Re: [RFC v6.5-rc2 3/3] fs: lockd: introduce safe async lock op

[Jeff Layton <jlayton@kernel.org>]

On Thu, 2023-07-20 at 08:58 -0400, Alexander Aring wrote:
> This patch reverts mostly commit 40595cdc93ed ("nfs: block notification
> on fs with its own ->lock") and introduces an EXPORT_OP_SAFE_ASYNC_LOCK
> export flag to signal that the "own ->lock" implementation supports
> async lock requests. The only main user is DLM that is used by GFS2 and
> OCFS2 filesystem. Those implement their own lock() implementation and
> return FILE_LOCK_DEFERRED as return value. Since commit 40595cdc93ed
> ("nfs: block notification on fs with its own ->lock") the DLM
> implementation were never updated. This patch should prepare for DLM
> to set the EXPORT_OP_SAFE_ASYNC_LOCK export flag and update the DLM
> plock implementation regarding to it.
>
> Signed-off-by: Alexander Aring <aahringo@redhat.com>
> ---
>  fs/lockd/svclock.c       |  5 ++---
>  fs/nfsd/nfs4state.c      | 11 ++++++++---
>  include/linux/exportfs.h |  1 +
>  3 files changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
> index 62ef27a69a9e..54a67bd33843 100644
> --- a/fs/lockd/svclock.c
> +++ b/fs/lockd/svclock.c
> @@ -483,9 +483,7 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
>  	    struct nlm_host *host, struct nlm_lock *lock, int wait,
>  	    struct nlm_cookie *cookie, int reclaim)
>  {
> -#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
>  	struct inode		*inode = nlmsvc_file_inode(file);
> -#endif
>  	struct nlm_block	*block = NULL;
>  	int			error;
>  	int			mode;
> @@ -499,7 +497,8 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
>  				(long long)lock->fl.fl_end,
>  				wait);
>  
> -	if (nlmsvc_file_file(file)->f_op->lock) {
> +	if (!(inode->i_sb->s_export_op->flags & EXPORT_OP_SAFE_ASYNC_LOCK) &&
> +	    nlmsvc_file_file(file)->f_op->lock) {
>  		async_block = wait;
>  		wait = 0;
>  	}
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 6e61fa3acaf1..efcea229d640 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -7432,6 +7432,7 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  	struct nfsd4_blocked_lock *nbl = NULL;
>  	struct file_lock *file_lock = NULL;
>  	struct file_lock *conflock = NULL;
> +	struct super_block *sb;
>  	__be32 status = 0;
>  	int lkflg;
>  	int err;
> @@ -7453,6 +7454,7 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  		dprintk("NFSD: nfsd4_lock: permission denied!\n");
>  		return status;
>  	}
> +	sb = cstate->current_fh.fh_dentry->d_sb;
>  
>  	if (lock->lk_is_new) {
>  		if (nfsd4_has_session(cstate))
> @@ -7504,7 +7506,8 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  	fp = lock_stp->st_stid.sc_file;
>  	switch (lock->lk_type) {
>  		case NFS4_READW_LT:
> -			if (nfsd4_has_session(cstate))
> +			if (sb->s_export_op->flags & EXPORT_OP_SAFE_ASYNC_LOCK &&

This will break existing filesystems that don't set the new flag. Maybe
you also need to test for the filesystem's ->lock operation here too?

This might be more nicely expressed in a helper function.

> +			    nfsd4_has_session(cstate))
>  				fl_flags |= FL_SLEEP;
>  			fallthrough;
>  		case NFS4_READ_LT:
> @@ -7516,7 +7519,8 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  			fl_type = F_RDLCK;
>  			break;
>  		case NFS4_WRITEW_LT:
> -			if (nfsd4_has_session(cstate))
> +			if (sb->s_export_op->flags & EXPORT_OP_SAFE_ASYNC_LOCK &&
> +			    nfsd4_has_session(cstate))
>  				fl_flags |= FL_SLEEP;
>  			fallthrough;
>  		case NFS4_WRITE_LT:
> @@ -7544,7 +7548,8 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>  	 * for file locks), so don't attempt blocking lock notifications
>  	 * on those filesystems:
>  	 */
> -	if (nf->nf_file->f_op->lock)
> +	if (!(sb->s_export_op->flags & EXPORT_OP_SAFE_ASYNC_LOCK) &&
> +	    nf->nf_file->f_op->lock)
>  		fl_flags &= ~FL_SLEEP;
>  
>  	nbl = find_or_allocate_block(lock_sop, &fp->fi_fhandle, nn);
> diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
> index 11fbd0ee1370..da742abbaf3e 100644
> --- a/include/linux/exportfs.h
> +++ b/include/linux/exportfs.h
> @@ -224,6 +224,7 @@ struct export_operations {
>  						  atomic attribute updates
>  						*/
>  #define EXPORT_OP_FLUSH_ON_CLOSE	(0x20) /* fs flushes file data on close */
> +#define EXPORT_OP_SAFE_ASYNC_LOCK	(0x40) /* fs can do async lock request */
>  	unsigned long	flags;
>  };
>  

-- 
Jeff Layton <jlayton@kernel.org>