[PATCH AUTOSEL for 4.9 156/190] dm: ensure bio submission follows a depth-first tree walk

From: NeilBrown [ Upstream commit 18a25da84354c6bb655320de6072c00eda6eb602 ] A dm device can, in general, represent a tree of targets, each of which handles a sub-range of the range of blocks handled by the parent. The bio sequencing managed by generic_make_request() requires

[PATCH AUTOSEL for 4.9 156/190] dm: ensure bio submission follows a depth-first tree walk

From: NeilBrown [ Upstream commit 18a25da84354c6bb655320de6072c00eda6eb602 ] A dm device can, in general, represent a tree of targets, each of which handles a sub-range of the range of blocks handled by the parent. The bio sequencing managed by generic_make_request() requires that bios are