linux-kernel - [tip: core/debugobjects] debugobjects: Recheck debug_objects

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Message-ID: <168614044350.404.4585037016201397086.tip-bot2@tip-bot2>
Date:   Wed, 07 Jun 2023 12:20:43 -0000
From:   "tip-bot2 for Tetsuo Handa" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     syzbot <syzbot+7937ba6a50bdd00fffdf@...kaller.appspotmail.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: core/debugobjects] debugobjects: Recheck debug_objects_enabled
 before reporting

The following commit has been merged into the core/debugobjects branch of tip:

Commit-ID:     8b64d420fe2450f82848178506d3e3a0bd195539
Gitweb:        https://git.kernel.org/tip/8b64d420fe2450f82848178506d3e3a0bd195539
Author:        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
AuthorDate:    Wed, 07 Jun 2023 19:19:02 +09:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Wed, 07 Jun 2023 14:16:12 +02:00

debugobjects: Recheck debug_objects_enabled before reporting

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@...kaller.appspotmail.com>
Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Signed-off-by: Thomas Gleixner <tglx@...utronix.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
---
 lib/debugobjects.c |  9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 984985c..a517256 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 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;