NFSv4: Fix up the dereferencing of delegation->inode

Without an extra lock, we cannot just assume that the delegation->inode is
valid when we're traversing the rcu-protected nfs_client lists. Use the
delegation->lock to ensure that it is truly valid.

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

1 files changed, 31 insertions, 8 deletions

diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
index e0cb4ee3b23e..13f2044a30be 100644
--- a/fs/nfs/delegation.c
+++ b/fs/nfs/delegation.c
@@ -134,6 +134,17 @@ static int nfs_do_return_delegation(struct inode *inode, struct nfs_delegation *
         return res;
 }
 
+static struct inode *nfs_delegation_grab_inode(struct nfs_delegation *delegation)
+{
+        struct inode *inode = NULL;
+
+        spin_lock(&delegation->lock);
+        if (delegation->inode != NULL)
+                inode = igrab(delegation->inode);
+        spin_unlock(&delegation->lock);
+        return inode;
+}
+
 static struct nfs_delegation *nfs_detach_delegation_locked(struct nfs_inode *nfsi, const nfs4_stateid *stateid)
 {
         struct nfs_delegation *delegation = rcu_dereference(nfsi->delegation);
@@ -145,6 +156,7 @@ static struct nfs_delegation *nfs_detach_delegation_locked(struct nfs_inode *nfs
                                 sizeof(delegation->stateid.data)) != 0)
                 goto nomatch_unlock;
         list_del_rcu(&delegation->super_list);
+        delegation->inode = NULL;
         nfsi->delegation_state = 0;
         rcu_assign_pointer(nfsi->delegation, NULL);
         spin_unlock(&delegation->lock);
@@ -298,9 +310,11 @@ void nfs_return_all_delegations(struct super_block *sb)
 restart:
         rcu_read_lock();
         list_for_each_entry_rcu(delegation, &clp->cl_delegations, super_list) {
-                if (delegation->inode->i_sb != sb)
-                        continue;
-                inode = igrab(delegation->inode);
+                inode = NULL;
+                spin_lock(&delegation->lock);
+                if (delegation->inode != NULL && delegation->inode->i_sb == sb)
+                        inode = igrab(delegation->inode);
+                spin_unlock(&delegation->lock);
                 if (inode == NULL)
                         continue;
                 spin_lock(&clp->cl_lock);
@@ -329,7 +343,7 @@ restart:
                 goto out;
         rcu_read_lock();
         list_for_each_entry_rcu(delegation, &clp->cl_delegations, super_list) {
-                inode = igrab(delegation->inode);
+                inode = nfs_delegation_grab_inode(delegation);
                 if (inode == NULL)
                         continue;
                 spin_lock(&clp->cl_lock);
@@ -376,7 +390,7 @@ void nfs_handle_cb_pathdown(struct nfs_client *clp)
 restart:
         rcu_read_lock();
         list_for_each_entry_rcu(delegation, &clp->cl_delegations, super_list) {
-                inode = igrab(delegation->inode);
+                inode = nfs_delegation_grab_inode(delegation);
                 if (inode == NULL)
                         continue;
                 spin_lock(&clp->cl_lock);
@@ -464,10 +478,14 @@ struct inode *nfs_delegation_find_inode(struct nfs_client *clp, const struct nfs
         struct inode *res = NULL;
         rcu_read_lock();
         list_for_each_entry_rcu(delegation, &clp->cl_delegations, super_list) {
-                if (nfs_compare_fh(fhandle, &NFS_I(delegation->inode)->fh) == 0) {
+                spin_lock(&delegation->lock);
+                if (delegation->inode != NULL &&
+                    nfs_compare_fh(fhandle, &NFS_I(delegation->inode)->fh) == 0) {
                         res = igrab(delegation->inode);
-                        break;
                 }
+                spin_unlock(&delegation->lock);
+                if (res != NULL)
+                        break;
         }
         rcu_read_unlock();
         return res;
@@ -491,17 +509,22 @@ void nfs_delegation_mark_reclaim(struct nfs_client *clp)
 void nfs_delegation_reap_unclaimed(struct nfs_client *clp)
 {
         struct nfs_delegation *delegation;
+        struct inode *inode;
 restart:
         rcu_read_lock();
         list_for_each_entry_rcu(delegation, &clp->cl_delegations, super_list) {
                 if ((delegation->flags & NFS_DELEGATION_NEED_RECLAIM) == 0)
                         continue;
+                inode = nfs_delegation_grab_inode(delegation);
+                if (inode == NULL)
+                        continue;
                 spin_lock(&clp->cl_lock);
-                delegation = nfs_detach_delegation_locked(NFS_I(delegation->inode), NULL);
+                delegation = nfs_detach_delegation_locked(NFS_I(inode), NULL);
                 spin_unlock(&clp->cl_lock);
                 rcu_read_unlock();
                 if (delegation != NULL)
                         nfs_free_delegation(delegation);
+                iput(inode);
                 goto restart;
         }
         rcu_read_unlock();