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

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Date:   Thu, 29 Mar 2018 14:01:56 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc:     akpm@...ux-foundation.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().

On Thu, Mar 29, 2018 at 07:26:52PM +0900, Tetsuo Handa wrote:
> >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>

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Ingo, can you merge this?

> 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
>