nfsd: fix callback restarts

Checking the rpc_client pointer is not a reliable way to detect
backchannel changes: cl_cb_client is changed only after shutting down
the rpc client, so the condition cl_cb_client = tk_client will always be
true.

Check the RPC_TASK_KILLED flag instead, and rewrite the code to avoid
the buggy cl_callbacks list and fix the lifetime rules due to double
calls of the ->prepare callback operations method for this retry case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

3 files changed, 24 insertions, 33 deletions

diff --git a/fs/nfsd/nfs4callback.c b/fs/nfsd/nfs4callback.c
index cd58b7cd3f1a..4c993aaf1e6e 100644
--- a/fs/nfsd/nfs4callback.c
+++ b/fs/nfsd/nfs4callback.c
@@ -879,13 +879,6 @@ static void nfsd4_cb_prepare(struct rpc_task *task, void *calldata)
                 if (!nfsd41_cb_get_slot(clp, task))
                         return;
         }
-        spin_lock(&clp->cl_lock);
-        if (list_empty(&cb->cb_per_client)) {
-                /* This is the first call, not a restart */
-                cb->cb_done = false;
-                list_add(&cb->cb_per_client, &clp->cl_callbacks);
-        }
-        spin_unlock(&clp->cl_lock);
         rpc_call_start(task);
 }
 
@@ -907,16 +900,21 @@ static void nfsd4_cb_done(struct rpc_task *task, void *calldata)
                         clp->cl_cb_session->se_cb_seq_nr);
         }
 
-        if (clp->cl_cb_client != task->tk_client) {
-                /* We're shutting down or changing cl_cb_client; leave
-                 * it to nfsd4_process_cb_update to restart the call if
-                 * necessary. */
+        /*
+         * If the backchannel connection was shut down while this
+         * task was queued, we need to resubmit it after setting up
+         * a new backchannel connection.
+         *
+         * Note that if we lost our callback connection permanently
+         * the submission code will error out, so we don't need to
+         * handle that case here.
+         */
+        if (task->tk_flags & RPC_TASK_KILLED) {
+                task->tk_status = 0;
+                cb->cb_need_restart = true;
                 return;
         }
 
-        if (cb->cb_done)
-                return;
-
         if (cb->cb_status) {
                 WARN_ON_ONCE(task->tk_status);
                 task->tk_status = cb->cb_status;
@@ -936,21 +934,17 @@ static void nfsd4_cb_done(struct rpc_task *task, void *calldata)
         default:
                 BUG();
         }
-        cb->cb_done = true;
 }
 
 static void nfsd4_cb_release(void *calldata)
 {
         struct nfsd4_callback *cb = calldata;
-        struct nfs4_client *clp = cb->cb_clp;
-
-        if (cb->cb_done) {
-                spin_lock(&clp->cl_lock);
-                list_del(&cb->cb_per_client);
-                spin_unlock(&clp->cl_lock);
 
+        if (cb->cb_need_restart)
+                nfsd4_run_cb(cb);
+        else
                 cb->cb_ops->release(cb);
-        }
+
 }
 
 static const struct rpc_call_ops nfsd4_cb_ops = {
@@ -1045,9 +1039,6 @@ static void nfsd4_process_cb_update(struct nfsd4_callback *cb)
                 nfsd4_mark_cb_down(clp, err);
                 return;
         }
-        /* Yay, the callback channel's back! Restart any callbacks: */
-        list_for_each_entry(cb, &clp->cl_callbacks, cb_per_client)
-                queue_work(callback_wq, &cb->cb_work);
 }
 
 static void
@@ -1058,8 +1049,12 @@ nfsd4_run_cb_work(struct work_struct *work)
         struct nfs4_client *clp = cb->cb_clp;
         struct rpc_clnt *clnt;
 
-        if (cb->cb_ops && cb->cb_ops->prepare)
-                cb->cb_ops->prepare(cb);
+        if (cb->cb_need_restart) {
+                cb->cb_need_restart = false;
+        } else {
+                if (cb->cb_ops && cb->cb_ops->prepare)
+                        cb->cb_ops->prepare(cb);
+        }
 
         if (clp->cl_flags & NFSD4_CLIENT_CB_FLAG_MASK)
                 nfsd4_process_cb_update(cb);
@@ -1085,9 +1080,8 @@ void nfsd4_init_cb(struct nfsd4_callback *cb, struct nfs4_client *clp,
         cb->cb_msg.rpc_resp = cb;
         cb->cb_ops = ops;
         INIT_WORK(&cb->cb_work, nfsd4_run_cb_work);
-        INIT_LIST_HEAD(&cb->cb_per_client);
         cb->cb_status = 0;
-        cb->cb_done = true;
+        cb->cb_need_restart = false;
 }
 
 void nfsd4_run_cb(struct nfsd4_callback *cb)
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 66067a291267..039f9c8a95e8 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1626,7 +1626,6 @@ static struct nfs4_client *alloc_client(struct xdr_netobj name)
         INIT_LIST_HEAD(&clp->cl_openowners);
         INIT_LIST_HEAD(&clp->cl_delegations);
         INIT_LIST_HEAD(&clp->cl_lru);
-        INIT_LIST_HEAD(&clp->cl_callbacks);
         INIT_LIST_HEAD(&clp->cl_revoked);
 #ifdef CONFIG_NFSD_PNFS
         INIT_LIST_HEAD(&clp->cl_lo_states);
diff --git a/fs/nfsd/state.h b/fs/nfsd/state.h
index e791985a7318..dbc4f85a5008 100644
--- a/fs/nfsd/state.h
+++ b/fs/nfsd/state.h
@@ -63,13 +63,12 @@ typedef struct {
 
 struct nfsd4_callback {
         struct nfs4_client *cb_clp;
-        struct list_head cb_per_client;
         u32 cb_minorversion;
         struct rpc_message cb_msg;
         struct nfsd4_callback_ops *cb_ops;
         struct work_struct cb_work;
         int cb_status;
-        bool cb_done;
+        bool cb_need_restart;
 };
 
 struct nfsd4_callback_ops {
@@ -334,7 +333,6 @@ struct nfs4_client {
         int                     cl_cb_state;
         struct nfsd4_callback   cl_cb_null;
         struct nfsd4_session    *cl_cb_session;
-        struct list_head        cl_callbacks; /* list of in-progress callbacks */
 
         /* for all client information that callback code might need: */
         spinlock_t              cl_lock;