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, 4 insertions, 1 deletions

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 301079d06f24..e2d4323c6ae6 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6162,11 +6162,14 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 
         if (task) {
                 event->attach_state = PERF_ATTACH_TASK;
+
+                if (attr->type == PERF_TYPE_TRACEPOINT)
+                        event->hw.tp_target = task;
 #ifdef CONFIG_HAVE_HW_BREAKPOINT
                 /*
                  * hw_breakpoint is a bit difficult here..
                  */
-                if (attr->type == PERF_TYPE_BREAKPOINT)
+                else if (attr->type == PERF_TYPE_BREAKPOINT)
                         event->hw.bp_target = task;
 #endif
         }