From: "Dennis Zhou (Facebook)" dennisszhou@gmail.com
[ Upstream commit 6b06546206868f723f2061d703a3c3c378dcbf4c ]
This reverts commit 4c6994806f708559c2812b73501406e21ae5dcd0.
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 (4c6994806f70) 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: 4c6994806f70 ("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 Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- block/blk-cgroup.c | 78 ++++++++------------------------------ include/linux/blk-cgroup.h | 1 - 2 files changed, 16 insertions(+), 63 deletions(-)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index eb85cb87c40f..ec868373b11b 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -307,28 +307,11 @@ 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); @@ -337,6 +320,13 @@ 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); @@ -379,7 +369,6 @@ 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); } @@ -1006,54 +995,21 @@ 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) { - struct request_queue *q = blkg->q; - - if (spin_trylock(q->queue_lock)) { - blkg_pd_offline(blkg); - spin_unlock(q->queue_lock); - } else { - spin_unlock_irq(&blkcg->lock); - cpu_relax(); - spin_lock_irq(&blkcg->lock); - } - } - - spin_unlock_irq(&blkcg->lock); - - 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 blkcg_gq, blkcg_node); struct request_queue *q = blkg->q;
if (spin_trylock(q->queue_lock)) { @@ -1065,7 +1021,10 @@ static void blkcg_destroy_all_blkgs(struct blkcg *blkcg) spin_lock_irq(&blkcg->lock); } } + spin_unlock_irq(&blkcg->lock); + + wb_blkcg_offline(blkcg); }
static void blkcg_css_free(struct cgroup_subsys_state *css) @@ -1073,8 +1032,6 @@ 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); @@ -1412,11 +1369,8 @@ 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; } diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h index 0fce47d5acb1..5d46b83d4820 100644 --- a/include/linux/blk-cgroup.h +++ b/include/linux/blk-cgroup.h @@ -88,7 +88,6 @@ struct blkg_policy_data { /* the blkg and policy id this per-policy data belongs to */ struct blkcg_gq *blkg; int plid; - bool offline; };
/*