[PATCH] check for stack overflow in ___might_sleep

[Eric Sandeen <sandeen@redhat.com>]

Sometimes a "BUG: sleeping function called from invalid context"
message is not indicative of locking problems, but is the result
of a stack overflow corrupting the thread info.

Witness http://oss.sgi.com/archives/xfs/2014-02/msg00325.html
for example, which took a few go-rounds to sort out.

If we're printing the warning, things are wonky already, and
it'd be informative to check for the stack end corruption at this
point, too.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index b5797b7..4ef726c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7328,6 +7328,9 @@ void ___might_sleep(const char *file, int line, int preempt_offset)
 			in_atomic(), irqs_disabled(),
 			current->pid, current->comm);
 
+	if (task_stack_end_corrupted(current))
+		printk(KERN_EMERG "Thread overran stack, or stack corrupted\n");
+
 	debug_show_held_locks(current);
 	if (irqs_disabled())
 		print_irqtrace_events(current);