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.

[[e-mail]: apply the taint before calling panic()]
Signed-off-by: Josh Hunt <[e-mail]>
Cc: Jason Baron <[e-mail]>
Cc: Randy Dunlap <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/oops-tracing.txt

···
  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

···
 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

···
 #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

···
 	{ TAINT_FIRMWARE_WORKAROUND,	'I', ' ' },
 	{ TAINT_OOT_MODULE,		'O', ' ' },
 	{ TAINT_UNSIGNED_MODULE,	'E', ' ' },
+	{ TAINT_SOFTLOCKUP,		'L', ' ' },
 };
 
 /**

kernel/watchdog.c

···
 			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);