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

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Date:   Thu, 24 Aug 2017 12:39:09 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@...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>,
        "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 Wed, Aug 23, 2017 at 02:55:17PM +0900, Sergey Senozhatsky wrote:
> On (08/23/17 13:35), Boqun Feng wrote:
> > > KERN_CONT and "\n" should not be together. "\n" flushes the cont
> > > buffer immediately.
> > > 
> > 
> > Hmm.. Not quite familiar with printk() stuffs, but I could see several
> > usages of printk(KERN_CONT "...\n") in kernel.
> > 
> > Did a bit research myself, and I now think the inappropriate use is to
> > use a KERN_CONT printk *after* another printk ending with a "\n".
> 
> ah... I didn't check __print_lock_name(): it leaves unflushed cont buffer
> upon the return. sorry, your code is correct.
> 

So means printk(KERN_CON "..."); + printk(KERN_CONT "...\n") is a
correct usage, right? Thanks. Again, not familiar with printk stuff,
glad you can help me go through this ;-)

Regards,
Boqun

> 	-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
> > > > 
> 
> 

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