Messages in this thread | | | Date | Thu, 29 Jun 2023 22:16:08 +0800 | Subject | Re: [PATCH v2 6/7] quota: simplify drop_dquot_ref() | From | Baokun Li <> |
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On 2023/6/29 22:09, Jan Kara wrote: > On Thu 29-06-23 20:13:05, Baokun Li wrote: >> On 2023/6/29 19:08, Jan Kara wrote: >>> On Wed 28-06-23 21:21:54, Baokun Li wrote: >>>> Now when dqput() drops the last reference count, it will call >>>> synchronize_srcu(&dquot_srcu) in quota_release_workfn() to ensure that >>>> no other user will use the dquot after the last reference count is dropped, >>>> so we don't need to call synchronize_srcu(&dquot_srcu) in drop_dquot_ref() >>>> and remove the corresponding logic directly to simplify the code. >>> Nice simplification! It is also important that dqput() now cannot sleep >>> which was another reason for the logic with tofree_head in >>> remove_inode_dquot_ref(). >> I don't understand this sentence very well, so I would appreciate it >> >> if you could explain it in detail. 🤔 > OK, let me phrase it in a "changelog" way :): > > remove_inode_dquot_ref() currently does not release the last dquot > reference but instead adds the dquot to tofree_head list. This is because > dqput() can sleep while dropping of the last dquot reference (writing back > the dquot and calling ->release_dquot()) and that must not happen under > dq_list_lock. Now that dqput() queues the final dquot cleanup into a > workqueue, remove_inode_dquot_ref() can call dqput() unconditionally > and we can significantly simplify it. > > Honza I suddenly understand what you mean, you mean that now dqput() doesn't have any possible sleep operation. So it can be called in spin_lock at will.
I was confused because I understood that dqput() cannot be called in the context of possible sleep.
Thank you very much for the detailed explanation! Now there is only the problem in patch 5.
Thanks! -- With Best Regards, Baokun Li .
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