md/raid10: call wait_barrier() for each request submitted.
md/raid10: call wait_barrier() for each request submitted.

wait_barrier() includes a counter, so we must call it precisely once
(unless balanced by allow_barrier()) for each request submitted.

Since
commit 20d0189b1012a37d2533a87fb451f7852f2418d1
    block: Introduce new bio_split()
in 3.14-rc1, we don't call it for the extra requests generated when
we need to split a bio.

When this happens the counter goes negative, any resync/recovery will
never start, and  "mdadm --stop" will hang.

Reported-by: Chris Murphy <da2ea5bee82302925a2874f529684e980c179d70@colorremedies.com>
Fixes: 20d0189b1012a37d2533a87fb451f7852f2418d1
Cc: 4fbacc2fa0ffdbb11bf1ad6925b886ebd08dd15f@vger.kernel.org (3.14+)
Cc: Kent Overstreet <99dffa8a9668ab7f6cde1c94b42a210109971113@daterainc.com>
Signed-off-by: NeilBrown <1c00aa603bb92d594c03cff60ecf8e63b2a5bcb1@suse.de>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs