Re: [PATCH RFC 1/3] fs/lock: add new callback, lm_expire_lock, to lock_manager_operations

[dai.ngo@xxxxxxxxxx]

On 2/3/22 2:50 PM, Jeff Layton wrote:
> On Fri, 2022-01-28 at 11:39 -0800, Dai Ngo wrote:
> > Add new callback, lm_expire_lock, to lock_manager_operations to allow
> > the lock manager to take appropriate action to resolve the lock conflict
> > if possible. The callback takes 1 argument, the file_lock of the blocker
> > and returns true if the conflict was resolved else returns false. Note
> > that the lock manager has to be able to resolve the conflict while
> > the spinlock flc_lock is held.
> >
> > Lock manager, such as NFSv4 courteous server, uses this callback to
> > resolve conflict by destroying lock owner, or the NFSv4 courtesy client
> > (client that has expired but allowed to maintains its states) that owns
> > the lock.
> >
> > Signed-off-by: Dai Ngo <dai.ngo@xxxxxxxxxx>
> > ---
> >   Documentation/filesystems/locking.rst |  2 ++
> >   fs/locks.c                            | 14 ++++++++++----
> >   include/linux/fs.h                    |  1 +
> >   3 files changed, 13 insertions(+), 4 deletions(-)
> >
> > diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
> > index d36fe79167b3..57ce0fbc8ab1 100644
> > --- a/Documentation/filesystems/locking.rst
> > +++ b/Documentation/filesystems/locking.rst
> > @@ -439,6 +439,7 @@ prototypes::
> >   	void (*lm_break)(struct file_lock *); /* break_lease callback */
> >   	int (*lm_change)(struct file_lock **, int);
> >   	bool (*lm_breaker_owns_lease)(struct file_lock *);
> > +	bool (*lm_lock_conflict)(struct file_lock *);
> >   
> >   locking rules:
> >   
> > @@ -450,6 +451,7 @@ lm_grant:		no		no			no
> >   lm_break:		yes		no			no
> >   lm_change		yes		no			no
> >   lm_breaker_owns_lease:	no		no			no
> > +lm_lock_conflict:       no		no			no
> >   ======================	=============	=================	=========
> >   
> >   buffer_head
> > diff --git a/fs/locks.c b/fs/locks.c
> > index 0fca9d680978..052b42cc7f25 100644
> > --- a/fs/locks.c
> > +++ b/fs/locks.c
> > @@ -853,10 +853,13 @@ posix_test_lock(struct file *filp, struct file_lock *fl)
> >   
> >   	spin_lock(&ctx->flc_lock);
> >   	list_for_each_entry(cfl, &ctx->flc_posix, fl_list) {
> > -		if (posix_locks_conflict(fl, cfl)) {
> > -			locks_copy_conflock(fl, cfl);
> > -			goto out;
> > -		}
> > +		if (!posix_locks_conflict(fl, cfl))
> > +			continue;
> > +		if (cfl->fl_lmops && cfl->fl_lmops->lm_lock_conflict &&
> > +			!cfl->fl_lmops->lm_lock_conflict(cfl))
> > +			continue;
> > +		locks_copy_conflock(fl, cfl);
> > +		goto out;
> >   	}
> >   	fl->fl_type = F_UNLCK;
> >   out:
> > @@ -1059,6 +1062,9 @@ static int posix_lock_inode(struct inode *inode, struct file_lock *request,
> >   		list_for_each_entry(fl, &ctx->flc_posix, fl_list) {
> >   			if (!posix_locks_conflict(request, fl))
> >   				continue;
> > +			if (fl->fl_lmops && fl->fl_lmops->lm_lock_conflict &&
> > +				!fl->fl_lmops->lm_lock_conflict(fl))
> > +				continue;
> The naming of this op is a little misleading. We already know that there
> is a lock confict in this case. The question is whether it's resolvable
> by expiring a tardy client. That said, I don't have a better name to
> suggest at the moment.

I will leave it as is for now.

> A comment about what this function actually tells us would be nice here.

will do in v11.

Thanks,
-Dai

> >   			if (conflock)
> >   				locks_copy_conflock(conflock, fl);
> >   			error = -EAGAIN;
> > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > index bbf812ce89a8..21cb7afe2d63 100644
> > --- a/include/linux/fs.h
> > +++ b/include/linux/fs.h
> > @@ -1068,6 +1068,7 @@ struct lock_manager_operations {
> >   	int (*lm_change)(struct file_lock *, int, struct list_head *);
> >   	void (*lm_setup)(struct file_lock *, void **);
> >   	bool (*lm_breaker_owns_lease)(struct file_lock *);
> > +	bool (*lm_lock_conflict)(struct file_lock *cfl);
> >   };
> >   
> >   struct lock_manager {
> Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>