From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <550078AB.5030203@plexistor.com> Date: Wed, 11 Mar 2015 19:17:31 +0200 From: Boaz Harrosh MIME-Version: 1.0 Subject: Re: [PATCH] brd: Ensure that bio_vecs have size <= PAGE_SIZE References: <1426093353-23709-1-git-send-email-ross.zwisler@linux.intel.com> In-Reply-To: <1426093353-23709-1-git-send-email-ross.zwisler@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org To: Ross Zwisler , linux-kernel@vger.kernel.org Cc: "Roger C. Pao (Enmotus)" , linux-nvdimm@lists.01.org, Nick Piggin List-ID: On 03/11/2015 07:02 PM, Ross Zwisler wrote: > The functions copy_from_brd() and copy_to_brd() are written with an > assumption that the bio_vec they are given has size <= PAGE_SIZE. This > assumption is not enforced in any way, and if the bio_vec has size > larger than PAGE_SIZE data will just be lost. > > Such a situation can occur with I/Os generated from in-kernel sources, > or with coalesced bio_vecs. I wish you could show me where in Kernel this can happen. who "coalesced bio_vecs" ? what Kernel sources generate bio->b_size > PAGE_SIZE ? I did try to look and could not find any. Sorry for my slowness. In fact I know of a couple of places that would break if this is true > This bug was originally reported against > the pmem driver, where it was found using the Enmotus tiering engine. > This out-of-tree driver - none-gpl, with no source code - is the first I have heard of this. > Instead we should have brd explicitly tell the block layer that it can > handle data segments of at most PAGE_SIZE. > > Signed-off-by: Ross Zwisler > Reported-by: Hugh Daschbach > Cc: Roger C. Pao (Enmotus) > Cc: Boaz Harrosh > Cc: linux-nvdimm@lists.01.org > Cc: Nick Piggin > --- > drivers/block/brd.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/block/brd.c b/drivers/block/brd.c > index 898b4f256782..7e4873361b64 100644 > --- a/drivers/block/brd.c > +++ b/drivers/block/brd.c > @@ -490,6 +490,7 @@ static struct brd_device *brd_alloc(int i) > blk_queue_make_request(brd->brd_queue, brd_make_request); > blk_queue_max_hw_sectors(brd->brd_queue, 1024); > blk_queue_bounce_limit(brd->brd_queue, BLK_BOUNCE_ANY); > + blk_queue_max_segment_size(brd->brd_queue, PAGE_SIZE); The only place that I can find that uses _max_segment_size is when translating a bio list to an sg_list, where physical segments may coalesce. I have never seen it at the bio level > > brd->brd_queue->limits.discard_granularity = PAGE_SIZE; > brd->brd_queue->limits.max_discard_sectors = UINT_MAX; > Cheers Boaz