On Mon, Dec 06, 2021 at 07:52:29PM +0000, Trond Myklebust wrote:
> On Mon, 2021-12-06 at 18:39 +0000, Chuck Lever III wrote:
> >
> >
> > > On Dec 6, 2021, at 12:59 PM, Dai Ngo <dai.ngo@xxxxxxxxxx> 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 2 arguments, file_lock of the
> > > blocker
> > > and a testonly flag:
> > >
> > > testonly = 1 check and return true if lock conflict can be
> > > resolved
> > > else return false.
> > > testonly = 0 resolve the conflict if possible, return true if
> > > conflict
> > > was resolved esle return false.
> > >
> > > 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>
> >
> > Al, Jeff, as co-maintainers of record for fs/locks.c, can you give
> > an Ack or Reviewed-by? I'd like to take this patch through the nfsd
> > tree for v5.17. Thanks for your time!
> >
> >
> > > ---
> > > fs/locks.c | 28 +++++++++++++++++++++++++---
> > > include/linux/fs.h | 1 +
> > > 2 files changed, 26 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/fs/locks.c b/fs/locks.c
> > > index 3d6fb4ae847b..0fef0a6322c7 100644
> > > --- a/fs/locks.c
> > > +++ b/fs/locks.c
> > > @@ -954,6 +954,7 @@ posix_test_lock(struct file *filp, struct
> > > file_lock *fl)
> > > struct file_lock *cfl;
> > > struct file_lock_context *ctx;
> > > struct inode *inode = locks_inode(filp);
> > > + bool ret;
> > >
> > > ctx = smp_load_acquire(&inode->i_flctx);
> > > if (!ctx || list_empty_careful(&ctx->flc_posix)) {
> > > @@ -962,11 +963,20 @@ posix_test_lock(struct file *filp, struct
> > > file_lock *fl)
> > > }
> > >
> > > spin_lock(&ctx->flc_lock);
> > > +retry:
> > > 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_expire_lock
> > > &&
> > > + cfl->fl_lmops->lm_expire_lock(cfl,
> > > 1)) {
> > > + spin_unlock(&ctx->flc_lock);
> > > + ret = cfl->fl_lmops->lm_expire_lock(cfl,
> > > 0);
> > > + spin_lock(&ctx->flc_lock);
> > > + if (ret)
> > > + goto retry;
> > > }
> > > + locks_copy_conflock(fl, cfl);
>
> How do you know 'cfl' still points to a valid object after you've
> dropped the spin lock that was protecting the list?
Ugh, good point, I should have noticed that when I suggested this
approach....
Maybe the first call could instead return return some reference-counted
object that a second call could wait on.
Better, maybe it could add itself to a list of such things and then we
could do this in one pass.
--b.
>
> > > + goto out;
> > > }
> > > fl->fl_type = F_UNLCK;
> > > out:
> > > @@ -1140,6 +1150,7 @@ static int posix_lock_inode(struct inode
> > > *inode, struct file_lock *request,
> > > int error;
> > > bool added = false;
> > > LIST_HEAD(dispose);
> > > + bool ret;
> > >
> > > ctx = locks_get_lock_context(inode, request->fl_type);
> > > if (!ctx)
> > > @@ -1166,9 +1177,20 @@ static int posix_lock_inode(struct inode
> > > *inode, struct file_lock *request,
> > > * blocker's list of waiters and the global blocked_hash.
> > > */
> > > if (request->fl_type != F_UNLCK) {
> > > +retry:
> > > 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_expire_lock &&
> > > + fl->fl_lmops-
> > > >lm_expire_lock(fl, 1)) {
> > > + spin_unlock(&ctx->flc_lock);
> > > + percpu_up_read(&file_rwsem);
> > > + ret = fl->fl_lmops-
> > > >lm_expire_lock(fl, 0);
> > > + percpu_down_read(&file_rwsem);
> > > + spin_lock(&ctx->flc_lock);
> > > + if (ret)
> > > + goto retry;
> > > + }
>
> ditto.
>
> > > if (conflock)
> > > locks_copy_conflock(conflock, fl);
> > > error = -EAGAIN;
> > > diff --git a/include/linux/fs.h b/include/linux/fs.h
> > > index e7a633353fd2..1a76b6451398 100644
> > > --- a/include/linux/fs.h
> > > +++ b/include/linux/fs.h
> > > @@ -1071,6 +1071,7 @@ 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_expire_lock)(struct file_lock *fl, bool
> > > testonly);
> > > };
> > >
> > > struct lock_manager {
> > > --
> > > 2.9.5
> > >
> >
> > --
> > Chuck Lever
> >
> >
> >
>
> --
> Trond Myklebust
> Linux NFS client maintainer, Hammerspace
> trond.myklebust@xxxxxxxxxxxxxxx
>
>
