> On Feb 3, 2015, at 4:59 PM, Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx> wrote:
>
> If we already hold a delegation, there should be no reason for the
> server to issue it to us again. Unfortunately, there appear to be
> servers out there that engage in this practice. While it is often
> harmless to do so, there is one case where this creates a problem
> and that is when the client is in the process of returning that
> delegation.
> This patch uses the NFSv4.1 NFS4_SHARE_WANT_NO_DELEG flag to inform
> the server not to return a delegation in these cases.
>
> Signed-off-by: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
> ---
> fs/nfs/nfs4proc.c | 25 ++++++++++++++++++++++---
> 1 file changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
> index cd4295d84d54..fb41624bafc9 100644
> --- a/fs/nfs/nfs4proc.c
> +++ b/fs/nfs/nfs4proc.c
> @@ -942,8 +942,10 @@ static bool nfs4_clear_cap_atomic_open_v1(struct nfs_server *server,
>
> static u32
> nfs4_map_atomic_open_share(struct nfs_server *server,
> + struct inode *inode,
> fmode_t fmode, int openflags)
> {
> + struct nfs_delegation *delegation;
> u32 res = 0;
>
> switch (fmode & (FMODE_READ | FMODE_WRITE)) {
> @@ -959,8 +961,25 @@ nfs4_map_atomic_open_share(struct nfs_server *server,
> if (!(server->caps & NFS_CAP_ATOMIC_OPEN_V1))
> goto out;
> /* Want no delegation if we're using O_DIRECT */
> - if (openflags & O_DIRECT)
> + if (openflags & O_DIRECT) {
> res |= NFS4_SHARE_WANT_NO_DELEG;
> + goto out;
> + }
> + if (inode == NULL)
> + goto out;
> + rcu_read_lock();
> + delegation = rcu_dereference(NFS_I(inode)->delegation);
> + /*
> + * If we have a delegation, either ask for an upgrade or ask for
> + * no delegation
> + */
> + if (delegation) {
> + if ((fmode & FMODE_WRITE) && !(delegation->type & FMODE_WRITE))
> + res |= NFS4_SHARE_WANT_WRITE_DELEG;
> + else
> + res |= NFS4_SHARE_WANT_NO_DELEG;
> + }
> + rcu_read_unlock();
> out:
> return res;
> }
> @@ -1028,7 +1047,7 @@ static struct nfs4_opendata *nfs4_opendata_alloc(struct dentry *dentry,
> p->o_arg.open_flags = flags;
> p->o_arg.fmode = fmode & (FMODE_READ|FMODE_WRITE);
> p->o_arg.share_access = nfs4_map_atomic_open_share(server,
> - fmode, flags);
> + dentry->d_inode, fmode, flags);
> /* don't put an ACCESS op in OPEN compound if O_EXCL, because ACCESS
> * will return permission denied for all bits until close */
> if (!(flags & O_EXCL)) {
> @@ -2724,7 +2743,7 @@ static void nfs4_close_prepare(struct rpc_task *task, void *data)
> }
> calldata->arg.share_access =
> nfs4_map_atomic_open_share(NFS_SERVER(inode),
> - calldata->arg.fmode, 0);
> + NULL, calldata->arg.fmode, 0);
>
> nfs_fattr_init(calldata->res.fattr);
> calldata->timestamp = jiffies;
> --
> 2.1.0
>
Hi Trond,
Do you see this of helping with the race? We won’t find a delegation on the racing open as it has been detached from the inode. For the other patch, aren’t we already checking if we can do a local open by checking for the delegation (can_open_delegated())?
Thanks.
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