Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754692AbcC2VSh (ORCPT ); Tue, 29 Mar 2016 17:18:37 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:54312 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754389AbcC2VSg (ORCPT ); Tue, 29 Mar 2016 17:18:36 -0400 Date: Tue, 29 Mar 2016 14:18:33 -0700 From: Christoph Hellwig To: Shaohua Li Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, axboe@fb.com, Kernel-team@fb.com, "4.2+" , Ming Lei Subject: Re: [PATCH] block: don't make BLK_DEF_MAX_SECTORS too big Message-ID: <20160329211833.GA18532@infradead.org> References: <21cf85d32278bbe5acbc3def0a6db75db98a2670.1459269590.git.shli@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <21cf85d32278bbe5acbc3def0a6db75db98a2670.1459269590.git.shli@fb.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 821 Lines: 15 On Tue, Mar 29, 2016 at 09:42:33AM -0700, Shaohua Li wrote: > bio_alloc_bioset() allocates bvecs from bvec_slabs which can only > allocate maximum 256 bvec (eg, 1M for 4k pages). We can't bump > BLK_DEF_MAX_SECTORS to exceed this value otherwise bio_alloc_bioset will > fail. This might be true, but it's not a good enough reason. Request based driver couldn't care less about the limits of bio_alloc_bioset. It seems the bug is that somone (would be great to know whoe exactly) passes a too large value to bio_alloc_bioset. And given that we still have bio_add_page around for actually adding pages to a bio it seems like the proper fix would be to simply clamp down the actual allocation and segment limit inside bio_alloc_bioset. Which would also help to eventually remove code doing just that in tons of callers.