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>

1 files changed, 4 insertions, 1 deletions

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);
 }
 
 /*