|
Message-ID: <20170424083250.h2wv2exbi4ytigac@hirez.programming.kicks-ass.net> Date: Mon, 24 Apr 2017 10:32:50 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Kees Cook <keescook@...omium.org> Cc: linux-kernel@...r.kernel.org, Eric Biggers <ebiggers3@...il.com>, Christoph Hellwig <hch@...radead.org>, "axboe@...nel.dk" <axboe@...nel.dk>, James Bottomley <James.Bottomley@...senpartnership.com>, Elena Reshetova <elena.reshetova@...el.com>, Hans Liljestrand <ishkamiel@...il.com>, David Windsor <dwindsor@...il.com>, x86@...nel.org, Ingo Molnar <mingo@...nel.org>, Arnd Bergmann <arnd@...db.de>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Jann Horn <jann@...jh.net>, davem@...emloft.net, linux-arch@...r.kernel.org, kernel-hardening@...ts.openwall.com, PaX Team <pageexec@...email.hu> Subject: Re: [PATCH] x86/refcount: Implement fast refcount_t handling On Fri, Apr 21, 2017 at 03:09:39PM -0700, Kees Cook wrote: > This patch ports the x86-specific atomic overflow handling from PaX's > PAX_REFCOUNT to the upstream refcount_t API. This is an updated version > from PaX that eliminates the saturation race condition by resetting the > atomic counter back to the INT_MAX saturation value on both overflow and > underflow. To win a race, a system would have to have INT_MAX threads > simultaneously overflow before the saturation handler runs. And is this impossible? Highly unlikely I'll grant you, but absolutely impossible? Also, you forgot nr_cpus in your bound. Afaict the worst case here is O(nr_tasks + 3*nr_cpus). Because PaX does it, is not a correctness argument. And this really wants one.
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.