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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)
tree2ffd5885a12acb44d90d3c3c1a578387bad94a32 /block/blk-cgroup.c
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>
Diffstat (limited to 'block/blk-cgroup.c')
-rw-r--r--block/blk-cgroup.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index f0605ab2a76..471fdcc5df8 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)
}
EXPORT_SYMBOL_GPL(cgroup_to_blkio_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);
+}
+EXPORT_SYMBOL_GPL(task_blkio_cgroup);
+
static inline void
blkio_update_group_weight(struct blkio_group *blkg, unsigned int weight)
{