tracepoint: Do not warn on ENOMEM

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@google.com
Link: https://lkml.kernel.org/r/001a1140e0de15fc910567464190@google.com
Link: http://lkml.kernel.org/r/20180315124424.32319-1-mathieu.desnoyers@efficios.com

CC: Peter Zijlstra <peterz@infradead.org>
CC: Jiri Olsa <jolsa@redhat.com>
CC: Arnaldo Carvalho de Melo <acme@kernel.org>
CC: Alexander Shishkin <alexander.shishkin@linux.intel.com>
CC: Namhyung Kim <namhyung@kernel.org>
CC: stable@vger.kernel.org
Fixes: de7b2973903c6 ("tracepoint: Use struct pointer instead of name hash for reg/unreg tracepoints")
Reported-by: syzbot+9c0d616860575a73166a@syzkaller.appspotmail.com
Reported-by: syzbot+4e9ae7fa46233396f64d@syzkaller.appspotmail.com
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

1 files 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);
         }