linux-kernel - [PATCH RFC] debugobjects: Make stack check warning more informative

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Message-Id: <20180723212531.202328-1-joel@joelfernandes.org>
Date:   Mon, 23 Jul 2018 14:25:31 -0700
From:   Joel Fernandes <joel@...lfernandes.org>
To:     linux-kernel@...r.kernel.org
Cc:     kernel-team@...roid.com,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yang Shi <yang.shi@...ux.alibaba.com>,
        Waiman Long <longman@...hat.com>,
        Arnd Bergmann <arnd@...db.de>, astrachan@...gle.com
Subject: [PATCH RFC] debugobjects: Make stack check warning more informative

From: "Joel Fernandes (Google)" <joel@...lfernandes.org>

Recently we debugged an issue where debugobject tracking was telling
us of an annotation issue. Turns out the issue was due to the object in
concern being on a different stack which was due to another issue.

Discussing with tglx, he suggested printing the pointers and the
location of the stack for the currently running task. This helped find
the object was on the wrong stack. I turned the resulting patch into
something upstreamable, so that the error message is more informative
and can help in debugging for similar issues in the future.

Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
 lib/debugobjects.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 994be4805cec..24c1df0d7466 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -360,9 +360,12 @@ static void debug_object_is_on_stack(void *addr, int onstack)
 
 	limit++;
 	if (is_on_stack)
-		pr_warn("object is on stack, but not annotated\n");
+		pr_warn("object %p is on stack %p, but NOT annotated.\n", addr,
+			 task_stack_page(current));
 	else
-		pr_warn("object is not on stack, but annotated\n");
+		pr_warn("object %p is NOT on stack %p, but annotated.\n", addr,
+			 task_stack_page(current));
+
 	WARN_ON(1);
 }
 
-- 
2.18.0.233.g985f88cf7e-goog