kmsg_dump: don't run on non-error paths by default (c22ab332) · Commits · 戴 / test

Since commit ("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:

Matthew Garrett <mjg@redhat.com> Acked-by:

Seiji 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:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

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. */

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