linux-kernel - Re: [PATCH v2] lockdep: Show address of "struct lockdep_map" at print

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Message-Id: <201803291926.FEH43221.VSOQHOtFJFLMOF@I-love.SAKURA.ne.jp>
Date:   Thu, 29 Mar 2018 19:26:52 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     akpm@...ux-foundation.org
Cc:     peterz@...radead.org, mhocko@...e.com, mingo@...hat.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, bp@...e.de,
        rientjes@...gle.com, tglx@...utronix.de
Subject: Re: [PATCH v2] lockdep: Show address of "struct lockdep_map" at print_lock().

>>From 91c081c4c5f6a99402542951e7de661c38f928ab Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Date: Tue, 27 Mar 2018 19:38:33 +0900
Subject: [PATCH v2] lockdep: Show address of "struct lockdep_map" at print_lock().

Since "struct lockdep_map" is embedded into lock objects, we can know
which instance of a lock object is acquired using hlock->instance field.
This will help finding which threads are causing a lock contention.

Currently, print_lock() is printing hlock->acquire_ip field in both
"[<%px>]" and "%pS" format. But "[<%px>]" is little useful nowadays, for
we use scripts/faddr2line which receives "%pS" for finding the location
in the source code. And I want to reduce amount of output, for
debug_show_all_locks() might print a lot.

Therefore, this patch replaces "[<%px>]" for printing hlock->acquire_ip
field with "%p" for printing hlock->instance field.

[  251.305475] 3 locks held by a.out/31106:
[  251.308949]  #0: 00000000b0f753ba (&mm->mmap_sem){++++}, at: copy_process.part.41+0x10d5/0x1fe0
[  251.314283]  #1: 00000000ef64d539 (&mm->mmap_sem/1){+.+.}, at: copy_process.part.41+0x10fe/0x1fe0
[  251.319618]  #2: 00000000b41a282e (&mapping->i_mmap_rwsem){++++}, at: copy_process.part.41+0x12f2/0x1fe0

Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Acked-by: Michal Hocko <mhocko@...e.com>
Acked-by: David Rientjes <rientjes@...gle.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...e.de>
Cc: Thomas Gleixner <tglx@...utronix.de>
---
 kernel/locking/lockdep.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 12a2805..0233863 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -556,9 +556,9 @@ static void print_lock(struct held_lock *hlock)
 		return;
 	}
 
+	printk(KERN_CONT "%p", hlock->instance);
 	print_lock_name(lock_classes + class_idx - 1);
-	printk(KERN_CONT ", at: [<%px>] %pS\n",
-		(void *)hlock->acquire_ip, (void *)hlock->acquire_ip);
+	printk(KERN_CONT ", at: %pS\n", (void *)hlock->acquire_ip);
 }
 
 static void lockdep_print_held_locks(struct task_struct *curr)
-- 
1.8.3.1