Messages in this thread | | | Subject | Re: [PATCH -next v2 8/9] block: fix null-pointer dereference in ioc_pd_init | From | Yu Kuai <> | Date | Thu, 1 Dec 2022 10:12:13 +0800 |
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Hi,
在 2022/12/01 4:50, Tejun Heo 写道: > On Wed, Nov 30, 2022 at 09:21:55PM +0800, Li Nan wrote: >> Remove block device when iocost is initializing may cause >> null-pointer dereference: >> >> CPU1 CPU2 >> ioc_qos_write >> blkcg_conf_open_bdev >> blkdev_get_no_open >> kobject_get_unless_zero >> blk_iocost_init >> rq_qos_add >> del_gendisk >> rq_qos_exit >> q->rq_qos = rqos->next >> //iocost is removed from q->roqs >> blkcg_activate_policy >> pd_init_fn >> ioc_pd_init >> ioc = q_to_ioc(blkg->q) >> //cant find iocost and return null >> >> Fix problem by moving rq_qos_exit() to disk_release(). ioc_qos_write() get >> bd_device.kobj in blkcg_conf_open_bdev(), so disk_release will not be >> actived until iocost initialization is complited. > > I think it'd be better to make del_gendisk wait for these in-flight > operations because this might fix the above particular issue but now all the > policies are exposed to request_queue in a state it never expected before. > > del_gendisk() is quiescing the queue around rq_qos_exit(), so maybe we can > piggyback on that and update blkcg_conf_open_bdev() to provide such > exclusion?
Let del_gendisk waiting for that sounds good, but I'm litter confused how to do that. Following are what I think about:
1) By mentioning that "del_gendisk() is quiescing the queue", do you suggest to add rcu_read_lock()? This seems wrong because blk_iocost_init requires memory allocation.
2) Hold gendisk open mutex
3) Use q_usage_counter, and in the meantime, rq_qos_add() and blkcg_activate_policy() will need refactoring to factor out freeze queue.
4) Define a new metux
Thanks, Kuai > > Thanks. >
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