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Revert "blk-throttle: fix race between blkcg_bio_issue_check() and cgroup_rmdir()" 

This reverts commit 4c6994806f.

Destroying blkgs is tricky because of the nature of the relationship. A
blkg should go away when either a blkcg or a request_queue goes away.
However, blkg's pin the blkcg to ensure they remain valid. To break this
cycle, when a blkcg is offlined, blkgs put back their css ref. This
eventually lets css_free() get called which frees the blkcg.

The above commit (4c6994806f) breaks this order of events by trying to
destroy blkgs in css_free(). As the blkgs still hold references to the
blkcg, css_free() is never called.

The race between blkcg_bio_issue_check() and cgroup_rmdir() will be
addressed in the following patch by delaying destruction of a blkg until
all writeback associated with the blkcg has been finished.

Fixes: 4c6994806f ("blk-throttle: fix race between blkcg_bio_issue_check() and cgroup_rmdir()")
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Dennis Zhou <dennisszhou@gmail.com>
Cc: Jiufei Xue <jiufei.xue@linux.alibaba.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Dennis Zhou (Facebook) 2018-08-31 16:22:42 -04:00 committed by Jens Axboe
parent 52bd456a66
commit 6b06546206
2 changed files with 16 additions and 63 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

78
block/blk-cgroup.c
View File

@ -310,28 +310,11 @@ struct blkcg_gq *blkg_lookup_create(struct blkcg *blkcg,
}
}
static void blkg_pd_offline(struct blkcg_gq *blkg)
{
int i;
lockdep_assert_held(blkg->q->queue_lock);
lockdep_assert_held(&blkg->blkcg->lock);
for (i = 0; i < BLKCG_MAX_POLS; i++) {
struct blkcg_policy *pol = blkcg_policy[i];
if (blkg->pd[i] && !blkg->pd[i]->offline &&
pol->pd_offline_fn) {
pol->pd_offline_fn(blkg->pd[i]);
blkg->pd[i]->offline = true;
}
}
}
static void blkg_destroy(struct blkcg_gq *blkg)
{
struct blkcg *blkcg = blkg->blkcg;
struct blkcg_gq *parent = blkg->parent;
int i;
lockdep_assert_held(blkg->q->queue_lock);
lockdep_assert_held(&blkcg->lock);
@ -340,6 +323,13 @@ static void blkg_destroy(struct blkcg_gq *blkg)
WARN_ON_ONCE(list_empty(&blkg->q_node));
WARN_ON_ONCE(hlist_unhashed(&blkg->blkcg_node));
for (i = 0; i < BLKCG_MAX_POLS; i++) {
struct blkcg_policy *pol = blkcg_policy[i];
if (blkg->pd[i] && pol->pd_offline_fn)
pol->pd_offline_fn(blkg->pd[i]);
}
if (parent) {
blkg_rwstat_add_aux(&parent->stat_bytes, &blkg->stat_bytes);
blkg_rwstat_add_aux(&parent->stat_ios, &blkg->stat_ios);
@ -382,7 +372,6 @@ static void blkg_destroy_all(struct request_queue *q)
struct blkcg *blkcg = blkg->blkcg;
spin_lock(&blkcg->lock);
blkg_pd_offline(blkg);
blkg_destroy(blkg);
spin_unlock(&blkcg->lock);
}
@ -1058,25 +1047,25 @@ static struct cftype blkcg_legacy_files[] = {
* @css: css of interest
*
* This function is called when @css is about to go away and responsible
* for offlining all blkgs pd and killing all wbs associated with @css.
* blkgs pd offline should be done while holding both q and blkcg locks.
* As blkcg lock is nested inside q lock, this function performs reverse
* double lock dancing.
* for shooting down all blkgs associated with @css. blkgs should be
* removed while holding both q and blkcg locks. As blkcg lock is nested
* inside q lock, this function performs reverse double lock dancing.
*
* This is the blkcg counterpart of ioc_release_fn().
*/
static void blkcg_css_offline(struct cgroup_subsys_state *css)
{
struct blkcg *blkcg = css_to_blkcg(css);
struct blkcg_gq *blkg;
spin_lock_irq(&blkcg->lock);
hlist_for_each_entry(blkg, &blkcg->blkg_list, blkcg_node) {
while (!hlist_empty(&blkcg->blkg_list)) {
struct blkcg_gq *blkg = hlist_entry(blkcg->blkg_list.first,
struct blkcg_gq, blkcg_node);
struct request_queue *q = blkg->q;
if (spin_trylock(q->queue_lock)) {
blkg_pd_offline(blkg);
blkg_destroy(blkg);
spin_unlock(q->queue_lock);
} else {
spin_unlock_irq(&blkcg->lock);
@ -1090,43 +1079,11 @@ static void blkcg_css_offline(struct cgroup_subsys_state *css)
wb_blkcg_offline(blkcg);
}
/**
* blkcg_destroy_all_blkgs - destroy all blkgs associated with a blkcg
* @blkcg: blkcg of interest
*
* This function is called when blkcg css is about to free and responsible for
* destroying all blkgs associated with @blkcg.
* blkgs should be removed while holding both q and blkcg locks. As blkcg lock
* is nested inside q lock, this function performs reverse double lock dancing.
*/
static void blkcg_destroy_all_blkgs(struct blkcg *blkcg)
{
spin_lock_irq(&blkcg->lock);
while (!hlist_empty(&blkcg->blkg_list)) {
struct blkcg_gq *blkg = hlist_entry(blkcg->blkg_list.first,
struct blkcg_gq,
blkcg_node);
struct request_queue *q = blkg->q;
if (spin_trylock(q->queue_lock)) {
blkg_destroy(blkg);
spin_unlock(q->queue_lock);
} else {
spin_unlock_irq(&blkcg->lock);
cpu_relax();
spin_lock_irq(&blkcg->lock);
}
}
spin_unlock_irq(&blkcg->lock);
}
static void blkcg_css_free(struct cgroup_subsys_state *css)
{
struct blkcg *blkcg = css_to_blkcg(css);
int i;
blkcg_destroy_all_blkgs(blkcg);
mutex_lock(&blkcg_pol_mutex);
list_del(&blkcg->all_blkcgs_node);
@ -1480,11 +1437,8 @@ void blkcg_deactivate_policy(struct request_queue *q,
list_for_each_entry(blkg, &q->blkg_list, q_node) {
if (blkg->pd[pol->plid]) {
if (!blkg->pd[pol->plid]->offline &&
pol->pd_offline_fn) {
if (pol->pd_offline_fn)
pol->pd_offline_fn(blkg->pd[pol->plid]);
blkg->pd[pol->plid]->offline = true;
}
pol->pd_free_fn(blkg->pd[pol->plid]);
blkg->pd[pol->plid] = NULL;
}

1
include/linux/blk-cgroup.h
View File

@ -89,7 +89,6 @@ struct blkg_policy_data {
/* the blkg and policy id this per-policy data belongs to */
struct blkcg_gq *blkg;
int plid;
bool offline;
};
/*