kprobes: Skip kretprobe hit in NMI context to avoid deadlock

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>
Acked-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: David S. Miller <davem@davemloft.net>
Link: http://lkml.kernel.org/r/20140804031016.11433.65539.stgit@kbuild-fedora.novalocal
[ Minor edits for clarity. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 734e9a7..3995f54 100644 (file)
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1778,7 +1778,18 @@ static int pre_handler_kretprobe(struct kprobe *p, struct pt_regs *regs)
        unsigned long hash, flags = 0;
        struct kretprobe_instance *ri;
 
-       /*TODO: consider to only swap the RA after the last pre_handler fired */
+       /*
+        * To avoid deadlocks, prohibit return probing in NMI contexts,
+        * just skip the probe and increase the (inexact) 'nmissed'
+        * statistical counter, so that the user is informed that
+        * something happened:
+        */
+       if (unlikely(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);
        if (!hlist_empty(&rp->free_instances)) {