Hi,
On Thu, Aug 17, 2023 at 7:27 AM Jeff Layton <jlayton@xxxxxxxxxx> wrote:
>
> On Wed, 2023-08-16 at 21:19 -0400, Alexander Aring wrote:
> > Hi,
> >
> > On Wed, Aug 16, 2023 at 9:07 AM Jeff Layton <jlayton@xxxxxxxxxx> wrote:
> > >
> > > On Mon, 2023-08-14 at 17:11 -0400, Alexander Aring wrote:
> > > > This patch uses the FL_SLEEP flag in struct file_lock to check if it's a
> > > > blocking request in case if the request coming from nfs lockd process
> > > > indicated by lm_grant() is set.
> > > >
> > > > IF FL_SLEEP is set a asynchronous blocking request is being made and
> > > > it's waiting for lm_grant() callback being called to signal the lock was
> > > > granted. If it's not set a synchronous non-blocking request is being made.
> > > >
> > > > Signed-off-by: Alexander Aring <aahringo@xxxxxxxxxx>
> > > > ---
> > > > fs/dlm/plock.c | 38 ++++++++++++++++++++++----------------
> > > > 1 file changed, 22 insertions(+), 16 deletions(-)
> > > >
> > > > diff --git a/fs/dlm/plock.c b/fs/dlm/plock.c
> > > > index 0094fa4004cc..524771002a2f 100644
> > > > --- a/fs/dlm/plock.c
> > > > +++ b/fs/dlm/plock.c
> > > > @@ -140,7 +140,6 @@ int dlm_posix_lock(dlm_lockspace_t *lockspace, u64 number, struct file *file,
> > > > op->info.optype = DLM_PLOCK_OP_LOCK;
> > > > op->info.pid = fl->fl_pid;
> > > > op->info.ex = (fl->fl_type == F_WRLCK);
> > > > - op->info.wait = IS_SETLKW(cmd);
> > > > op->info.fsid = ls->ls_global_id;
> > > > op->info.number = number;
> > > > op->info.start = fl->fl_start;
> > > > @@ -148,24 +147,31 @@ int dlm_posix_lock(dlm_lockspace_t *lockspace, u64 number, struct file *file,
> > > > op->info.owner = (__u64)(long)fl->fl_owner;
> > > > /* async handling */
> > > > if (fl->fl_lmops && fl->fl_lmops->lm_grant) {
> > > > - op_data = kzalloc(sizeof(*op_data), GFP_NOFS);
> > > > - if (!op_data) {
> > > > - dlm_release_plock_op(op);
> > > > - rv = -ENOMEM;
> > > > - goto out;
> > > > - }
> > > > + if (fl->fl_flags & FL_SLEEP) {
> > > > + op_data = kzalloc(sizeof(*op_data), GFP_NOFS);
> > > > + if (!op_data) {
> > > > + dlm_release_plock_op(op);
> > > > + rv = -ENOMEM;
> > > > + goto out;
> > > > + }
> > > >
> > > > - op_data->callback = fl->fl_lmops->lm_grant;
> > > > - locks_init_lock(&op_data->flc);
> > > > - locks_copy_lock(&op_data->flc, fl);
> > > > - op_data->fl = fl;
> > > > - op_data->file = file;
> > > > + op->info.wait = 1;
> > > > + op_data->callback = fl->fl_lmops->lm_grant;
> > > > + locks_init_lock(&op_data->flc);
> > > > + locks_copy_lock(&op_data->flc, fl);
> > > > + op_data->fl = fl;
> > > > + op_data->file = file;
> > > >
> > > > - op->data = op_data;
> > > > + op->data = op_data;
> > > >
> > > > - send_op(op);
> > > > - rv = FILE_LOCK_DEFERRED;
> > > > - goto out;
> > > > + send_op(op);
> > > > + rv = FILE_LOCK_DEFERRED;
> > > > + goto out;
> > >
> > > A question...we're returning FILE_LOCK_DEFERRED after the DLM request is
> > > sent. If it ends up being blocked, what happens? Does it do a lm_grant
> > > downcall with -EAGAIN or something as the result?
> > >
> >
> > no, when info->wait is set then it is a blocked lock request, which
> > means lm_grant() will be called when the lock request is granted.
> >
>
> Ok, that's probably problematic with the current code too. lockd will
> time out the block after 7s, so if the lock isn't granted in that time
> it'll give up on it.
>
that's why blocked lock requests (meaning F_SETLKW, FL_SLEEP is set)
need to use NLM_NEVER? It will never give up on it.
I thought NLM_TIMEOUT is just the polling frequency for doing a
blocked request by doing non-blocking requests. Means trylocks in a
loop with a polling frequency.
> > >
> > > > + } else {
> > > > + op->info.wait = 0;
> > > > + }
> > > > + } else {
> > > > + op->info.wait = IS_SETLKW(cmd);
> > > > }
> > > >
> > > > send_op(op);
> > >
> > > Looks reasonable overall.
> > >
> > > Now that I look, we have quite a number of places in the kernel that
> > > seem to check for F_SETLKW, when what they really want is to check
> > > FL_SLEEP.
> >
> > Yes, so far I understand FL_SLEEP is F_SETLKW when you get only
> > F_SETLK in case of fl->fl_lmops && fl->fl_lmops->lm_grant is true. It
> > is confusing but this is how it works... if it's not set we will get
> > F_SETLKW and this should imply FL_SLEEP is set.
> >
> >
>
> Yeah. Might be good to consider how to make this more consistent across
> the kernel.
ok. I will do some grep and try to find those places.
- Alex
