Re: [PATCH v2 6/7] quota: simplify drop_dquot_ref()

[Baokun Li]

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
.