linux-kernel - Re: [PATCH -v5][RFC]: mutex: implement adaptive spinning

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: <alpine.DEB.1.10.0901071844160.23456@gandalf.stny.rr.com>
Date:	Wed, 7 Jan 2009 18:46:28 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
cc:	Gregory Haskins <ghaskins@...ell.com>, Ingo Molnar <mingo@...e.hu>,
	Andi Kleen <andi@...stfloor.org>,
	Matthew Wilcox <matthew@....cx>,
	Peter Zijlstra <peterz@...radead.org>,
	paulmck@...ux.vnet.ibm.com, Chris Mason <chris.mason@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nick Piggin <npiggin@...e.de>,
	Peter Morreale <pmorreale@...ell.com>,
	Sven Dietrich <SDietrich@...ell.com>
Subject: Re: [PATCH -v5][RFC]: mutex: implement adaptive spinning


On Wed, 7 Jan 2009, Linus Torvalds wrote:
> On Wed, 7 Jan 2009, Steven Rostedt wrote:
> > 
> > What would be interesting is various benchmarks against all three.
> > 
> > 1) no mutex spinning.
> > 2) get_task_struct() implementation.
> > 3) spin_or_sched implementation.
> 
> One of the issues is that I cannot convince myself that (2) is even 
> necessarily correct. At least not without having all cases happen inder 
> the mutex spinlock - which they don't. Even with the original patch, the 
> uncontended cases set and cleared the owner field outside the lock.

True. I need to keep looking at the code that is posted. In -rt, we force 
the fast path into the slowpath as soon as another task fails to get the 
lock. Without that, as you pointed out, the code can be racy.

-- 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/