nfs41: nfs41: fix state manager deadlock in session reset

If the session is reset during state recovery, the state manager thread can
sleep on the slot_tbl_waitq causing a deadlock.

Add a completion framework to the session.  Have the state manager thread set
a new session state (NFS4CLNT_SESSION_DRAINING) and wait for the session slot
table to drain.

Signal the state manager thread in nfs41_sequence_free_slot when the
NFS4CLNT_SESSION_DRAINING bit is set and the session is drained.

Reported-by: Trond Myklebust <trond@netapp.com>
Signed-off-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

4 files changed, 34 insertions, 9 deletions

diff --git a/fs/nfs/nfs4_fs.h b/fs/nfs/nfs4_fs.h
index e9ecd6bf9257..5c7740178a08 100644
--- a/fs/nfs/nfs4_fs.h
+++ b/fs/nfs/nfs4_fs.h
@@ -45,6 +45,7 @@ enum nfs4_client_state {
         NFS4CLNT_RECLAIM_NOGRACE,
         NFS4CLNT_DELEGRETURN,
         NFS4CLNT_SESSION_RESET,
+        NFS4CLNT_SESSION_DRAINING,
 };
 
 /*
diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
index fb62919f7f2c..c1bc9cad5e85 100644
--- a/fs/nfs/nfs4proc.c
+++ b/fs/nfs/nfs4proc.c
@@ -361,6 +361,16 @@ void nfs41_sequence_free_slot(const struct nfs_client *clp,
         }
         nfs4_free_slot(tbl, res->sr_slotid);
         res->sr_slotid = NFS4_MAX_SLOT_TABLE;
+
+        /* Signal state manager thread if session is drained */
+        if (test_bit(NFS4CLNT_SESSION_DRAINING, &clp->cl_state)) {
+                spin_lock(&tbl->slot_tbl_lock);
+                if (tbl->highest_used_slotid == -1) {
+                        dprintk("%s COMPLETE: Session Drained\n", __func__);
+                        complete(&clp->cl_session->complete);
+                }
+                spin_unlock(&tbl->slot_tbl_lock);
+        }
 }
 
 static void nfs41_sequence_done(struct nfs_client *clp,
@@ -457,15 +467,11 @@ static int nfs41_setup_sequence(struct nfs4_session *session,
 
         spin_lock(&tbl->slot_tbl_lock);
         if (test_bit(NFS4CLNT_SESSION_RESET, &session->clp->cl_state)) {
-                if (tbl->highest_used_slotid != -1) {
-                        rpc_sleep_on(&tbl->slot_tbl_waitq, task, NULL);
-                        spin_unlock(&tbl->slot_tbl_lock);
-                        dprintk("<-- %s: Session reset: draining\n", __func__);
-                        return -EAGAIN;
-                }
-
-                /* The slot table is empty; start the reset thread */
-                dprintk("%s Session Reset\n", __func__);
+                /*
+                 * The state manager will wait until the slot table is empty.
+                 * Schedule the reset thread
+                 */
+                dprintk("%s Schedule Session Reset\n", __func__);
                 rpc_sleep_on(&tbl->slot_tbl_waitq, task, NULL);
                 nfs4_schedule_state_manager(session->clp);
                 spin_unlock(&tbl->slot_tbl_lock);
@@ -4506,6 +4512,7 @@ static int nfs4_reset_slot_tables(struct nfs4_session *session)
                         1);
         if (status)
                 return status;
+        init_completion(&session->complete);
 
         status = nfs4_reset_slot_table(&session->bc_slot_table,
                         session->bc_attrs.max_reqs,
@@ -4608,6 +4615,7 @@ struct nfs4_session *nfs4_alloc_session(struct nfs_client *clp)
          * nfs_client struct
          */
         clp->cl_cons_state = NFS_CS_SESSION_INITING;
+        init_completion(&session->complete);
 
         tbl = &session->fc_slot_table;
         spin_lock_init(&tbl->slot_tbl_lock);
diff --git a/fs/nfs/nfs4state.c b/fs/nfs/nfs4state.c
index f56f6be5e314..3c1433598b60 100644
--- a/fs/nfs/nfs4state.c
+++ b/fs/nfs/nfs4state.c
@@ -1181,8 +1181,23 @@ static void nfs4_session_recovery_handle_error(struct nfs_client *clp, int err)
 
 static int nfs4_reset_session(struct nfs_client *clp)
 {
+        struct nfs4_session *ses = clp->cl_session;
+        struct nfs4_slot_table *tbl = &ses->fc_slot_table;
         int status;
 
+        INIT_COMPLETION(ses->complete);
+        spin_lock(&tbl->slot_tbl_lock);
+        if (tbl->highest_used_slotid != -1) {
+                set_bit(NFS4CLNT_SESSION_DRAINING, &clp->cl_state);
+                spin_unlock(&tbl->slot_tbl_lock);
+                status = wait_for_completion_interruptible(&ses->complete);
+                clear_bit(NFS4CLNT_SESSION_DRAINING, &clp->cl_state);
+                if (status) /* -ERESTARTSYS */
+                        goto out;
+        } else {
+                spin_unlock(&tbl->slot_tbl_lock);
+        }
+
         status = nfs4_proc_destroy_session(clp->cl_session);
         if (status && status != -NFS4ERR_BADSESSION &&
             status != -NFS4ERR_DEADSESSION) {
diff --git a/include/linux/nfs_fs_sb.h b/include/linux/nfs_fs_sb.h
index 320569eabe3b..34fc6be5bfcf 100644
--- a/include/linux/nfs_fs_sb.h
+++ b/include/linux/nfs_fs_sb.h
@@ -209,6 +209,7 @@ struct nfs4_session {
         unsigned long                   session_state;
         u32                             hash_alg;
         u32                             ssv_len;
+        struct completion               complete;
 
         /* The fore and back channel */
         struct nfs4_channel_attrs       fc_attrs;