From: Guilherme G. Piccoli gpiccoli@igalia.com
[ Upstream commit 1adff542d67a2ed1120955cb219bfff8a9c53f59 ]
The panic notifier infrastructure executes registered callbacks when a panic event happens - such callbacks are executed in atomic context, with interrupts and preemption disabled in the running CPU and all other CPUs disabled. That said, mutexes in such context are not a good idea.
This patch replaces a regular mutex with a mutex_trylock safer approach; given the nature of the mutex used in the driver, it should be pretty uncommon being unable to acquire such mutex in the panic path, hence no functional change should be observed (and if it is, that would be likely a deadlock with the regular mutex).
Fixes: 2227b7c74634 ("coresight: add support for CPU debug module") Cc: Leo Yan leo.yan@linaro.org Cc: Mathieu Poirier mathieu.poirier@linaro.org Cc: Mike Leach mike.leach@linaro.org Cc: Suzuki K Poulose suzuki.poulose@arm.com Signed-off-by: Guilherme G. Piccoli gpiccoli@igalia.com Reviewed-by: Suzuki K Poulose suzuki.poulose@arm.com Signed-off-by: Suzuki K Poulose suzuki.poulose@arm.com Link: https://lore.kernel.org/r/20220427224924.592546-10-gpiccoli@igalia.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/hwtracing/coresight/coresight-cpu-debug.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/drivers/hwtracing/coresight/coresight-cpu-debug.c b/drivers/hwtracing/coresight/coresight-cpu-debug.c index 2f6f46ea68e9..ccd59ba26609 100644 --- a/drivers/hwtracing/coresight/coresight-cpu-debug.c +++ b/drivers/hwtracing/coresight/coresight-cpu-debug.c @@ -391,9 +391,10 @@ static int debug_notifier_call(struct notifier_block *self, int cpu; struct debug_drvdata *drvdata;
- mutex_lock(&debug_lock); + /* Bail out if we can't acquire the mutex or the functionality is off */ + if (!mutex_trylock(&debug_lock)) + return NOTIFY_DONE;
- /* Bail out if the functionality is disabled */ if (!debug_enable) goto skip_dump;
@@ -412,7 +413,7 @@ static int debug_notifier_call(struct notifier_block *self,
skip_dump: mutex_unlock(&debug_lock); - return 0; + return NOTIFY_DONE; }
static struct notifier_block debug_notifier = {