perf: Allow building PMU drivers as modules

This patch adds support for building PMU driver as module. It exports
the functions perf_pmu_{register,unregister}() and adds reference tracking
for the PMU driver module.

When the PMU driver is built as a module, each active event of the PMU
holds a reference to the driver module.

Signed-off-by: Yan, Zheng <zheng.z.yan@intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1395133004-23205-1-git-send-email-zheng.z.yan@intel.com
Cc: eranian@google.com
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 16 insertions, 0 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 3356abcfff18..af6dcf1d9e47 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -172,6 +172,7 @@ struct perf_event;
 struct pmu {
         struct list_head                entry;
 
+        struct module                   *module;
         struct device                   *dev;
         const struct attribute_group    **attr_groups;
         const char                      *name;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index f83a71a3e46d..5129b1201050 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -39,6 +39,7 @@
 #include <linux/hw_breakpoint.h>
 #include <linux/mm_types.h>
 #include <linux/cgroup.h>
+#include <linux/module.h>
 
 #include "internal.h"
 
@@ -3229,6 +3230,9 @@ static void __free_event(struct perf_event *event)
         if (event->ctx)
                 put_ctx(event->ctx);
 
+        if (event->pmu)
+                module_put(event->pmu->module);
+
         call_rcu(&event->rcu_head, free_event_rcu);
 }
 static void free_event(struct perf_event *event)
@@ -6551,6 +6555,7 @@ free_pdc:
         free_percpu(pmu->pmu_disable_count);
         goto unlock;
 }
+EXPORT_SYMBOL_GPL(perf_pmu_register);
 
 void perf_pmu_unregister(struct pmu *pmu)
 {
@@ -6572,6 +6577,7 @@ void perf_pmu_unregister(struct pmu *pmu)
         put_device(pmu->dev);
         free_pmu_context(pmu);
 }
+EXPORT_SYMBOL_GPL(perf_pmu_unregister);
 
 struct pmu *perf_init_event(struct perf_event *event)
 {
@@ -6585,6 +6591,10 @@ struct pmu *perf_init_event(struct perf_event *event)
         pmu = idr_find(&pmu_idr, event->attr.type);
         rcu_read_unlock();
         if (pmu) {
+                if (!try_module_get(pmu->module)) {
+                        pmu = ERR_PTR(-ENODEV);
+                        goto unlock;
+                }
                 event->pmu = pmu;
                 ret = pmu->event_init(event);
                 if (ret)
@@ -6593,6 +6603,10 @@ struct pmu *perf_init_event(struct perf_event *event)
         }
 
         list_for_each_entry_rcu(pmu, &pmus, entry) {
+                if (!try_module_get(pmu->module)) {
+                        pmu = ERR_PTR(-ENODEV);
+                        goto unlock;
+                }
                 event->pmu = pmu;
                 ret = pmu->event_init(event);
                 if (!ret)
@@ -6771,6 +6785,7 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 err_pmu:
         if (event->destroy)
                 event->destroy(event);
+        module_put(pmu->module);
 err_ns:
         if (event->ns)
                 put_pid_ns(event->ns);