perf: Differentiate exec() and non-exec() comm events

perf tools like 'perf report' can aggregate samples by comm strings,
which generally works.  However, there are other potential use-cases.
For example, to pair up 'calls' with 'returns' accurately (from branch
events like Intel BTS) it is necessary to identify whether the process
has exec'd.  Although a comm event is generated when an 'exec' happens
it is also generated whenever the comm string is changed on a whim
(e.g. by prctl PR_SET_NAME).  This patch adds a flag to the comm event
to differentiate one case from the other.

In order to determine whether the kernel supports the new flag, a
selection bit named 'exec' is added to struct perf_event_attr.  The
bit does nothing but will cause perf_event_open() to fail if the bit
is set on kernels that do not have it defined.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/537D9EBE.7030806@intel.com
Cc: Paul Mackerras <paulus@samba.org>
Cc: Dave Jones <davej@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 7 insertions, 3 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index b4c1d4685bf0..707617a8c0f6 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -707,7 +707,7 @@ extern int perf_register_guest_info_callbacks(struct perf_guest_info_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_comm(struct task_struct *tsk, bool exec);
 extern void perf_event_fork(struct task_struct *tsk);
 
 /* Callchains */
@@ -815,7 +815,7 @@ static inline int perf_unregister_guest_info_callbacks
 
 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_comm(struct task_struct *tsk, bool exec)  { }
 static inline void perf_event_fork(struct task_struct *tsk)             { }
 static inline void perf_event_init(void)                                { }
 static inline int  perf_swevent_get_recursion_context(void)             { return -1; }
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 221b2bde3723..ad86e1d7dbc2 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2379,7 +2379,11 @@ extern long do_fork(unsigned long, unsigned long, unsigned long, int __user *, i
 struct task_struct *fork_idle(int);
 extern pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags);
 
-extern void set_task_comm(struct task_struct *tsk, const char *from);
+extern void __set_task_comm(struct task_struct *tsk, const char *from, bool exec);
+static inline void set_task_comm(struct task_struct *tsk, const char *from)
+{
+        __set_task_comm(tsk, from, false);
+}
 extern char *get_task_comm(char *to, struct task_struct *tsk);
 
 #ifdef CONFIG_SMP