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kmsg_dump: don't run on non-error paths by default

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Since commit 04c6862c05 ("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 <[email protected]>
Acked-by: Seiji Aguchi <[email protected]>
Cc: Seiji Aguchi <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: Marco Stornelli <[email protected]>
Cc: Artem Bityutskiy <[email protected]>
Cc: KOSAKI Motohiro <[email protected]>
Cc: Vivek Goyal <[email protected]>
Cc: Don Zickus <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Matthew Garrett 2012-03-05 14:59:10 -08:00 • committed by Linus Torvalds
commit c22ab33290
3 changed files with 19 additions and 2 deletions
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6
kernel/printk.c
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@ -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. */