Messages in this thread | | | Subject | Re: [PATCH -next 0/4] blk-cgroup: synchronize del_gendisk() with configuring cgroup policy | From | Yu Kuai <> | Date | Wed, 21 Dec 2022 09:10:33 +0800 |
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Hi,
在 2022/12/21 0:01, Tejun Heo 写道: > Hello, > > On Tue, Dec 20, 2022 at 05:19:12PM +0800, Yu Kuai wrote: >> Yes, that sounds good. BTW, queue_lock is also used to protect >> pd_alloc_fn/pd_init_fn,and we found that blkcg_activate_policy() is >> problematic: >> >> blkcg_activate_policy >> spin_lock_irq(&q->queue_lock); >> list_for_each_entry_reverse(blkg, &q->blkg_list >> pd_alloc_fn(GFP_NOWAIT | __GFP_NOWARN,...) -> failed >> >> spin_unlock_irq(&q->queue_lock); >> // release queue_lock here is problematic, this will cause >> pd_offline_fn called without pd_init_fn. >> pd_alloc_fn(__GFP_NOWARN,...) > > So, if a blkg is destroyed while a policy is being activated, right? Yes, remove cgroup can race with this, for bfq null pointer deference will be triggered in bfq_pd_offline().
> >> If we are using a mutex to protect rq_qos ops, it seems the right thing >> to do do also using the mutex to protect blkcg_policy ops, and this >> problem can be fixed because mutex can be held to alloc memroy with >> GFP_KERNEL. What do you think? > > One worry is that switching to mutex can be more headache due to destroy > path synchronization. Another approach would be using a per-blkg flag to > track whether a blkg has been initialized. I think perhaps you mean per blkg_policy_data flag? per blkg flag should not work in this case.
Thanks, Kuai > > Thanks. >
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