[PATCH -tip ] [BUGFIX] kprobes: Skip kretprobe hit in NMI context to avoid deadlock

[Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>]

Skip kretprobe hit in NMI context, because if an NMI happens
inside the critical section protected by kretprobe_table.lock
and another(or same) kretprobe hit, pre_kretprobe_handler
tries to lock kretprobe_table.lock again.
Normal interrupts have no problem because they are disabled
with the lock.

Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: "David S. Miller" <davem@davemloft.net>
---
 kernel/kprobes.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 734e9a7..a537029 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1778,6 +1778,12 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
 	unsigned long hash, flags = 0;
 	struct kretprobe_instance *ri;
 
+	/* To avoid deadlock, prohibit return probing in NMI context */
+	if (in_nmi()) {
+		rp->nmissed++;
+		return 0;
+	}
+
 	/*TODO: consider to only swap the RA after the last pre_handler fired */
 	hash = hash_ptr(current, KPROBE_HASH_BITS);
 	raw_spin_lock_irqsave(&rp->lock, flags);