Re: [PATCH 02/27] quota: Do more fine-grained locking in dquot_acquire()

[Jan Kara <jack@suse.cz>]

On Wed 16-08-17 10:35:48, Andreas Dilger wrote:
> On Aug 16, 2017, at 9:41 AM, Jan Kara <jack@suse.cz> wrote:
> > 
> > We need dqio_sem held just for reading when calling ->read_dqblk() in
> > dquot_acquire(). Also dqio_sem is not needed when manipulating dquot
> > flags (those are protected by dq_lock)
> 
> Nothing against the patch itself, but this comment is a bit confusing.
> 
> It would be good to list this dq_lock dependency at the dq_flags declaration.
> Looking through the code that accesses dq_flags, I see dquot_mark_dquot_dirty(),
> clear_dquot_dirty(), dquot_commit(), dqput() depend on dq_list_lock, but
> I don't see many of the users besides dquot_acquire() and dquot_release()
> getting dq_lock, only using the atomic bit operations on dq_flags.

Updated changelog to:

We need dqio_sem held just for reading when calling ->read_dqblk() in
dquot_acquire(). Also dqio_sem is not needed when setting DQ_READ_B and 
DQ_ACTIVE_B as concurrent reads and dquot activation are serialized by
dq_lock. So acquire and release dqio_sem closer to the place where it is
needed. This reduces lock hold time and will make locking changes
easier.

								Honza

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