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 <ross.zwis...@linux.intel.com> > Reported-by: Hugh Daschbach <hugh.daschb...@enmotus.com> > Cc: Roger C. Pao (Enmotus) <rcpao.enmo...@gmail.com> > Cc: Boaz Harrosh <b...@plexistor.com> > Cc: linux-nvd...@lists.01.org > Cc: Nick Piggin <npig...@kernel.dk> > --- > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
