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

[Jan Kara <jack@suse.cz>]

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
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR