perf: Fix perf_event_comm() vs. exec() assumption

perf_event_comm() assumes that set_task_comm() is only called on
exec(), and in particular that its only called on current.

Neither are true, as Dave reported a WARN triggered by set_task_comm()
being called on !current.

Separate the exec() hook from the comm hook.

Reported-by: Dave Jones <davej@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/20140521153219.GH5226@laptop.programming.kicks-ass.net
[ Build fix. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/fs/exec.c b/fs/exec.c
index 238b7aa26f68ab538df0cc219073a3d26541cc11..a038a41a3677d9582a72529de59b2c7435a1799d 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1110,6 +1110,7 @@ void setup_new_exec(struct linux_binprm * bprm)
        else
                set_dumpable(current->mm, suid_dumpable);
 
+       perf_event_exec();
        set_task_comm(current, kbasename(bprm->filename));
 
        /* Set the new mm task size. We have to do that late because it may

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 3ef6ea12806a297107ff65b2ad554f5176c8e301..9b5cd1992a88ccf8d5e15ca54936c6145ee0878f 100644 (file)
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -695,6 +695,7 @@ extern struct perf_guest_info_callbacks *perf_guest_cbs;
 extern int perf_register_guest_info_callbacks(struct perf_guest_info_callbacks *callbacks);
 extern int perf_unregister_guest_info_callbacks(struct perf_guest_info_callbacks *callbacks);
 
+extern void perf_event_exec(void);
 extern void perf_event_comm(struct task_struct *tsk);
 extern void perf_event_fork(struct task_struct *tsk);
 
@@ -772,7 +773,7 @@ extern void perf_event_enable(struct perf_event *event);
 extern void perf_event_disable(struct perf_event *event);
 extern int __perf_event_disable(void *info);
 extern void perf_event_task_tick(void);
-#else
+#else /* !CONFIG_PERF_EVENTS: */
 static inline void
 perf_event_task_sched_in(struct task_struct *prev,
                         struct task_struct *task)                      { }
@@ -802,6 +803,7 @@ static inline int perf_unregister_guest_info_callbacks
 (struct perf_guest_info_callbacks *callbacks)                          { return 0; }
 
 static inline void perf_event_mmap(struct vm_area_struct *vma)         { }
+static inline void perf_event_exec(void)                               { }
 static inline void perf_event_comm(struct task_struct *tsk)            { }
 static inline void perf_event_fork(struct task_struct *tsk)            { }
 static inline void perf_event_init(void)                               { }

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 440eefc67397e48f15b58bc8cf31712bec91286b..647698f919885dc7a30526d1502bdf904fdab9d3 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2970,6 +2970,22 @@ out:
        local_irq_restore(flags);
 }
 
+void perf_event_exec(void)
+{
+       struct perf_event_context *ctx;
+       int ctxn;
+
+       rcu_read_lock();
+       for_each_task_context_nr(ctxn) {
+               ctx = current->perf_event_ctxp[ctxn];
+               if (!ctx)
+                       continue;
+
+               perf_event_enable_on_exec(ctx);
+       }
+       rcu_read_unlock();
+}
+
 /*
  * Cross CPU call to read the hardware event
  */
@@ -5057,18 +5073,6 @@ static void perf_event_comm_event(struct perf_comm_event *comm_event)
 void perf_event_comm(struct task_struct *task)
 {
        struct perf_comm_event comm_event;
-       struct perf_event_context *ctx;
-       int ctxn;
-
-       rcu_read_lock();
-       for_each_task_context_nr(ctxn) {
-               ctx = task->perf_event_ctxp[ctxn];
-               if (!ctx)
-                       continue;
-
-               perf_event_enable_on_exec(ctx);
-       }
-       rcu_read_unlock();
 
        if (!atomic_read(&nr_comm_events))
                return;