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

From: Boqun Feng <[email-masked]>
Date: Thu, 24 Aug 2017 12:39:09 +0800

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
> > > > 
> 
>