linux-kernel - Re: possible circular locking dependency detected [was: linux-next: Tree for Aug 22]

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Date:   Wed, 23 Aug 2017 13:46:48 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Boqun Feng <boqun.feng@...il.com>
Cc:     Byungchul Park <byungchul.park@....com>,
        Bart Van Assche <Bart.VanAssche@....com>,
        peterz@...radead.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "sergey.senozhatsky.work@...il.com" 
        <sergey.senozhatsky.work@...il.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
        "linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
        kernel-team@....com
Subject: Re: possible circular locking dependency detected [was: linux-next:
 Tree for Aug 22]

On (08/23/17 12:38), Boqun Feng wrote:
[..]
> diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
> index 642fb5362507..a3709e15f609 100644
> --- a/kernel/locking/lockdep.c
> +++ b/kernel/locking/lockdep.c
> @@ -1156,6 +1156,23 @@ print_circular_lock_scenario(struct held_lock *src,
>  		__print_lock_name(target);
>  		printk(KERN_CONT ");\n");

KERN_CONT and "\n" should not be together. "\n" flushes the cont
buffer immediately.

	-ss

>  		printk("\n *** DEADLOCK ***\n\n");
> +	} else if (cross_lock(src->instance)) {
> +		printk(" Possible unsafe locking scenario by crosslock:\n\n");
> +		printk("       CPU0                    CPU1\n");
> +		printk("       ----                    ----\n");
> +		printk("  lock(");
> +		__print_lock_name(target);
> +		printk(KERN_CONT ");\n");
> +		printk("  lock(");
> +		__print_lock_name(source);
> +		printk(KERN_CONT ");\n");
> +		printk("                               lock(");
> +		__print_lock_name(parent == source ? target : parent);
> +		printk(KERN_CONT ");\n");
> +		printk("                               unlock(");
> +		__print_lock_name(source);
> +		printk(KERN_CONT ");\n");
> +		printk("\n *** DEADLOCK ***\n\n");
>  	} else {
>  		printk(" Possible unsafe locking scenario:\n\n");
>  		printk("       CPU0                    CPU1\n");
> -- 
> 2.14.1
>