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

Since commit 04c6862c055f ("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>

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 033d4e69b43b107d9780ec959105823e6cefd07c..d99fd9c0ec0e16900663e1378eac9911d4afc845 100644 (file)
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -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)
 

diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index fee66317e071547a4a75e0b90b61399b97249ed2..35f7237ec972bef4ce1ba24cd617571a193ce806 100644 (file)
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -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,
 };
 
 /**

diff --git a/kernel/printk.c b/kernel/printk.c
index 13c0a1143f49438f7cc97718e61ecf5bc5b23747..32690a0b7a1838e1bd9b8bcf8473654955807dae 100644 (file)
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -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. */