SUNRPC: Fix a potential race in rpc_wake_up_task()

Use RCU to ensure that we can safely call rpc_finish_wakeup after we've
called __rpc_do_wake_up_task. If not, there is a theoretical race, in which
the rpc_task finishes executing, and gets freed first.

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

1 files changed, 20 insertions, 10 deletions

diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
index 66d01365f3a5..6b808c03fb72 100644
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -427,16 +427,19 @@ __rpc_default_timer(struct rpc_task *task)
  */
 void rpc_wake_up_task(struct rpc_task *task)
 {
+        rcu_read_lock_bh();
         if (rpc_start_wakeup(task)) {
                 if (RPC_IS_QUEUED(task)) {
                         struct rpc_wait_queue *queue = task->u.tk_wait.rpc_waitq;
 
-                        spin_lock_bh(&queue->lock);
+                        /* Note: we're already in a bh-safe context */
+                        spin_lock(&queue->lock);
                         __rpc_do_wake_up_task(task);
-                        spin_unlock_bh(&queue->lock);
+                        spin_unlock(&queue->lock);
                 }
                 rpc_finish_wakeup(task);
         }
+        rcu_read_unlock_bh();
 }
 
 /*
@@ -499,14 +502,16 @@ struct rpc_task * rpc_wake_up_next(struct rpc_wait_queue *queue)
         struct rpc_task *task = NULL;
 
         dprintk("RPC:      wake_up_next(%p \"%s\")\n", queue, rpc_qname(queue));
-        spin_lock_bh(&queue->lock);
+        rcu_read_lock_bh();
+        spin_lock(&queue->lock);
         if (RPC_IS_PRIORITY(queue))
                 task = __rpc_wake_up_next_priority(queue);
         else {
                 task_for_first(task, &queue->tasks[0])
                         __rpc_wake_up_task(task);
         }
-        spin_unlock_bh(&queue->lock);
+        spin_unlock(&queue->lock);
+        rcu_read_unlock_bh();
 
         return task;
 }
@@ -522,7 +527,8 @@ void rpc_wake_up(struct rpc_wait_queue *queue)
         struct rpc_task *task, *next;
         struct list_head *head;
 
-        spin_lock_bh(&queue->lock);
+        rcu_read_lock_bh();
+        spin_lock(&queue->lock);
         head = &queue->tasks[queue->maxpriority];
         for (;;) {
                 list_for_each_entry_safe(task, next, head, u.tk_wait.list)
@@ -531,7 +537,8 @@ void rpc_wake_up(struct rpc_wait_queue *queue)
                         break;
                 head--;
         }
-        spin_unlock_bh(&queue->lock);
+        spin_unlock(&queue->lock);
+        rcu_read_unlock_bh();
 }
 
 /**
@@ -546,7 +553,8 @@ void rpc_wake_up_status(struct rpc_wait_queue *queue, int status)
         struct rpc_task *task, *next;
         struct list_head *head;
 
-        spin_lock_bh(&queue->lock);
+        rcu_read_lock_bh();
+        spin_lock(&queue->lock);
         head = &queue->tasks[queue->maxpriority];
         for (;;) {
                 list_for_each_entry_safe(task, next, head, u.tk_wait.list) {
@@ -557,7 +565,8 @@ void rpc_wake_up_status(struct rpc_wait_queue *queue, int status)
                         break;
                 head--;
         }
-        spin_unlock_bh(&queue->lock);
+        spin_unlock(&queue->lock);
+        rcu_read_unlock_bh();
 }
 
 static void __rpc_atrun(struct rpc_task *task)
@@ -817,8 +826,9 @@ rpc_alloc_task(void)
         return (struct rpc_task *)mempool_alloc(rpc_task_mempool, GFP_NOFS);
 }
 
-static void rpc_free_task(struct rpc_task *task)
+static void rpc_free_task(struct rcu_head *rcu)
 {
+        struct rpc_task *task = container_of(rcu, struct rpc_task, u.tk_rcu);
         dprintk("RPC: %4d freeing task\n", task->tk_pid);
         mempool_free(task, rpc_task_mempool);
 }
@@ -872,7 +882,7 @@ void rpc_put_task(struct rpc_task *task)
                 task->tk_client = NULL;
         }
         if (task->tk_flags & RPC_TASK_DYNAMIC)
-                rpc_free_task(task);
+                call_rcu_bh(&task->u.tk_rcu, rpc_free_task);
         if (tk_ops->rpc_release)
                 tk_ops->rpc_release(calldata);
 }