Re: [PATCH 03/13 V2] blk: make the bioset rescue_workqueue optional.

From: Ming Lei
Date: Tue May 02 2017 - 23:25:17 EST

On Wed, May 3, 2017 at 6:34 AM, NeilBrown <neilb@xxxxxxxx> wrote:
> From 09017acf74ec4df674b78ca66f0924187f10d8a4 Mon Sep 17 00:00:00 2001
> From: NeilBrown <neilb@xxxxxxxx>
> Date: Fri, 10 Mar 2017 13:59:50 +1100
> Subject: [PATCH] blk: make the bioset rescue_workqueue optional.
> This patch converts bioset_create() to not create a workqueue by
> default, so alloctions will never trigger punt_bios_to_rescuer(). It
> also introduces a new flag BIOSET_NEED_RESCUER() which tells
> bioset_create() to preserve the old behavior.
> All callers of bioset_create() that are inside block device drivers,
> are given the BIOSET_NEED_RESCUER().
> biosets used by filesystems or other top-level users do not
> need rescuing as the bio can never be queued behind other
> bios. This includes fs_bio_set, blkdev_dio_pool,
> btrfs_bioset, xfs_ioend_bioset, and one allocated by
> target_core_iblock.c.
> biosets used by md/raid do not need rescuing as
> their usage was recently audited and revised to never
> risk deadlock.
> It is hoped that most, if not all, of the remaining biosets
> can end up being the non-rescued version.
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Credit-to: Ming Lei <ming.lei@xxxxxxxxxx> (minor fixes)
> Signed-off-by: NeilBrown <neilb@xxxxxxxx>

Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx>