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Date: Wed, 23 Aug 2017 14:55:17 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
	Byungchul Park <byungchul.park@lge.com>,
	Bart Van Assche <Bart.VanAssche@wdc.com>, peterz@infradead.org,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
	"axboe@kernel.dk" <axboe@kernel.dk>,
	"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
	"sfr@canb.auug.org.au" <sfr@canb.auug.org.au>,
	"linux-next@vger.kernel.org" <linux-next@vger.kernel.org>,
	kernel-team@lge.com
Subject: Re: possible circular locking dependency detected [was: linux-next:
 Tree for Aug 22]
Message-ID: <20170823055517.GB728@jagdpanzerIV.localdomain>
References: <20170822183816.7925e0f8@canb.auug.org.au>
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 <1503438234.2508.27.camel@wdc.com>
 <20170823000304.GK20323@X58A-UD3R>
 <20170823034951.GG11771@tardis>
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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.

	-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
> > >