locking/lockdep: Avoid triggering hardlockup from debug_show_all_locks()

debug_show_all_locks() iterates all tasks and print held locks whole
holding tasklist_lock.  This can take a while on a slow console device
and may end up triggering NMI hardlockup detector if someone else ends
up waiting for tasklist_lock.

Touch the NMI watchdog while printing the held locks to avoid
spuriously triggering the hardlockup detector.

Signed-off-by: Tejun Heo <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 5fa1324a4f29a57901bdcf0ca81874a3dfd9a66c..52165904471963a7a70e6d2786ea88c64ecae431 100644 (file)
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -49,6 +49,7 @@
 #include <linux/gfp.h>
 #include <linux/random.h>
 #include <linux/jhash.h>
+#include <linux/nmi.h>
 
 #include <asm/sections.h>
 
@@ -4490,6 +4491,7 @@ retry:
                if (!unlock)
                        if (read_trylock(&tasklist_lock))
                                unlock = 1;
+               touch_nmi_watchdog();
        } while_each_thread(g, p);
 
        pr_warn("\n");