mips,kgdb: fix recursive page fault with CONFIG_KPROBES

This fault was detected using the kgdb test suite on boot and it
crashes recursively due to the fact that CONFIG_KPROBES on mips adds
an extra die notifier in the page fault handler.  The crash signature
looks like this:

kgdbts:RUN bad memory access test
KGDB: re-enter exception: ALL breakpoints killed
Call Trace:
[<807b7548>] dump_stack+0x20/0x54
[<807b7548>] dump_stack+0x20/0x54

The fix for now is to have kgdb return immediately if the fault type
is DIE_PAGE_FAULT and allow the kprobe code to decide what is supposed
to happen.

Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: <stable@vger.kernel.org>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/arch/mips/kernel/kgdb.c b/arch/mips/kernel/kgdb.c
index f4546e97c60..23817a6e32b 100644
--- a/arch/mips/kernel/kgdb.c
+++ b/arch/mips/kernel/kgdb.c
@@ -283,6 +283,15 @@ static int kgdb_mips_notify(struct notifier_block *self, unsigned long cmd,
         struct pt_regs *regs = args->regs;
         int trap = (regs->cp0_cause & 0x7c) >> 2;
 
+#ifdef CONFIG_KPROBES
+        /*
+         * Return immediately if the kprobes fault notifier has set
+         * DIE_PAGE_FAULT.
+         */
+        if (cmd == DIE_PAGE_FAULT)
+                return NOTIFY_DONE;
+#endif /* CONFIG_KPROBES */
+
         /* Userspace events, ignore. */
         if (user_mode(regs))
                 return NOTIFY_DONE;