[PATCH 3.2 050/110] tracing/filter: Do not WARN on operand count going below zero

[Ben Hutchings]

3.2.71-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: "Steven Rostedt (Red Hat)" <rostedt@xxxxxxxxxxx>

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@xxxxxxxxxx

Reported-by: Vince Weaver <vincent.weaver@xxxxxxxxx>
Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 kernel/trace/trace_events_filter.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1358,7 +1358,9 @@ static int check_preds(struct filter_par
 		}
 		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) {

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