linux-kernel - Re: 3.4.4-rt13: btrfs + xfstests 006 = BOOM.. and a bonus rt_mutex deadlock report for absolutely free!

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: <1342458195.2783.5.camel@acer.local.home>
Date:	Mon, 16 Jul 2012 13:03:15 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mike Galbraith <efault@....de>
Cc:	Chris Mason <chris.mason@...ionio.com>,
	"Chris L. Mason" <clmason@...ionio.com>,
	"linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: 3.4.4-rt13: btrfs + xfstests 006 = BOOM..  and a bonus
 rt_mutex deadlock report for absolutely free!

On Mon, 2012-07-16 at 18:36 +0200, Mike Galbraith wrote:
>  
> > > Ouch, you just turned the rt_read_lock() into a spin lock. If a higher
> > > priority process preempted a lower priority process that holds the same
> > > lock, it will deadlock.
> > 
> > Hm, how, it's doing cpu_chill()?
> 
> 'course PI is toast, so *poof*.  Since just enabling the lockdep bits
> seems to fix it up, maybe that's the patchlet to submit (less is more).

There's that too. But the issue I was talking about is with all trylock
loops. As holding an rt-mutex now disables migration, if a high priority
process preempts a task that holds the lock, and then the high prio task
starts spinning waiting for that lock to release, the lower priority
process will never get to run to release it. The cpu_chill() doesn't
help.

-- Steve


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/