NFS: Add an asynchronous delegreturn operation for use in nfs_clear_inode

Otherwise, there is a potential deadlock if the last dput() from an NFSv4
close() or other asynchronous operation leads to nfs_clear_inode calling
the synchronous delegreturn.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 25 insertions, 4 deletions

diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index b03dcd8403f1..2dead8d1dd55 100644
--- a/fs/nfs/delegation.c
+++ b/fs/nfs/delegation.c
@@ -174,11 +174,11 @@ int nfs_inode_set_delegation(struct inode *inode, struct rpc_cred *cred, struct
         return status;
 }
 
-static int nfs_do_return_delegation(struct inode *inode, struct nfs_delegation *delegation)
+static int nfs_do_return_delegation(struct inode *inode, struct nfs_delegation *delegation, int issync)
 {
         int res = 0;
 
-        res = nfs4_proc_delegreturn(inode, delegation->cred, &delegation->stateid);
+        res = nfs4_proc_delegreturn(inode, delegation->cred, &delegation->stateid, issync);
         nfs_free_delegation(delegation);
         return res;
 }
@@ -208,7 +208,7 @@ static int __nfs_inode_return_delegation(struct inode *inode, struct nfs_delegat
         up_read(&clp->cl_sem);
         nfs_msync_inode(inode);
 
-        return nfs_do_return_delegation(inode, delegation);
+        return nfs_do_return_delegation(inode, delegation, 1);
 }
 
 static struct nfs_delegation *nfs_detach_delegation_locked(struct nfs_inode *nfsi, const nfs4_stateid *stateid)
@@ -228,6 +228,27 @@ nomatch:
         return NULL;
 }
 
+/*
+ * This function returns the delegation without reclaiming opens
+ * or protecting against delegation reclaims.
+ * It is therefore really only safe to be called from
+ * nfs4_clear_inode()
+ */
+void nfs_inode_return_delegation_noreclaim(struct inode *inode)
+{
+        struct nfs_client *clp = NFS_SERVER(inode)->nfs_client;
+        struct nfs_inode *nfsi = NFS_I(inode);
+        struct nfs_delegation *delegation;
+
+        if (rcu_dereference(nfsi->delegation) != NULL) {
+                spin_lock(&clp->cl_lock);
+                delegation = nfs_detach_delegation_locked(nfsi, NULL);
+                spin_unlock(&clp->cl_lock);
+                if (delegation != NULL)
+                        nfs_do_return_delegation(inode, delegation, 0);
+        }
+}
+
 int nfs_inode_return_delegation(struct inode *inode)
 {
         struct nfs_client *clp = NFS_SERVER(inode)->nfs_client;
@@ -388,7 +409,7 @@ static int recall_thread(void *data)
         nfs_msync_inode(inode);
 
         if (delegation != NULL)
-                nfs_do_return_delegation(inode, delegation);
+                nfs_do_return_delegation(inode, delegation, 1);
         iput(inode);
         module_put_and_exit(0);
 }