md/raid10: handle merge_bvec_fn in member devices.

Currently we don't honour merge_bvec_fn in member devices so if there
is one, we force all requests to be single-page at most.
This is not ideal.

So enhance the raid10 merge_bvec_fn to check that function in children
as well.

This introduces a small problem.  There is no locking around calls
the ->merge_bvec_fn and subsequent calls to ->make_request.  So a
device added between these could end up getting a request which
violates its merge_bvec_fn.

Currently the best we can do is synchronize_sched().  This will work
providing no preemption happens.  If there is preemption, we just
have to hope that new devices are largely consistent with old devices.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 119de175bf12..4566b61373d5 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -5073,6 +5073,7 @@ static void md_clean(struct mddev *mddev)
         mddev->changed = 0;
         mddev->degraded = 0;
         mddev->safemode = 0;
+        mddev->merge_check_needed = 0;
         mddev->bitmap_info.offset = 0;
         mddev->bitmap_info.default_offset = 0;
         mddev->bitmap_info.chunksize = 0;