NFSv4: Fix a potential sleep while atomic in nfs4_do_reclaim()

John Hubbard reports seeing the following stack trace:

nfs4_do_reclaim
   rcu_read_lock /* we are now in_atomic() and must not sleep */
       nfs4_purge_state_owners
           nfs4_free_state_owner
               nfs4_destroy_seqid_counter
                   rpc_destroy_wait_queue
                       cancel_delayed_work_sync
                           __cancel_work_timer
                               __flush_work
                                   start_flush_work
                                       might_sleep:
                                        (kernel/workqueue.c:2975: BUG)

The solution is to separate out the freeing of the state owners
from nfs4_purge_state_owners(), and perform that outside the atomic
context.

Reported-by: John Hubbard <jhubbard@nvidia.com>
Fixes: 0aaaf5c424c7f ("NFS: Cache state owners after files are closed")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

3 files changed, 28 insertions, 7 deletions

diff --git a/fs/nfs/nfs4_fs.h b/fs/nfs/nfs4_fs.h
index d778dad9a75e..3564da1ba8a1 100644
--- a/fs/nfs/nfs4_fs.h
+++ b/fs/nfs/nfs4_fs.h
@@ -465,7 +465,8 @@ static inline void nfs4_schedule_session_recovery(struct nfs4_session *session,
 
 extern struct nfs4_state_owner *nfs4_get_state_owner(struct nfs_server *, const struct cred *, gfp_t);
 extern void nfs4_put_state_owner(struct nfs4_state_owner *);
-extern void nfs4_purge_state_owners(struct nfs_server *);
+extern void nfs4_purge_state_owners(struct nfs_server *, struct list_head *);
+extern void nfs4_free_state_owners(struct list_head *head);
 extern struct nfs4_state * nfs4_get_open_state(struct inode *, struct nfs4_state_owner *);
 extern void nfs4_put_open_state(struct nfs4_state *);
 extern void nfs4_close_state(struct nfs4_state *, fmode_t);
diff --git a/fs/nfs/nfs4client.c b/fs/nfs/nfs4client.c
index 616393a01c06..da6204025a2d 100644
--- a/fs/nfs/nfs4client.c
+++ b/fs/nfs/nfs4client.c
@@ -758,9 +758,12 @@ out:
 
 static void nfs4_destroy_server(struct nfs_server *server)
 {
+        LIST_HEAD(freeme);
+
         nfs_server_return_all_delegations(server);
         unset_pnfs_layoutdriver(server);
-        nfs4_purge_state_owners(server);
+        nfs4_purge_state_owners(server, &freeme);
+        nfs4_free_state_owners(&freeme);
 }
 
 /*
diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index d03b9cf42bd0..a4e866b2b43b 100644
--- a/fs/nfs/nfs4state.c
+++ b/fs/nfs/nfs4state.c
@@ -624,24 +624,39 @@ void nfs4_put_state_owner(struct nfs4_state_owner *sp)
 /**
  * nfs4_purge_state_owners - Release all cached state owners
  * @server: nfs_server with cached state owners to release
+ * @head: resulting list of state owners
  *
  * Called at umount time.  Remaining state owners will be on
  * the LRU with ref count of zero.
+ * Note that the state owners are not freed, but are added
+ * to the list @head, which can later be used as an argument
+ * to nfs4_free_state_owners.
  */
-void nfs4_purge_state_owners(struct nfs_server *server)
+void nfs4_purge_state_owners(struct nfs_server *server, struct list_head *head)
 {
         struct nfs_client *clp = server->nfs_client;
         struct nfs4_state_owner *sp, *tmp;
-        LIST_HEAD(doomed);
 
         spin_lock(&clp->cl_lock);
         list_for_each_entry_safe(sp, tmp, &server->state_owners_lru, so_lru) {
-                list_move(&sp->so_lru, &doomed);
+                list_move(&sp->so_lru, head);
                 nfs4_remove_state_owner_locked(sp);
         }
         spin_unlock(&clp->cl_lock);
+}
 
-        list_for_each_entry_safe(sp, tmp, &doomed, so_lru) {
+/**
+ * nfs4_purge_state_owners - Release all cached state owners
+ * @head: resulting list of state owners
+ *
+ * Frees a list of state owners that was generated by
+ * nfs4_purge_state_owners
+ */
+void nfs4_free_state_owners(struct list_head *head)
+{
+        struct nfs4_state_owner *sp, *tmp;
+
+        list_for_each_entry_safe(sp, tmp, head, so_lru) {
                 list_del(&sp->so_lru);
                 nfs4_free_state_owner(sp);
         }
@@ -1865,12 +1880,13 @@ static int nfs4_do_reclaim(struct nfs_client *clp, const struct nfs4_state_recov
         struct nfs4_state_owner *sp;
         struct nfs_server *server;
         struct rb_node *pos;
+        LIST_HEAD(freeme);
         int status = 0;
 
 restart:
         rcu_read_lock();
         list_for_each_entry_rcu(server, &clp->cl_superblocks, client_link) {
-                nfs4_purge_state_owners(server);
+                nfs4_purge_state_owners(server, &freeme);
                 spin_lock(&clp->cl_lock);
                 for (pos = rb_first(&server->state_owners);
                      pos != NULL;
@@ -1899,6 +1915,7 @@ restart:
                 spin_unlock(&clp->cl_lock);
         }
         rcu_read_unlock();
+        nfs4_free_state_owners(&freeme);
         return 0;
 }