On 08/13/2020 08:39 PM, Mathieu Poirier wrote:
On Fri, Aug 07, 2020 at 07:11:39PM +0800, Tingwei Zhang wrote:
From: Kim Phillips kim.phillips@arm.com
Allow to build coresight-etm4x as a module, for ease of development.
- Kconfig becomes a tristate, to allow =m
- append -core to source file name to allow module to be called coresight-etm4x by the Makefile
- add an etm4_remove function, for module unload
- add a MODULE_DEVICE_TABLE for autoloading on boot
- protect etmdrvdata[] with mutex lock from racing between module unload and CPU hotplug
Cc: Mathieu Poirier mathieu.poirier@linaro.org Cc: Leo Yan leo.yan@linaro.org Cc: Alexander Shishkin alexander.shishkin@linux.intel.com Cc: Randy Dunlap rdunlap@infradead.org Cc: Suzuki K Poulose Suzuki.Poulose@arm.com Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Russell King linux@armlinux.org.uk Signed-off-by: Kim Phillips kim.phillips@arm.com Signed-off-by: Tingwei Zhang tingwei@codeaurora.org Tested-by: Mike Leach mike.leach@linaro.org
drivers/hwtracing/coresight/Kconfig | 5 +- drivers/hwtracing/coresight/Makefile | 4 +- ...resight-etm4x.c => coresight-etm4x-core.c} | 118 +++++++++++++----- 3 files changed, 92 insertions(+), 35 deletions(-) rename drivers/hwtracing/coresight/{coresight-etm4x.c => coresight-etm4x-core.c} (95%)
diff --git a/drivers/hwtracing/coresight/Kconfig b/drivers/hwtracing/coresight/Kconfig index 8fd9fd139cf3..d6e107bbd30b 100644 --- a/drivers/hwtracing/coresight/Kconfig +++ b/drivers/hwtracing/coresight/Kconfig @@ -78,7 +78,7 @@ config CORESIGHT_SOURCE_ETM3X module will be called coresight-etm3x. config CORESIGHT_SOURCE_ETM4X
- bool "CoreSight Embedded Trace Macrocell 4.x driver"
- tristate "CoreSight Embedded Trace Macrocell 4.x driver" depends on ARM64 select CORESIGHT_LINKS_AND_SINKS select PID_IN_CONTEXTIDR
@@ -88,6 +88,9 @@ config CORESIGHT_SOURCE_ETM4X for instruction level tracing. Depending on the implemented version data tracing may also be available.
To compile this driver as a module, choose M here: themodule will be called coresight-etm4x.- config CORESIGHT_STM tristate "CoreSight System Trace Macrocell driver" depends on (ARM && !(CPU_32v3 || CPU_32v4 || CPU_32v4T)) || ARM64
diff --git a/drivers/hwtracing/coresight/Makefile b/drivers/hwtracing/coresight/Makefile index d619cfd0abd8..271dc255454f 100644 --- a/drivers/hwtracing/coresight/Makefile +++ b/drivers/hwtracing/coresight/Makefile @@ -14,8 +14,8 @@ obj-$(CONFIG_CORESIGHT_LINKS_AND_SINKS) += coresight-funnel.o \ obj-$(CONFIG_CORESIGHT_SOURCE_ETM3X) += coresight-etm3x.o coresight-etm3x-y := coresight-etm3x-core.o coresight-etm-cp14.o \ coresight-etm3x-sysfs.o -obj-$(CONFIG_CORESIGHT_SOURCE_ETM4X) += coresight-etm4x.o \
coresight-etm4x-sysfs.o+obj-$(CONFIG_CORESIGHT_SOURCE_ETM4X) += coresight-etm4x.o +coresight-etm4x-y := coresight-etm4x-core.o coresight-etm4x-sysfs.o obj-$(CONFIG_CORESIGHT_STM) += coresight-stm.o obj-$(CONFIG_CORESIGHT_CPU_DEBUG) += coresight-cpu-debug.o obj-$(CONFIG_CORESIGHT_CATU) += coresight-catu.o diff --git a/drivers/hwtracing/coresight/coresight-etm4x.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c similarity index 95% rename from drivers/hwtracing/coresight/coresight-etm4x.c rename to drivers/hwtracing/coresight/coresight-etm4x-core.c index fddfd93b9a7b..ae9847e194a3 100644 --- a/drivers/hwtracing/coresight/coresight-etm4x.c +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c @@ -48,6 +48,7 @@ module_param(pm_save_enable, int, 0444); MODULE_PARM_DESC(pm_save_enable, "Save/restore state on power down: 1 = never, 2 = self-hosted"); +static DEFINE_PER_CPU(struct mutex, etmdrvdata_lock); static struct etmv4_drvdata *etmdrvdata[NR_CPUS]; static void etm4_set_default_config(struct etmv4_config *config); static int etm4_set_event_filters(struct etmv4_drvdata *drvdata, @@ -1089,18 +1090,25 @@ void etm4_config_trace_mode(struct etmv4_config *config) static int etm4_online_cpu(unsigned int cpu) {
- if (!etmdrvdata[cpu])
- mutex_lock(&per_cpu(etmdrvdata_lock, cpu));
- if (!etmdrvdata[cpu]) {
mutex_unlock(&per_cpu(etmdrvdata_lock, cpu));- }
if (etmdrvdata[cpu]->boot_enable && !etmdrvdata[cpu]->sticky_enable) coresight_enable(etmdrvdata[cpu]->csdev);
- mutex_unlock(&per_cpu(etmdrvdata_lock, cpu)); return 0; }
static int etm4_starting_cpu(unsigned int cpu) {
- if (!etmdrvdata[cpu])
- mutex_lock(&per_cpu(etmdrvdata_lock, cpu));
- if (!etmdrvdata[cpu]) {
mutex_unlock(&per_cpu(etmdrvdata_lock, cpu));- }
spin_lock(&etmdrvdata[cpu]->spinlock); if (!etmdrvdata[cpu]->os_unlock) @@ -1109,18 +1117,23 @@ static int etm4_starting_cpu(unsigned int cpu) if (local_read(&etmdrvdata[cpu]->mode)) etm4_enable_hw(etmdrvdata[cpu]); spin_unlock(&etmdrvdata[cpu]->spinlock);
- mutex_unlock(&per_cpu(etmdrvdata_lock, cpu));
Ouch!
A mutex wrapping a spinlock to protect the exact same drvdata structure.
Actually this mutex is for "protecting" etmdrvdata[cpu], not the drvdata struct as such. But as you said, it becomes like a double lock.
Having mutex is an overkill for sure and can't be used replace spin_lock, especially if needed from atomic context. Having looked at the code, we only ever access/modify the etmdrvdata[cpu] on a different CPU is when we probe and there are chances of races. One of such is described here
http://lists.infradead.org/pipermail/linux-arm-kernel/2020-July/589941.html
I will see if I can spin a couple of patches to address these. Once we make sure that the etmdrvdata[cpu] is only modified by "cpu" then we don't need this mutex and stick with what we have.
Suzuki