Re: [GIT PULL] tracing/uprobe: Fix uprobe_perf_open probes iteration

[Linus Torvalds]

On Wed, Nov 24, 2021 at 7:10 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> tracing: Fix wrong uprobe variable in iterator

I've pulled this, but:

>         list_for_each_entry(pos, trace_probe_probe_list(tp), list) {
> +               tu = container_of(pos, struct trace_uprobe, tp);

honestly, the "list_for_each_entry()" followed by a "container_of()"
like this makes me think you used the wrong entry to walk the list in.

You actually don't want to ever use that

        struct trace_probe *pos;

at all, and I think you should remove it.

Instead, you should do something like

        list_for_each_entry(pu, trace_probe_probe_list(tp), tp.list) {

ie simply walk the list _as_ the uprobe entry, not as some
intermediate internal probe list entry only to convert to the uprobe.

Now, I may be entirely off my meds here, and maybe there is something
I'm missing, but I _think_ the attached patch should work, and avoid
all that indirection through 'pos' that you don't care about and that
seems to just have been a mistake.

Feel free to call me funny names for when I missed some detail.

Again - I *have* pulled your fix, and in fact the attached patch is
relative to your fix. That fix isn't _wrong_. I just think it's a bit
silly, and I think the cause of the bug in the first place was that
unnecessary intermediate pointer.

               Linus
 kernel/trace/trace_uprobe.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index f5f0039d31e5..ee5408f2a68a 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -1300,7 +1300,7 @@ static int uprobe_perf_close(struct trace_event_call *call,
 static int uprobe_perf_open(struct trace_event_call *call,
 			    struct perf_event *event)
 {
-	struct trace_probe *pos, *tp;
+	struct trace_probe *tp;
 	struct trace_uprobe *tu;
 	int err = 0;
 
@@ -1312,8 +1312,7 @@ static int uprobe_perf_open(struct trace_event_call *call,
 	if (trace_uprobe_filter_add(tu->tp.event->filter, event))
 		return 0;
 
-	list_for_each_entry(pos, trace_probe_probe_list(tp), list) {
-		tu = container_of(pos, struct trace_uprobe, tp);
+	list_for_each_entry(tu, trace_probe_probe_list(tp), tp.list) {
 		err = uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
 		if (err) {
 			uprobe_perf_close(call, event);