[PATCH] Fix: tracepoint: do not warn on ENOMEM

[Mathieu Desnoyers]

Tracepoint should only warn when a kernel API user does not respect the
required preconditions (e.g. same tracepoint enabled twice, or called
to remove a tracepoint that does not exist).

Silence warning in out-of-memory conditions, given that the error is
returned to the caller.

This ensures that out-of-memory error-injection testing does not trigger
warnings in tracepoint.c, which were seen by syzbot.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Reported-by: syzbot+9c0d616860575a73166a@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+4e9ae7fa46233396f64d@xxxxxxxxxxxxxxxxxxxxxxxxx
CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxxxxx>
CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CC: Jiri Olsa <jolsa@xxxxxxxxxx>
CC: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CC: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
CC: Namhyung Kim <namhyung@xxxxxxxxxx>
CC: stable@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/001a114465e241a8720567419a72@xxxxxxxxxx
Link: https://lkml.kernel.org/r/001a1140e0de15fc910567464190@xxxxxxxxxx
---
 kernel/tracepoint.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 671b13457387..1e37da2e0c25 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -207,7 +207,7 @@ static int tracepoint_add_func(struct tracepoint *tp,
 			lockdep_is_held(&tracepoints_mutex));
 	old = func_add(&tp_funcs, func, prio);
 	if (IS_ERR(old)) {
-		WARN_ON_ONCE(1);
+		WARN_ON_ONCE(PTR_ERR(old) != -ENOMEM);
 		return PTR_ERR(old);
 	}
 
@@ -239,7 +239,7 @@ static int tracepoint_remove_func(struct tracepoint *tp,
 			lockdep_is_held(&tracepoints_mutex));
 	old = func_remove(&tp_funcs, func);
 	if (IS_ERR(old)) {
-		WARN_ON_ONCE(1);
+		WARN_ON_ONCE(PTR_ERR(old) != -ENOMEM);
 		return PTR_ERR(old);
 	}
 
-- 
2.11.0