From 3fec4aecb311995189217e64d725cfe84a568de3 Mon Sep 17 00:00:00 2001
From: Daniel Thompson <daniel.thompson@linaro.org>
Date: Wed, 6 May 2020 17:42:23 +0100
Subject: [PATCH] kgdb: Fix spurious true from in_dbg_master()
Git-commit: 3fec4aecb311995189217e64d725cfe84a568de3
References: git-fixes
Patch-mainline: v5.8-rc1

Currently there is a small window where a badly timed migration could
cause in_dbg_master() to spuriously return true. Specifically if we
migrate to a new core after reading the processor id and the previous
core takes a breakpoint then we will evaluate true if we read
kgdb_active before we get the IPI to bring us to halt.

Fix this by checking irqs_disabled() first. Interrupts are always
disabled when we are executing the kgdb trap so this is an acceptable
prerequisite. This also allows us to replace raw_smp_processor_id()
with smp_processor_id() since the short circuit logic will prevent
warnings from PREEMPT_DEBUG.

Fixes: dcc7871128e9 ("kgdb: core changes to support kdb")
Suggested-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20200506164223.2875760-1-daniel.thompson@linaro.org
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Oliver Neukum <oneukum@suse.com>
---
 include/linux/kgdb.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/linux/kgdb.h
+++ b/include/linux/kgdb.h
@@ -317,7 +317,7 @@ extern void gdbstub_exit(int status);
 extern int			kgdb_single_step;
 extern atomic_t			kgdb_active;
 #define in_dbg_master() \
-	(raw_smp_processor_id() == atomic_read(&kgdb_active))
+	(irqs_disabled() && (smp_processor_id() == atomic_read(&kgdb_active)))
 extern bool dbg_is_early;
 extern void __init dbg_late_init(void);
 #else /* ! CONFIG_KGDB */