The hotplug lock is acquired and released in the etm4_disable_sysfs() function, which is a low-level function located in the ETM4 driver. This prevents us from a new solution for hotplug.
Firstly, hotplug callbacks cannot invoke etm4_disable_sysfs() to disable the source; otherwise, a deadlock issue occurs. The reason is that, in the hotplug flow, the kernel acquires the hotplug lock before calling callbacks. Subsequently, if coresight_disable_source() is invoked and it calls etm4_disable_sysfs(), the hotplug lock will be acquired twice, leading to a double lock issue.
Secondly, when hotplugging a CPU on or off, if we want to manipulate all components on a path attached to the CPU, we need to maintain atomicity for the entire path. Otherwise, a race condition may occur with users setting the same path via the Sysfs knobs, ultimately causing mess states in CoreSight components.
This patch moves the hotplug locking from etm4_disable_sysfs() into enable_source_store(). As a result, when users control the Sysfs knobs, the whole flow is protected by hotplug locking, ensuring it is mutual exclusive with hotplug callbacks.
Note, the paired function etm4_enable_sysfs() does not use hotplug locking, which is why this patch does not modify it.
Reviewed-by: Mike Leach mike.leach@linaro.org Signed-off-by: Leo Yan leo.yan@arm.com --- drivers/hwtracing/coresight/coresight-etm4x-core.c | 9 --------- drivers/hwtracing/coresight/coresight-sysfs.c | 7 +++++++ 2 files changed, 7 insertions(+), 9 deletions(-)
diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c index af2793cdb983c85f883efe10d7633f9cf718a44f..7bea3d2c6f49a2169b8e3de1cb07cc22147aae3a 100644 --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c @@ -1090,13 +1090,6 @@ static void etm4_disable_sysfs(struct coresight_device *csdev) { struct etmv4_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
- /* - * Taking hotplug lock here protects from clocks getting disabled - * with tracing being left on (crash scenario) if user disable occurs - * after cpu online mask indicates the cpu is offline but before the - * DYING hotplug callback is serviced by the ETM driver. - */ - cpus_read_lock(); raw_spin_lock(&drvdata->spinlock);
/* @@ -1110,8 +1103,6 @@ static void etm4_disable_sysfs(struct coresight_device *csdev)
cscfg_csdev_disable_active_config(csdev);
- cpus_read_unlock(); - /* * we only release trace IDs when resetting sysfs. * This permits sysfs users to read the trace ID after the trace diff --git a/drivers/hwtracing/coresight/coresight-sysfs.c b/drivers/hwtracing/coresight/coresight-sysfs.c index 72e9607fc6aea4663abf7d1f7f03f247ea060b83..781290d8ecd63ef7d568d8045d422d87c6221e6b 100644 --- a/drivers/hwtracing/coresight/coresight-sysfs.c +++ b/drivers/hwtracing/coresight/coresight-sysfs.c @@ -363,6 +363,13 @@ static ssize_t enable_source_store(struct device *dev, if (ret) return ret;
+ /* + * CoreSight hotplug callbacks in core layer control a activated path + * from its source to sink. Taking hotplug lock here protects a race + * condition with hotplug callbacks. + */ + guard(cpus_read_lock)(); + if (val) { ret = coresight_enable_sysfs(csdev); if (ret)