[PATCH 3.16 245/366] tracepoint: Do not warn on ENOMEM

[Ben Hutchings]

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

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

From: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>

commit d66a270be3310d7aa132fec0cea77d3d32a0ff75 upstream.

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.

Link: https://lkml.kernel.org/r/001a114465e241a8720567419a72@xxxxxxxxxx
Link: https://lkml.kernel.org/r/001a1140e0de15fc910567464190@xxxxxxxxxx
Link: http://lkml.kernel.org/r/20180315124424.32319-1-mathieu.desnoyers@xxxxxxxxxxxx

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>
Fixes: de7b2973903c6 ("tracepoint: Use struct pointer instead of name hash for reg/unreg tracepoints")
Reported-by: syzbot+9c0d616860575a73166a@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+4e9ae7fa46233396f64d@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 kernel/tracepoint.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -185,7 +185,7 @@ static int tracepoint_add_func(struct tr
 			lockdep_is_held(&tracepoints_mutex));
 	old = func_add(&tp_funcs, func);
 	if (IS_ERR(old)) {
-		WARN_ON_ONCE(1);
+		WARN_ON_ONCE(PTR_ERR(old) != -ENOMEM);
 		return PTR_ERR(old);
 	}
 
@@ -218,7 +218,7 @@ static int tracepoint_remove_func(struct
 			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);
 	}