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Message-ID: <492fe2ae-5141-d548-ebd5-62f5fe2e57f7@I-love.SAKURA.ne.jp>
Date:   Wed, 7 Jun 2023 19:19:02 +0900
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Subject: [PATCH v2] debugobjects: recheck debug_objects_enabled before
 reporting
Content-Language: en-US
To:     Thomas Gleixner <tglx@linutronix.de>,
        syzbot <syzbot+7937ba6a50bdd00fffdf@syzkaller.appspotmail.com>,
        syzkaller-bugs@googlegroups.com
Cc:     linux-kernel@vger.kernel.org, Stephen Boyd <swboyd@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        wuchi <wuchi.zero@gmail.com>
References: <0000000000003a2f8505fcd5f06b@google.com>
 <1af29817-4698-c5ac-cf63-0dad289e740f@I-love.SAKURA.ne.jp>
 <871qiokyma.ffs@tglx>
From:   Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
In-Reply-To: <871qiokyma.ffs@tglx>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

syzbot is reporting false positive ODEBUG message immediately after
ODEBUG was disabled due to OOM. We should recheck debug_objects_enabled
before reporting.

  [ 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((unsigned long) addr); // Finds a bucket, but...
                                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");
  }

Reported-by: syzbot <syzbot+7937ba6a50bdd00fffdf@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=7937ba6a50bdd00fffdf
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
Changes in v2:
  No need to turn off debug_objects_enabled from debug_objects_oom().

 lib/debugobjects.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 984985c39c9b..ab3bbcb78471 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -498,6 +498,15 @@ static void debug_print_object(struct debug_obj *obj, char *msg)
 	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
+	 * 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;
-- 
2.18.4