tracing/filter: Do not WARN on operand count going below zero

commit b4875bbe7e68f139bd3383828ae8e994a0df6d28 upstream.

When testing the fix for the trace filter, I could not come up with
a scenario where the operand count goes below zero, so I added a
WARN_ON_ONCE(cnt < 0) to the logic. But there is legitimate case
that it can happen (although the filter would be wrong).

 # echo '>' > /sys/kernel/debug/events/ext4/ext4_truncate_exit/filter

That is, a single operation without any operands will hit the path
where the WARN_ON_ONCE() can trigger. Although this is harmless,
and the filter is reported as a error. But instead of spitting out
a warning to the kernel dmesg, just fail nicely and report it via
the proper channels.

Link: http://lkml.kernel.org/r/558C6082.90608@oracle.com
Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Zefan Li <lizefan@huawei.com>

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 3b04aec58700ce5e860474998f8f3d00de0ee182..ae6c5722efb99039bc1c8171ec63b92df00a2357 100644 (file)
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1372,7 +1372,9 @@ static int check_preds(struct filter_parse_state *ps)
                }
                cnt--;
                n_normal_preds++;
-               WARN_ON_ONCE(cnt < 0);
+               /* all ops should have operands */
+               if (cnt < 0)
+                       break;
        }
 
        if (cnt != 1 || !n_normal_preds || n_logical_preds >= n_normal_preds) {