From: NeilBrown <neilb@suse.de>
Date: Mon, 19 Mar 2012 01:46:39 +0000 (+1100)
Subject: md/raid10: handle merge_bvec_fn in member devices.
X-Git-Tag: v3.4-rc1~147^2~10
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=050b66152f87c79e8d66aed0e7996f9336462d5f;p=pandora-kernel.git

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>
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