Don't trigger softlockup detector on network fs blocked tasks

Pulling the ethernet cable on a 2.6.27-rc system with NFS mounts
currently leads to an ongoing flood of soft lockup detector backtraces
for all tasks blocked on the NFS mounts when the hickup takes
longer than 120s.

I don't think NFS problems should be all that noisy.

Luckily there's a reasonably easy way to distingush this case.

Don't report task softlockup warnings for tasks in TASK_KILLABLE
state, which is used by the network file systems.

I believe this patch is a 2.6.27 candidate.
Signed-off-by: NAndi Kleen <ak@linux.intel.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/softlockup.c

@@ -180,6 +180,10 @@ static void check_hung_task(struct task_struct *t, unsigned long now)
 	if (t->flags & PF_FROZEN)
 		return;
 
+	/* Don't check for tasks waiting on network file systems like NFS */
+	if (t->state & TASK_KILLABLE)
+		return;
+
 	if (switch_count != t->last_switch_count || !t->last_switch_timestamp) {
 		t->last_switch_count = switch_count;
 		t->last_switch_timestamp = now;