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blk-cgroup: support to track if policy is online

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A new field 'online' is added to blkg_policy_data to fix following
2 problem:

1) In blkcg_activate_policy(), if pd_alloc_fn() with 'GFP_NOWAIT'
   failed, 'queue_lock' will be dropped and pd_alloc_fn() will try again
   without 'GFP_NOWAIT'. In the meantime, remove cgroup can race with
   it, and pd_offline_fn() will be called without pd_init_fn() and
   pd_online_fn(). This way null-ptr-deference can be triggered.

2) In order to synchronize pd_free_fn() from blkg_free_workfn() and
   blkcg_deactivate_policy(), 'list_del_init(&blkg->q_node)' will be
   delayed to blkg_free_workfn(), hence pd_offline_fn() can be called
   first in blkg_destroy(), and then blkcg_deactivate_policy() will
   call it again, we must prevent it.

The new field 'online' will be set after pd_online_fn() and will be
cleared after pd_offline_fn(), in the meantime pd_offline_fn() will only
be called if 'online' is set.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230119110350.2287325-3-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Yu Kuai 2023-01-19 19:03:49 +08:00 committed by Jens Axboe
parent c7241babf0
commit dfd6200a09
2 changed files with 18 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
block/blk-cgroup.c
View File

@ -288,6 +288,7 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct gendisk *disk,
blkg->pd[i] = pd;
pd->blkg = blkg;
pd->plid = i;
pd->online = false;
}
return blkg;
@ -359,8 +360,11 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg, struct gendisk *disk,
for (i = 0; i < BLKCG_MAX_POLS; i++) {
struct blkcg_policy *pol = blkcg_policy[i];
if (blkg->pd[i] && pol->pd_online_fn)
pol->pd_online_fn(blkg->pd[i]);
if (blkg->pd[i]) {
if (pol->pd_online_fn)
pol->pd_online_fn(blkg->pd[i]);
blkg->pd[i]->online = true;
}
}
}
blkg->online = true;
@ -465,8 +469,11 @@ static void blkg_destroy(struct blkcg_gq *blkg)
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 (blkg->pd[i] && blkg->pd[i]->online) {
if (pol->pd_offline_fn)
pol->pd_offline_fn(blkg->pd[i]);
blkg->pd[i]->online = false;
}
}
blkg->online = false;
@ -1448,6 +1455,7 @@ int blkcg_activate_policy(struct request_queue *q,
blkg->pd[pol->plid] = pd;
pd->blkg = blkg;
pd->plid = pol->plid;
pd->online = false;
}
/* all allocated, init in the same order */
@ -1455,9 +1463,11 @@ int blkcg_activate_policy(struct request_queue *q,
list_for_each_entry_reverse(blkg, &q->blkg_list, q_node)
pol->pd_init_fn(blkg->pd[pol->plid]);
if (pol->pd_online_fn)
list_for_each_entry_reverse(blkg, &q->blkg_list, q_node)
list_for_each_entry_reverse(blkg, &q->blkg_list, q_node) {
if (pol->pd_online_fn)
pol->pd_online_fn(blkg->pd[pol->plid]);
blkg->pd[pol->plid]->online = true;
}
__set_bit(pol->plid, q->blkcg_pols);
ret = 0;
@ -1519,7 +1529,7 @@ void blkcg_deactivate_policy(struct request_queue *q,
spin_lock(&blkcg->lock);
if (blkg->pd[pol->plid]) {
if (pol->pd_offline_fn)
if (blkg->pd[pol->plid]->online && pol->pd_offline_fn)
pol->pd_offline_fn(blkg->pd[pol->plid]);
pol->pd_free_fn(blkg->pd[pol->plid]);
blkg->pd[pol->plid] = NULL;

1
block/blk-cgroup.h
View File

@ -135,6 +135,7 @@ struct blkg_policy_data {
/* the blkg and policy id this per-policy data belongs to */
struct blkcg_gq *blkg;
int plid;
bool online;
};
/*