uprobes/perf: Avoid uprobe_apply() whenever possible

uprobe_perf_open/close call the costly uprobe_apply() every time,
we can avoid it if:

	- "nr_systemwide != 0" is not changed.

	- There is another process/thread with the same ->mm.

	- copy_proccess() does inherit_event(). dup_mmap() preserves the
	  inserted breakpoints.

	- event->attr.enable_on_exec == T, we can rely on uprobe_mmap()
	  called by exec/mmap paths.

	- tp_target is exiting. Only _close() checks PF_EXITING, I don't
	  think TRACE_REG_PERF_OPEN can hit the dying task too often.

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

1 files changed, 36 insertions, 6 deletions

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 2399f1416555..8dad2a92dee9 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -680,30 +680,60 @@ __uprobe_perf_filter(struct trace_uprobe_filter *filter, struct mm_struct *mm)
         return false;
 }
 
+static inline bool
+uprobe_filter_event(struct trace_uprobe *tu, struct perf_event *event)
+{
+        return __uprobe_perf_filter(&tu->filter, event->hw.tp_target->mm);
+}
+
 static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event)
 {
+        bool done;
+
         write_lock(&tu->filter.rwlock);
-        if (event->hw.tp_target)
+        if (event->hw.tp_target) {
+                /*
+                 * event->parent != NULL means copy_process(), we can avoid
+                 * uprobe_apply(). current->mm must be probed and we can rely
+                 * on dup_mmap() which preserves the already installed bp's.
+                 *
+                 * attr.enable_on_exec means that exec/mmap will install the
+                 * breakpoints we need.
+                 */
+                done = tu->filter.nr_systemwide ||
+                        event->parent || event->attr.enable_on_exec ||
+                        uprobe_filter_event(tu, event);
                 list_add(&event->hw.tp_list, &tu->filter.perf_events);
-        else
+        } else {
+                done = tu->filter.nr_systemwide;
                 tu->filter.nr_systemwide++;
+        }
         write_unlock(&tu->filter.rwlock);
 
-        uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
+        if (!done)
+                uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
 
         return 0;
 }
 
 static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event)
 {
+        bool done;
+
         write_lock(&tu->filter.rwlock);
-        if (event->hw.tp_target)
+        if (event->hw.tp_target) {
                 list_del(&event->hw.tp_list);
-        else
+                done = tu->filter.nr_systemwide ||
+                        (event->hw.tp_target->flags & PF_EXITING) ||
+                        uprobe_filter_event(tu, event);
+        } else {
                 tu->filter.nr_systemwide--;
+                done = tu->filter.nr_systemwide;
+        }
         write_unlock(&tu->filter.rwlock);
 
-        uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
+        if (!done)
+                uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
 
         return 0;
 }