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Tue, 10 Apr 2018 16:21:48 -0400 Received: from resqmta-ch2-07v.sys.comcast.net ([69.252.207.39]:58276 "EHLO resqmta-ch2-07v.sys.comcast.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752064AbeDJUVr (ORCPT ); Tue, 10 Apr 2018 16:21:47 -0400 Date: Tue, 10 Apr 2018 15:21:45 -0500 (CDT) From: Christopher Lameter X-X-Sender: cl@nuc-kabylake To: Matthew Wilcox cc: Eric Dumazet , linux-mm@kvack.org, Matthew Wilcox , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , linux-kernel@vger.kernel.org, Jan Kara , Jeff Layton , Mel Gorman , stable@vger.kernel.org Subject: Re: [PATCH 1/2] slab: __GFP_ZERO is incompatible with a constructor In-Reply-To: <20180410175011.GE3614@bombadil.infradead.org> Message-ID: References: <20180410125351.15837-1-willy@infradead.org> <20180410165054.GC3614@bombadil.infradead.org> <20180410173841.GD3614@bombadil.infradead.org> <20180410175011.GE3614@bombadil.infradead.org> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-CMAE-Envelope: MS4wfPUKRHkC95QsYrsIT/As+M4MSZCyYLCp+5Cst2swZujtOJoUrFHU7zC4Nl1QMG4754OssGAAdlEis2Jnkr3d5BnTplf67r8GdqdzQL8jAnjP5sRgI2Gc j3pmFYt3AdHvOHRJLzhj3b6Vcdmh+OYTekB9puRGA0tveYrtyPA3Ft/w1j9B/ZdSJymy1S31mOdgBqtTw7HPaz2WgJqwQqbgClGy0xiG6UJn81qgSKse348b yoKp+1qBggTOQLgWOuwmGEzvqJ6f78E3wgj/gvNiV8qyUr5R0i9k91YPOHiX36b4Jrz1tOHk4xRXy+vQwaItR4Z8VEVwR0PDXV34+9BsTgKRH8tV93DgPqrV cVGg6cvraYbImt7vG1iJ4DBWp3CBRNFit8iQGmZDHH/8ipyt8ogyGOvULfJQ/YrXm30yxzHYoJ7Out4N0By4ITrTbNlx90A2kU1AVUT0oIi3Bjob/SjagaSR 8myGqifIT2oxKk2KqJJEEQvQ9zWEEqcrkBcDiUMv9YXpDi0yV5fzydZGj41mOd1cM6avl+nNpRFrMrpTAjOouxI9aJpkOG/zqwwj/Q== Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Tue, 10 Apr 2018, Matthew Wilcox wrote: > > Objects can be freed and reused and still be accessed from code that > > thinks the object is the old and not the new object.... > > Yes, I know, that's the point of RCU typesafety. My point is that an > object *which has never been used* can't be accessed. So you don't *need* > a constructor. But the object needs to have the proper contents after it was released and re-allocated. Some objects may rely on contents (like list heads) surviving the realloc process because access must always be possible. validate_slab() checks on proper metadata content in a slab although it does not access the payload. So that may work you separate the payload init from the metadata init.