On Thu, 18 Mar 2010 11:48:58 -0700 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > On Mon, 8 Mar 2010 14:14:49 +0100 > Lars Ellenberg <lars.ellenberg@xxxxxxxxxx> wrote: > > > On Mon, Mar 08, 2010 at 03:35:37AM -0500, Mikulas Patocka wrote: > > > Hi > > > > > > That patch with limits->max_segments = 1; is wrong. It fixes this bug > > > sometimes and sometimes not. > > > > > > The problem is, if someone attempts to create a bio with two vector > > > entries, the first maps the last sector contained in some page and the > > > second maps the first sector of the next physical page: it has one > > > segment, it has size <= PAGE_SIZE, but it still may cross raid stripe and > > > the raid driver will reject it. > > > > Now that you put it that way ;) > > You are right. > > > > My asumption that "single segment" was > > equalvalent in practice with "single bvec" > > does not hold true in that case. > > > > Then, what about adding seg_boundary_mask restrictions as well? > > max_sectors = PAGE_SIZE >> 9; > > max_segments = 1; > > seg_boundary_mask = PAGE_SIZE -1; > > or some such. > > > > > > > This is not the first time this has been patched, btw. > > > > > See https://bugzilla.redhat.com/show_bug.cgi?id=440093 > > > > > and the patch by Mikulas: > > > > > https://bugzilla.redhat.com/attachment.cgi?id=342638&action=diff > > > > > > Look at this patch, it is the proper way how to fix it: create a > > > merge_bvec_fn that reject more than one biovec entry. > > > > If adding seg_boundary_mask is still not sufficient, > > lets merge that patch instead? > > Why has it been dropped, respectively never been merged? > > It became obsolete for dm-linear by 7bc3447b, > > but in general the bug is still there, or am I missing something? > > > > This all seemed to die. Does Neil's mysterypatch fix all these issues? > > Neil, was that patch tagged for -stable backporting? The patch at the top of my 'for-linus' branch (which Linus doesn't seem to have pulled yet) fixes this for md and is tagged for -stable backporting. I just sets max_segments and seg_boundary_mask. There is no point setting max_sectors as well. I found that setting merge_bvec_fn, while a perfectly correct approach, was more cumbersome. My patch doesn't fix this for dm. I assume the dm developers will do that. NeilBrown -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
