Re: [RFCv2 6/7] dlm: use FL_SLEEP to check if blocking request

[Jeff Layton <jlayton@kernel.org>]

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@redhat.com>
> ---
>  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?


> +		} 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.
-- 
Jeff Layton <jlayton@kernel.org>