NFS: Fix a soft lockup in the delegation recovery code

Fix a soft lockup when NFS client delegation recovery is attempted
but the inode is in the process of being freed. When the
igrab(inode) call fails, and we have to restart the recovery process,
we need to ensure that we won't attempt to recover the same delegation
again.

Fixes: 45870d6909d5a ("NFSv4.1: Test delegation stateids when server...")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

2 files changed, 13 insertions, 8 deletions

diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index 70e5931f3c60..2f6b447cdd82 100644
--- a/fs/nfs/delegation.c
+++ b/fs/nfs/delegation.c
@@ -229,6 +229,8 @@ static struct inode *nfs_delegation_grab_inode(struct nfs_delegation *delegation
         spin_lock(&delegation->lock);
         if (delegation->inode != NULL)
                 inode = igrab(delegation->inode);
+        if (!inode)
+                set_bit(NFS_DELEGATION_INODE_FREEING, &delegation->flags);
         spin_unlock(&delegation->lock);
         return inode;
 }
@@ -944,10 +946,11 @@ restart:
         list_for_each_entry_rcu(server, &clp->cl_superblocks, client_link) {
                 list_for_each_entry_rcu(delegation, &server->delegations,
                                                                 super_list) {
-                        if (test_bit(NFS_DELEGATION_RETURNING,
-                                                &delegation->flags))
-                                continue;
-                        if (test_bit(NFS_DELEGATION_NEED_RECLAIM,
+                        if (test_bit(NFS_DELEGATION_INODE_FREEING,
+                                                &delegation->flags) ||
+                            test_bit(NFS_DELEGATION_RETURNING,
+                                                &delegation->flags) ||
+                            test_bit(NFS_DELEGATION_NEED_RECLAIM,
                                                 &delegation->flags) == 0)
                                 continue;
                         if (!nfs_sb_active(server->super))
@@ -1053,10 +1056,11 @@ restart:
         list_for_each_entry_rcu(server, &clp->cl_superblocks, client_link) {
                 list_for_each_entry_rcu(delegation, &server->delegations,
                                                                 super_list) {
-                        if (test_bit(NFS_DELEGATION_RETURNING,
-                                                &delegation->flags))
-                                continue;
-                        if (test_bit(NFS_DELEGATION_TEST_EXPIRED,
+                        if (test_bit(NFS_DELEGATION_INODE_FREEING,
+                                                &delegation->flags) ||
+                            test_bit(NFS_DELEGATION_RETURNING,
+                                                &delegation->flags) ||
+                            test_bit(NFS_DELEGATION_TEST_EXPIRED,
                                                 &delegation->flags) == 0)
                                 continue;
                         if (!nfs_sb_active(server->super))
diff --git a/fs/nfs/delegation.h b/fs/nfs/delegation.h
index dcbf3394ba0e..35b4b02c1ae0 100644
--- a/fs/nfs/delegation.h
+++ b/fs/nfs/delegation.h
@@ -34,6 +34,7 @@ enum {
         NFS_DELEGATION_RETURNING,
         NFS_DELEGATION_REVOKED,
         NFS_DELEGATION_TEST_EXPIRED,
+        NFS_DELEGATION_INODE_FREEING,
 };
 
 int nfs_inode_set_delegation(struct inode *inode, const struct cred *cred,