linux-kernel - Re: [rfc] "fair" rw spinlocks

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: <20091128152026.GA6883@linux.vnet.ibm.com>
Date:	Sat, 28 Nov 2009 07:20:26 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [rfc] "fair" rw spinlocks

On Sat, Nov 28, 2009 at 12:15:07PM +0100, Andi Kleen wrote:
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> writes:
> >
> > The usual trick would be to keep per-fair-rwlock state in per-CPU
> > variables.  If it is forbidden to read-acquire one nestable fair rwlock
> > while read-holding another, then this per-CPU state can be a single
> > pointer and a nesting count.  On the other hand, if it is permitted to
> > read-acquire one nestable fair rwlock while holding another, then one
> > can use a small per-CPU array of pointer/count pairs.
> 
> The problem is that in preemptible kernels kernel threads can switch
> CPUs all the time.  How would you sync the per CPU state then?

In preemptible kernels, put the state into the task structure.  Perhaps do
this in non-preemptible kernels too, just to save a bit of source code.

							Thanx, Paul
--
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/