Commit 4308a434 authored by Tejun Heo's avatar Tejun Heo Committed by Jens Axboe
Browse files

blkcg: don't offline parent blkcg first 



blkcg->cgwb_refcnt is used to delay blkcg offlining so that blkgs
don't get offlined while there are active cgwbs on them.  However, it
ends up making offlining unordered sometimes causing parents to be
offlined before children.

Let's fix this by making child blkcgs pin the parents' online states.

Note that pin/unpin names are chosen over get/put intentionally
because css uses get/put online for something different.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent d866dbf6

block/blk-cgroup.c

+16 −0
Original line number Diff line number Diff line
@@ -1006,6 +1006,21 @@ unlock: 
	return ret;

}



static int blkcg_css_online(struct cgroup_subsys_state *css)

{

	struct blkcg *blkcg = css_to_blkcg(css);

	struct blkcg *parent = blkcg_parent(blkcg);



	/*

	 * blkcg_pin_online() is used to delay blkcg offline so that blkgs

	 * don't go offline while cgwbs are still active on them.  Pin the

	 * parent so that offline always happens towards the root.

	 */

	if (parent)

		blkcg_pin_online(parent);

	return 0;

}



/**

 * blkcg_init_queue - initialize blkcg part of request queue

 * @q: request_queue to initialize
@@ -1199,6 +1214,7 @@ static void blkcg_exit(struct task_struct *tsk) 


struct cgroup_subsys io_cgrp_subsys = {

	.css_alloc = blkcg_css_alloc,

	.css_online = blkcg_css_online,

	.css_offline = blkcg_css_offline,

	.css_free = blkcg_css_free,

	.can_attach = blkcg_can_attach,

include/linux/blk-cgroup.h

+5 −1
Original line number Diff line number Diff line
@@ -436,8 +436,12 @@ static inline void blkcg_pin_online(struct blkcg *blkcg) 
 */

static inline void blkcg_unpin_online(struct blkcg *blkcg)

{

	if (refcount_dec_and_test(&blkcg->online_pin))

	do {

		if (!refcount_dec_and_test(&blkcg->online_pin))

			break;

		blkcg_destroy_blkgs(blkcg);

		blkcg = blkcg_parent(blkcg);

	} while (blkcg);

}



/**

CRA Git | Maintained and supported by SUSTech CRA and CCSE