[PATCH] ARM: probes: Don't stop the machine if we're in the debugger

[dianders@chromium.org (Douglas Anderson)]

If we're in kgdb then the machine is already stopped.  Trying to stop
it again will cause us to try to sleep, which is not allowed while in
kgdb.  To avoid this problem, only stop the machine when we're not in
kgdb.

Reported-by: Aapo Vienamo <avienamo@nvidia.com>
Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
---
 arch/arm/kernel/patch.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/arm/kernel/patch.c b/arch/arm/kernel/patch.c
index 69bda1a..abf30ec 100644
--- a/arch/arm/kernel/patch.c
+++ b/arch/arm/kernel/patch.c
@@ -1,5 +1,6 @@
 #include <linux/kernel.h>
 #include <linux/spinlock.h>
+#include <linux/kgdb.h>
 #include <linux/kprobes.h>
 #include <linux/mm.h>
 #include <linux/stop_machine.h>
@@ -124,6 +125,9 @@ void __kprobes patch_text(void *addr, unsigned int insn)
 		.insn = insn,
 	};
 
-	stop_machine(patch_text_stop_machine, &patch, NULL);
+	/* Stop machine before patching; but not if in the debugger */
+	if (unlikely(in_dbg_master()))
+		patch_text_stop_machine(&patch);
+	else
+		stop_machine(patch_text_stop_machine, &patch, NULL);
 }
-- 
2.5.0.457.gab17608