linux-kernel - Re: [PATCH 1/1] rtmutex: Handle when top lock owner changes

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 for Android: free password hash cracker in your pocket

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

Message-ID: <20140604101612.0d47b399@gandalf.local.home>
Date:	Wed, 4 Jun 2014 10:16:12 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Brad Mouring" <bmouring@...com>
Cc:	linux-rt-users@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Clark Williams <williams@...hat.com>
Subject: Re: [PATCH 1/1] rtmutex: Handle when top lock owner changes

On Wed, 4 Jun 2014 08:05:25 -0500
"Brad Mouring" <bmouring@...com> wrote:

 >          A->L2
> 
> This is a slight variation on what I was seeing. To use the nomenclature
> that you proposed at the start, rewinding to the point
> 
>    A->L2->B->L3->C->L4->D
> 
> Let's assume things continue to unfold as you explain. Task is D,
> top_waiter is C. A is scheduled out and the chain shuffles.
> 
>        A->L2->B
> C->L4->D->'

But isn't that a lock ordering problem there?

If B can block on L3 owned by C, I see the following:

  B->L3->C->L4->D->L2->B

Deadlock!

In my scenario I was very careful to point out that the lock ordering
was: L1->L2->L3->L4

But you show that we can have both:

   L2-> ... ->L4

    and

   L4-> ... ->L2

Which is a reverse of lock ordering and a possible deadlock can occur.

-- Steve


> 
> So, we now have D blocking on L2 and L4 has waiters, C again. Also,
> since the codepath to have C block on L4 again is the same as the
> codepath from when it blocked on it in the first place, the location
> is the same since the stack (for what we care about) is the same.
> 
--
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/