[PATCH] uprobes: get rid of bogus trace_uprobe hit counter

[Andrii Nakryiko]

trace_uprobe->nhit counter is not incremented atomically, so its value
is bogus in practice. On the other hand, it's actually a pretty big
uprobe scalability problem due to heavy cache line bouncing between CPUs
triggering the same uprobe.

Drop it and emit obviously unrealistic value in its stead in
uporbe_profiler seq file.

The alternative would be allocating per-CPU counter, but I'm not sure
it's justified.

Signed-off-by: Andrii Nakryiko <and...@kernel.org>
---
 kernel/trace/trace_uprobe.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 52e76a73fa7c..5d38207db479 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -62,7 +62,6 @@ struct trace_uprobe {
        struct uprobe                   *uprobe;
        unsigned long                   offset;
        unsigned long                   ref_ctr_offset;
-       unsigned long                   nhit;
        struct trace_probe              tp;
 };
 
@@ -821,7 +820,7 @@ static int probes_profile_seq_show(struct seq_file *m, void 
*v)
 
        tu = to_trace_uprobe(ev);
        seq_printf(m, "  %s %-44s %15lu\n", tu->filename,
-                       trace_probe_name(&tu->tp), tu->nhit);
+                  trace_probe_name(&tu->tp), ULONG_MAX);
        return 0;
 }
 
@@ -1507,7 +1506,6 @@ static int uprobe_dispatcher(struct uprobe_consumer *con, 
struct pt_regs *regs)
        int ret = 0;
 
        tu = container_of(con, struct trace_uprobe, consumer);
-       tu->nhit++;
 
        udd.tu = tu;
        udd.bp_addr = instruction_pointer(regs);
-- 
2.43.5