[PATCH 6.1 104/127] debugobjects: Recheck debug_objects_enabled before reporting

Greg Kroah-Hartman
2023-08-09T10:57:16Z

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>

commit 8b64d420fe2450f82848178506d3e3a0bd195539 upstream.

syzbot is reporting false a positive ODEBUG message immediately after
ODEBUG was disabled due to OOM.

[ 1062.309646][T22911] ODEBUG: Out of memory. ODEBUG disabled
[ 1062.886755][ T5171] ------------[ cut here ]------------
[ 1062.892770][ T5171] ODEBUG: assert_init not available (active state 0) object: ffffc900056afb20 object type: timer_list hint: process_timeout+0x0/0x40

CPU 0 [ T5171] CPU 1 [T22911]
-------------- --------------
debug_object_assert_init() {
if (!debug_objects_enabled)
return;
db = get_bucket(addr);
lookup_object_or_alloc() {
debug_objects_enabled = 0;
return NULL;
}
debug_objects_oom() {
pr_warn("Out of memory. ODEBUG disabled\n");
// all buckets get emptied here, and
}
lookup_object_or_alloc(addr, db, descr, false, true) {
// this bucket is already empty.
return ERR_PTR(-ENOENT);
}
// Emits false positive warning.
debug_print_object(&o, "assert_init");
}

Recheck debug_object_enabled in debug_print_object() to avoid that.

Reported-by: syzbot <syzbot+7937ba6a50bdd00fffdf@syzkaller.appspotmail.com>
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/492fe2ae-5141-d548-ebd5-62f5fe2e57f7@I-love.SAKURA.ne.jp
Closes: https://syzkaller.appspot.com/bug?extid=7937ba6a50bdd00fffdf
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
lib/debugobjects.c | 9 +++++++++
1 file changed, 9 insertions(+)

--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -498,6 +498,15 @@ static void debug_print_object(struct de
const struct debug_obj_descr *descr = obj->descr;
static int limit;

+ /*
+ * Don't report if lookup_object_or_alloc() by the current thread
+ * failed because lookup_object_or_alloc()/debug_objects_oom() by a
+ * concurrent thread turned off debug_objects_enabled and cleared
+ * the hash buckets.
+ */
+ if (!debug_objects_enabled)
+ return;
+
if (limit < 5 && descr != descr_test) {
void *hint = descr->debug_hint ?
descr->debug_hint(obj->object) : NULL;