panic: add TAINT_SOFTLOCKUP

This taint flag will be set if the system has ever entered a softlockup
state.  Similar to TAINT_WARN it is useful to know whether or not the
system has been in a softlockup state when debugging.

[akpm@linux-foundation.org: apply the taint before calling panic()]
Signed-off-by: Josh Hunt <johunt@akamai.com>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/oops-tracing.txt

@@ -268,6 +268,8 @@ characters, each representing a particular tainted value.
  14: 'E' if an unsigned module has been loaded in a kernel supporting
      module signature.
 
+ 15: 'L' if a soft lockup has previously occurred on the system.
+
 The primary reason for the 'Tainted: ' string is to tell kernel
 debuggers if this is a clean kernel or if anything unusual has
 occurred.  Tainting is permanent: even if an offending module is

Documentation/sysctl/kernel.txt

@@ -826,6 +826,7 @@ can be ORed together:
 4096 - An out-of-tree module has been loaded.
 8192 - An unsigned module has been loaded in a kernel supporting module
        signature.
+16384 - A soft lockup has previously occurred on the system.
 
 ==============================================================
 

include/linux/kernel.h

@@ -470,6 +470,7 @@ extern enum system_states {
 #define TAINT_FIRMWARE_WORKAROUND	11
 #define TAINT_OOT_MODULE		12
 #define TAINT_UNSIGNED_MODULE		13
+#define TAINT_SOFTLOCKUP		14
 
 extern const char hex_asc[];
 #define hex_asc_lo(x)	hex_asc[((x) & 0x0f)]

kernel/panic.c

@@ -224,6 +224,7 @@ static const struct tnt tnts[] = {
 	{ TAINT_FIRMWARE_WORKAROUND,	'I', ' ' },
 	{ TAINT_OOT_MODULE,		'O', ' ' },
 	{ TAINT_UNSIGNED_MODULE,	'E', ' ' },
+	{ TAINT_SOFTLOCKUP,		'L', ' ' },
 };
 
 /**

kernel/watchdog.c

@@ -368,6 +368,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
 			smp_mb__after_atomic();
 		}
 
+		add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
 		if (softlockup_panic)
 			panic("softlockup: hung tasks");
 		__this_cpu_write(soft_watchdog_warn, true);