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authorTejun Heo <tj@kernel.org>2015-07-09 16:39:50 -0400
committerJens Axboe <axboe@fb.com>2015-07-09 14:41:11 -0600
commit06b285bd11257bccc5a1b85a835507e33656aff2 (patch)
tree3cebcfe5a71ab8c0dcc1d03511dcd76a17653b55 /include
parent7876f930d0e78addc6bbdbba0d6c196a0788d545 (diff)
downloadlinux-06b285bd11257bccc5a1b85a835507e33656aff2.tar.bz2
blkcg: fix blkcg_policy_data allocation bug
e48453c386f3 ("block, cgroup: implement policy-specific per-blkcg data") updated per-blkcg policy data to be dynamically allocated. When a policy is registered, its policy data aren't created. Instead, when the policy is activated on a queue, the policy data are allocated if there are blkg's (blkcg_gq's) which are attached to a given blkcg. This is buggy. Consider the following scenario. 1. A blkcg is created. No blkg's attached yet. 2. The policy is registered. No policy data is allocated. 3. The policy is activated on a queue. As the above blkcg doesn't have any blkg's, it won't allocate the matching blkcg_policy_data. 4. An IO is issued from the blkcg and blkg is created and the blkcg still doesn't have the matching policy data allocated. With cfq-iosched, this leads to an oops. It also doesn't free policy data on policy unregistration assuming that freeing of all policy data on blkcg destruction should take care of it; however, this also is incorrect. 1. A blkcg has policy data. 2. The policy gets unregistered but the policy data remains. 3. Another policy gets registered on the same slot. 4. Later, the new policy tries to allocate policy data on the previous blkcg but the slot is already occupied and gets skipped. The policy ends up operating on the policy data of the previous policy. There's no reason to manage blkcg_policy_data lazily. The reason we do lazy allocation of blkg's is that the number of all possible blkg's is the product of cgroups and block devices which can reach a surprising level. blkcg_policy_data is contrained by the number of cgroups and shouldn't be a problem. This patch makes blkcg_policy_data to be allocated for all existing blkcg's on policy registration and freed on unregistration and removes blkcg_policy_data handling from policy [de]activation paths. This makes that blkcg_policy_data are created and removed with the policy they belong to and fixes the above described problems. Signed-off-by: Tejun Heo <tj@kernel.org> Fixes: e48453c386f3 ("block, cgroup: implement policy-specific per-blkcg data") Cc: Vivek Goyal <vgoyal@redhat.com> Cc: Arianna Avanzini <avanzini.arianna@gmail.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'include')
-rw-r--r--include/linux/blk-cgroup.h10
1 files changed, 2 insertions, 8 deletions
diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
index cf3e7bc22ef3..1b62d768c7df 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -89,18 +89,12 @@ struct blkg_policy_data {
* Policies that need to keep per-blkcg data which is independent
* from any request_queue associated to it must specify its size
* with the cpd_size field of the blkcg_policy structure and
- * embed a blkcg_policy_data in it. blkcg core allocates
- * policy-specific per-blkcg structures lazily the first time
- * they are actually needed, so it handles them together with
- * blkgs. cpd_init() is invoked to let each policy handle
- * per-blkcg data.
+ * embed a blkcg_policy_data in it. cpd_init() is invoked to let
+ * each policy handle per-blkcg data.
*/
struct blkcg_policy_data {
/* the policy id this per-policy data belongs to */
int plid;
-
- /* used during policy activation */
- struct list_head alloc_node;
};
/* association between a blk cgroup and a request queue */