New subject: [PATCH 5.15/5.10 2/2] blk-iocost: do not WARN if iocg was already offlined

17 Apr 2025

From: Yu Kuai yukuai3@huawei.com
[ Upstream commit dfd6200a095440b663099d8d42f1efb0175a1ce3 ]
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
Signed-off-by: Bin Lan bin.lan.cn@windriver.com
Signed-off-by: He Zhe zhe.he@windriver.com
---
Build test passed.
---
 block/blk-cgroup.c         | 24 +++++++++++++++++-------
 include/linux/blk-cgroup.h |  1 +
 2 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 6180c680136b..e372a3fc264e 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -192,6 +192,7 @@ static struct blkcg_gq *blkg_alloc(struct blkcg *blkcg, struct request_queue *q,
    	blkg->pd[i] = pd;
    	pd->blkg = blkg;
    	pd->plid = i;
+		pd->online = false;
    }
return blkg;
@@ -289,8 +290,11 @@ static struct blkcg_gq *blkg_create(struct blkcg *blkcg,
    	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;
@@ -390,8 +394,11 @@ 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;
@@ -1367,6 +1374,7 @@ 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 */
@@ -1374,9 +1382,11 @@ 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;
@@ -1438,7 +1448,7 @@ 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;
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index 27c363f6b281..c5eda86e4118 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -92,6 +92,7 @@ struct blkg_policy_data {
    /* the blkg and policy id this per-policy data belongs to */
    struct blkcg_gq			*blkg;
    int				plid;
+	bool				online;
 };
/*
-- 
2.34.1



    

[PATCH 5.15/5.10 1/2] blk-cgroup: support to track if policy is online