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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20170823053501.GJ11771@tardis>
Date:   Wed, 23 Aug 2017 13:35:01 +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 01:46:48PM +0900, Sergey Senozhatsky wrote:
> 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.
> 

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". Am I
missing some recent changes or rules of KERN_CONT?

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
> > 

Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)