diff options
authorVivek Goyal <vgoyal@redhat.com>2011-05-16 15:24:08 +0200
committerJens Axboe <jaxboe@fusionio.com>2011-05-16 15:24:08 +0200
commit70087dc38cc77ca8f46059564c00338777734762 (patch)
parent02e352287a40bd456eb78df705bf888bc3161d3f (diff)
blk-throttle: Use task_subsys_state() to determine a task's blkio_cgroup
Currentlly we first map the task to cgroup and then cgroup to blkio_cgroup. There is a more direct way to get to blkio_cgroup from task using task_subsys_state(). Use that. The real reason for the fix is that it also avoids a race in generic cgroup code. During remount/umount rebind_subsystems() is called and it can do following with and rcu protection. cgrp->subsys[i] = NULL; That means if somebody got hold of cgroup under rcu and then it tried to do cgroup->subsys[] to get to blkio_cgroup, it would get NULL which is wrong. I was running into this race condition with ltp running on a upstream derived kernel and that lead to crash. So ideally we should also fix cgroup generic code to wait for rcu grace period before setting pointer to NULL. Li Zefan is not very keen on introducing synchronize_wait() as he thinks it will slow down moun/remount/umount operations. So for the time being atleast fix the kernel crash by taking a more direct route to blkio_cgroup. One tester had reported a crash while running LTP on a derived kernel and with this fix crash is no more seen while the test has been running for over 6 days. Signed-off-by: Vivek Goyal <vgoyal@redhat.com> Reviewed-by: Li Zefan <lizf@cn.fujitsu.com> Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
4 files changed, 19 insertions, 11 deletions
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index f0605ab2a761..471fdcc5df85 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -114,6 +114,13 @@ struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup)
+struct blkio_cgroup *task_blkio_cgroup(struct task_struct *tsk)
+ return container_of(task_subsys_state(tsk, blkio_subsys_id),
+ struct blkio_cgroup, css);
static inline void
blkio_update_group_weight(struct blkio_group *blkg, unsigned int weight)
diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
index 10919fae2d3a..c774930cc206 100644
--- a/block/blk-cgroup.h
+++ b/block/blk-cgroup.h
@@ -291,6 +291,7 @@ static inline void blkiocg_set_start_empty_time(struct blkio_group *blkg) {}
extern struct blkio_cgroup blkio_root_cgroup;
extern struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup);
+extern struct blkio_cgroup *task_blkio_cgroup(struct task_struct *tsk);
extern void blkiocg_add_blkio_group(struct blkio_cgroup *blkcg,
struct blkio_group *blkg, void *key, dev_t dev,
enum blkio_policy_id plid);
@@ -314,6 +315,8 @@ void blkiocg_update_io_remove_stats(struct blkio_group *blkg,
struct cgroup;
static inline struct blkio_cgroup *
cgroup_to_blkio_cgroup(struct cgroup *cgroup) { return NULL; }
+static inline struct blkio_cgroup *
+task_blkio_cgroup(struct task_struct *tsk) { return NULL; }
static inline void blkiocg_add_blkio_group(struct blkio_cgroup *blkcg,
struct blkio_group *blkg, void *key, dev_t dev,
diff --git a/block/blk-throttle.c b/block/blk-throttle.c
index 0475a22a420d..252a81a306f7 100644
--- a/block/blk-throttle.c
+++ b/block/blk-throttle.c
@@ -160,9 +160,8 @@ static void throtl_put_tg(struct throtl_grp *tg)
static struct throtl_grp * throtl_find_alloc_tg(struct throtl_data *td,
- struct cgroup *cgroup)
+ struct blkio_cgroup *blkcg)
- struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
struct throtl_grp *tg = NULL;
void *key = td;
struct backing_dev_info *bdi = &td->queue->backing_dev_info;
@@ -229,12 +228,12 @@ done:
static struct throtl_grp * throtl_get_tg(struct throtl_data *td)
- struct cgroup *cgroup;
struct throtl_grp *tg = NULL;
+ struct blkio_cgroup *blkcg;
- cgroup = task_cgroup(current, blkio_subsys_id);
- tg = throtl_find_alloc_tg(td, cgroup);
+ blkcg = task_blkio_cgroup(current);
+ tg = throtl_find_alloc_tg(td, blkcg);
if (!tg)
tg = &td->root_tg;
diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index 5b52011e3a40..ab7a9e6a9b1c 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1014,10 +1014,9 @@ void cfq_update_blkio_group_weight(void *key, struct blkio_group *blkg,
cfqg->needs_update = true;
-static struct cfq_group *
-cfq_find_alloc_cfqg(struct cfq_data *cfqd, struct cgroup *cgroup, int create)
+static struct cfq_group * cfq_find_alloc_cfqg(struct cfq_data *cfqd,
+ struct blkio_cgroup *blkcg, int create)
- struct blkio_cgroup *blkcg = cgroup_to_blkio_cgroup(cgroup);
struct cfq_group *cfqg = NULL;
void *key = cfqd;
int i, j;
@@ -1079,12 +1078,12 @@ done:
static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd, int create)
- struct cgroup *cgroup;
+ struct blkio_cgroup *blkcg;
struct cfq_group *cfqg = NULL;
- cgroup = task_cgroup(current, blkio_subsys_id);
- cfqg = cfq_find_alloc_cfqg(cfqd, cgroup, create);
+ blkcg = task_blkio_cgroup(current);
+ cfqg = cfq_find_alloc_cfqg(cfqd, blkcg, create);
if (!cfqg && create)
cfqg = &cfqd->root_group;