n=disable)

include/linux/kmsg_dump.h

+7 −2
Original line number Diff line number Diff line
@@ -15,13 +15,18 @@ 
#include <linux/errno.h>

#include <linux/list.h>



/*

 * Keep this list arranged in rough order of priority. Anything listed after

 * KMSG_DUMP_OOPS will not be logged by default unless printk.always_kmsg_dump

 * is passed to the kernel.

 */

enum kmsg_dump_reason {

	KMSG_DUMP_OOPS,

	KMSG_DUMP_PANIC,

	KMSG_DUMP_OOPS,

	KMSG_DUMP_EMERG,

	KMSG_DUMP_RESTART,

	KMSG_DUMP_HALT,

	KMSG_DUMP_POWEROFF,

	KMSG_DUMP_EMERG,

};



/**

kernel/printk.c

+6 −0
Original line number Diff line number Diff line
@@ -702,6 +702,9 @@ static bool printk_time = 0; 
#endif

module_param_named(time, printk_time, bool, S_IRUGO | S_IWUSR);



static bool always_kmsg_dump;

module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);



/* Check if we have any console registered that can be called early in boot. */

static int have_callable_console(void)

{
@@ -1732,6 +1735,9 @@ void kmsg_dump(enum kmsg_dump_reason reason) 
	unsigned long l1, l2;

	unsigned long flags;



	if ((reason > KMSG_DUMP_OOPS) && !always_kmsg_dump)

		return;



	/* Theoretically, the log could move on after we do this, but

	   there's not a lot we can do about that. The new messages

	   will overwrite the start of what we dump. */