On Wed, Apr 06, 2016 at 08:59:31AM +0800, Ming Lei wrote: > On Wed, Apr 6, 2016 at 8:30 AM, Kent Overstreet > <kent.overstreet@xxxxxxxxx> wrote: > > On Wed, Apr 06, 2016 at 01:44:06AM +0800, Ming Lei wrote: > >> After arbitrary bio size is supported, the incoming bio may > >> be very big. We have to split the bio into small bios so that > >> each holds at most BIO_MAX_PAGES bvecs for safety reason, such > >> as bio_clone(). > >> > >> This patch fixes the following kernel crash: > > > > Ming, let's not do it this way; drivers that don't clone biovecs are the norm - > > instead, md has its own queue limits that it ought to be setting up correctly. > > Except for md, there are also several usages of bio_clone: > > - drbd > - osdblk > - pktcdvd > - xen-blkfront > - verify code of bcache > > I don't like bio_clone() too, which can cause trouble to multipage bvecs. > > How about fixing the issue by this simple patch first? Then once we limits > all above queues by max sectors, the global limit can be removed as > mentioned by the comment. just do this: void blk_set_limit_clonable(struct queue_limits *lim) { lim->max_segments = min(lim->max_segments, BIO_MAX_PAGES); } and then call that from the appropriate drivers. It should be like 20 minutes of work. My issue is that your approach of just enforcing a global limit is a step in the wrong direction - we want to get _away_ from that and move towards drivers specifying _directly_ what their limits are: more straightforward, less opaque. Also, your patch is wrong, as it'll break if there's bvecs that aren't full pages. -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html