From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kent Overstreet Subject: Re: [PATCH 22/25] Generic dynamic per cpu refcounting Date: Thu, 29 Nov 2012 12:45:31 -0800 Message-ID: <20121129204531.GK15094@google.com> References: <1354121029-1376-23-git-send-email-koverstreet@google.com> <20121129185720.GE15094@google.com> <20121129185953.GW16230@one.firstfloor.org> <20121129191214.GG15094@google.com> <20121129192003.GX16230@one.firstfloor.org> <20121129192925.GH15094@google.com> <20121129193452.GI19042@kvack.org> <20121129202231.GJ15094@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Benjamin LaHaise , linux-kernel@vger.kernel.org, linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, zab@redhat.com, jmoyer@redhat.com, axboe@kernel.dk, viro@zeniv.linux.org.uk To: Andi Kleen Return-path: Content-Disposition: inline In-Reply-To: Sender: owner-linux-aio@kvack.org List-Id: linux-fsdevel.vger.kernel.org On Thu, Nov 29, 2012 at 12:42:17PM -0800, Andi Kleen wrote: > Kent Overstreet writes: > > > On Thu, Nov 29, 2012 at 02:34:52PM -0500, Benjamin LaHaise wrote: > >> On Thu, Nov 29, 2012 at 11:29:25AM -0800, Kent Overstreet wrote: > >> > There's some kind of symmetry going on here, and if I'd been awake more > >> > in college I could probably say exactly why it works, but it does. > >> > >> I think the catch is that using only a 32 bit counter is something the > >> user could arbitrarily control the sum of all parts. I think a 64 bit > >> counter may be required to ensure no overflow occurs. Otherwise, an > >> overflow could result in a premature free when there are still 2^32 > >> objects active thanks to a malicious user (possible on systems with lots > >> of memory these days -- remote, but possible). > > > > That's no different from regular atomic_t - but you're right, we > > should be using size_t for anything userspace can manipulate. > > The regular atomic_t is limited in ways that you are not. > See my original mail. I don't follow, can you explain? -- To unsubscribe, send a message with 'unsubscribe linux-aio' in the body to majordomo@kvack.org. For more info on Linux AIO, see: http://www.kvack.org/aio/ Don't email: aart@kvack.org