Re: [PATCH 3/3] nfs: don't allow reexport reclaims

[Trond Myklebust <trondmy@hammerspace.com>]

On Mon, 2021-06-14 at 10:48 -0400, J. Bruce Fields wrote:
> From: "J. Bruce Fields" <bfields@redhat.com>
> 
> In the reexport case, nfsd is currently passing along locks with the
> reclaim bit set.  The client sends a new lock request, which is
> granted
> if there's currently no conflict--even if it's possible a conflicting
> lock could have been briefly held in the interim.
> 
> We don't currently have any way to safely grant reclaim, so for now
> let's just deny them all.
> 
> I'm doing this by passing the reclaim bit to nfs and letting it fail
> the
> call, with the idea that eventually the client might be able to do
> something more forgiving here.
> 
> Signed-off-by: J. Bruce Fields <bfields@redhat.com>
> ---
>  fs/nfs/file.c       | 3 +++
>  fs/nfsd/nfs4state.c | 3 +++
>  fs/nfsd/nfsproc.c   | 1 +
>  include/linux/fs.h  | 1 +
>  4 files changed, 8 insertions(+)
> 
> diff --git a/fs/nfs/file.c b/fs/nfs/file.c
> index 1fef107961bc..35a29b440e3e 100644
> --- a/fs/nfs/file.c
> +++ b/fs/nfs/file.c
> @@ -806,6 +806,9 @@ int nfs_lock(struct file *filp, int cmd, struct
> file_lock *fl)
>  
>         nfs_inc_stats(inode, NFSIOS_VFSLOCK);
>  
> +       if (fl->fl_flags & FL_RECLAIM)
> +               return -NFSERR_NO_GRACE;

NACK. nfs_lock() is required to return a POSIX error. I know that right
now, nfsd is the only thing setting FL_RECLAIM, but we can't guarantee
that will always be the case.

> +
>         /* No mandatory locks over NFS */
>         if (__mandatory_lock(inode) && fl->fl_type != F_UNLCK)
>                 goto out_err;
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 00d98bbab2a6..3ef42c0d5d38 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -6903,6 +6903,9 @@ nfsd4_lock(struct svc_rqst *rqstp, struct
> nfsd4_compound_state *cstate,
>         if (!locks_in_grace(net) && lock->lk_reclaim)
>                 goto out;
>  
> +       if (lock->lk_reclaim)
> +               fl_flags |= FL_RECLAIM;
> +
>         fp = lock_stp->st_stid.sc_file;
>         switch (lock->lk_type) {
>                 case NFS4_READW_LT:
> diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
> index 60d7c59e7935..80c430c37ab7 100644
> --- a/fs/nfsd/nfsproc.c
> +++ b/fs/nfsd/nfsproc.c
> @@ -881,6 +881,7 @@ nfserrno (int errno)
>                 { nfserr_serverfault, -ENFILE },
>                 { nfserr_io, -EUCLEAN },
>                 { nfserr_perm, -ENOKEY },
> +               { nfserr_no_grace, -NFSERR_NO_GRACE},
>         };
>         int     i;
>  
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index c3c88fdb9b2a..9be479999109 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -997,6 +997,7 @@ static inline struct file *get_file(struct file
> *f)
>  #define FL_UNLOCK_PENDING      512 /* Lease is being broken */
>  #define FL_OFDLCK      1024    /* lock is "owned" by struct file */
>  #define FL_LAYOUT      2048    /* outstanding pNFS layout */
> +#define FL_RECLAIM     4096    /* reclaiming from a reboot server */
>  
>  #define FL_CLOSE_POSIX (FL_POSIX | FL_CLOSE)
>  

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com