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kgdb: Fix spurious true from in_dbg_master()

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[ 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@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: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Daniel Thompson 2020-05-06 17:42:23 +01:00 committed by Greg Kroah-Hartman
parent bb3bcde17b
commit fb228bf21e
1 changed files with 1 additions and 1 deletions
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include/linux/kgdb.h
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@ -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 */