On Mon, 15 Jan 2024 11:09:38 -0500
Steven Rostedt <rost...@goodmis.org> wrote:
> No. The ring buffer logic should not care if the user of it is swapping
> the entire ring buffer or not. It only cares if parts of the ring
> buffer is being swapped or not. That's not the level of scope it should
> care about. If we do not want a swap to happen in update_max_tr()
> that's not ring_buffer.c's problem. The code to prevent that from
> happening should be 100% in trace.c.
What needs to be done, and feel free to add this as a separate patch,
is to have checks where snapshot is used.
(All errors return -EBUSY)
Before allowing mapping, check to see if:
1) the current tracer has "use_max_tr" set.
2) any event has a "snapshot" trigger set
3) Any function has a "snapshot" command set
Fail if any of the above is true.
Also in reverse, if the buffer is mapped, then fail:
1) a tracer being set that has "use_max_tr" set.
2) a "snapshot" command being set on a function
3) a "snapshot" trigger being set on an event.
For the last two, we may be able to get away with just a below as well.
Adding the tr->flags bit. We could also add a tr->snapshot count to
keep track of everything that is using a snapshot, and if that count is
non-zero, mapping fails.
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 2a7c6fd934e9..f534f74ae80f 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1175,6 +1175,12 @@ static void tracing_snapshot_instance_cond(struct
trace_array *tr,
return;
}
+ if (tr->flags & TRACE_ARRAY_FL_MAPPED) {
+ trace_array_puts(tr, "*** BUFFER IS MEMORY MAPPED ***\n");
+ trace_array_puts(tr, "*** Can not use snapshot (sorry) ***\n");
+ return;
+ }
+
local_irq_save(flags);
update_max_tr(tr, current, smp_processor_id(), cond_data);
local_irq_restore(flags);
-- Steve
