From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: [PATCH 22/25] Generic dynamic per cpu refcounting Date: Thu, 29 Nov 2012 20:20:03 +0100 Message-ID: <20121129192003.GX16230@one.firstfloor.org> References: <1354121029-1376-1-git-send-email-koverstreet@google.com> <1354121029-1376-23-git-send-email-koverstreet@google.com> <20121129185720.GE15094@google.com> <20121129185953.GW16230@one.firstfloor.org> <20121129191214.GG15094@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andi Kleen , linux-kernel@vger.kernel.org, linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, zab@redhat.com, bcrl@kvack.org, jmoyer@redhat.com, axboe@kernel.dk, viro@zeniv.linux.org.uk To: Kent Overstreet Return-path: Content-Disposition: inline In-Reply-To: <20121129191214.GG15094@google.com> Sender: owner-linux-aio@kvack.org List-Id: linux-fsdevel.vger.kernel.org > The trick is that we don't watch for the refcount hitting 0 until we're > shutting down - so this only works if you keep track of your initial > refcount. As long as we're not shutting down, we know the refcount can't > hit 0 because we haven't released the initial refcount. This seems dangerous to me: assume you have one CPU which always does get and another does put. So there may be 2^32 such operations without a kill and you wrap for real in a way that does not get corrected. Normally this can only happen if you have a lot of objects or CPUs are limited. But you don't have any limit on getting out-of-sync. You could make it 64bit, but then wraps could happen. -Andi -- 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