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Message-Id: <20200619141624.450359947@linuxfoundation.org>
Date: Fri, 19 Jun 2020 16:32:55 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org, Will Deacon <will@...nel.org>,
Douglas Anderson <dianders@...omium.org>,
Daniel Thompson <daniel.thompson@...aro.org>,
Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.9 081/128] kgdb: Fix spurious true from in_dbg_master()
From: Daniel Thompson <daniel.thompson@...aro.org>
[ Upstream commit 3fec4aecb311995189217e64d725cfe84a568de3 ]
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@...nel.org>
Link: https://lore.kernel.org/r/20200506164223.2875760-1-daniel.thompson@linaro.org
Reviewed-by: Douglas Anderson <dianders@...omium.org>
Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
include/linux/kgdb.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/kgdb.h b/include/linux/kgdb.h
index e465bb15912d..6be5545d3584 100644
--- 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 */
--
2.25.1
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