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From:   Stephen Boyd <swboyd@chromium.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     linux-kernel@vger.kernel.org, patches@lists.linux.dev,
        Guenter Roeck <groeck@chromium.org>
Subject: [PATCH] debugobjects: Print object pointer in debug_print_object()
Date:   Thu, 19 May 2022 13:22:01 -0700
Message-Id: <20220519202201.2348343-1-swboyd@chromium.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Delayed kobject debugging (CONFIG_DEBUG_KOBJECT_RELEASE) prints the
kobject pointer that's being released in kobject_release() before
scheduling a randomly delayed work to do the actual release work. If the
caller of kobject_put() frees the kobject upon return then we'll
typically see a debugobject warning about freeing an active timer.
Usually the release function is the function that does the kfree() of
the struct containing the kobject.

For example the following print is seen

 kobject: 'queue' (ffff888114236190): kobject_release, parent 0000000000000000 (delayed 1000)
 ------------[ cut here ]------------
 ODEBUG: free active (active state 0) object type: timer_list hint: kobject_delayed_cleanup+0x0/0x390

but we can't match up the kobject printk with the debug object printk
because it could be any number of kobjects that was released around that
time. The random delay for the work doesn't help either.

Print the address of the object being tracked to help us figure out
which kobject is the problem here. Note that we don't use %px here to
match the other %p usage in debugobject debugging. Due to %p usage we'll
have to disable pointer hashing to correlate the two pointer printks.

Cc: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
---
 lib/debugobjects.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 6946f8e204e3..a1c987e967e0 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -503,9 +503,9 @@ static void debug_print_object(struct debug_obj *obj, char *msg)
 			descr->debug_hint(obj->object) : NULL;
 		limit++;
 		WARN(1, KERN_ERR "ODEBUG: %s %s (active state %u) "
-				 "object type: %s hint: %pS\n",
+				 "object: %p object type: %s hint: %pS\n",
 			msg, obj_states[obj->state], obj->astate,
-			descr->name, hint);
+			obj->object, descr->name, hint);
 	}
 	debug_objects_warnings++;
 }

base-commit: ffb217a13a2eaf6d5bd974fc83036a53ca69f1e2
-- 
https://chromeos.dev