perf: Introduce hw_perf_event->tp_target and ->tp_list

sys_perf_event_open()->perf_init_event(event) is called before
find_get_context(event), this means that event->ctx == NULL when
class->reg(TRACE_REG_PERF_REGISTER/OPEN) is called and thus it
can't know if this event is per-task or system-wide.

This patch adds hw_perf_event->tp_target for PERF_TYPE_TRACEPOINT,
this is analogous to PERF_TYPE_BREAKPOINT/bp_target we already have.
The patch also moves ->bp_target up so that it can overlap with the
new member, this can help the compiler to generate the better code.

trace_uprobe_register() will use it for prefiltering to avoid the
unnecessary breakpoints in mm's we do not want to trace.

->tp_target doesn't have its own reference, but we can rely on the
fact that either sys_perf_event_open() holds a reference, or it is
equal to event->ctx->task. So this pointer is always valid until
free_event().

Also add the "struct list_head tp_list" into this union. It is not
strictly necessary, but it can simplify the next changes and we can
add it for free.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 42adf012145d..e47ee462c2f2 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -135,16 +135,21 @@ struct hw_perf_event {
                 struct { /* software */
                         struct hrtimer  hrtimer;
                 };
+                struct { /* tracepoint */
+                        struct task_struct      *tp_target;
+                        /* for tp_event->class */
+                        struct list_head        tp_list;
+                };
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
                 struct { /* breakpoint */
-                        struct arch_hw_breakpoint       info;
-                        struct list_head                bp_list;
                         /*
                          * Crufty hack to avoid the chicken and egg
                          * problem hw_breakpoint has with context
                          * creation and event initalization.
                          */
                         struct task_struct              *bp_target;
+                        struct arch_hw_breakpoint       info;
+                        struct list_head                bp_list;
                 };
 #endif
         };