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SUNRPC: Tighten up the task locking rules in __rpc_execute() 

We should probably not be testing any flags after we've cleared the
RPC_TASK_RUNNING flag, since rpc_make_runnable() is then free to assign the
rpc_task to another workqueue, which may then destroy it.

We can fix any races with rpc_make_runnable() by ensuring that we only
clear the RPC_TASK_RUNNING flag while holding the rpc_wait_queue->lock that
the task is supposed to be sleeping on (and then checking whether or not
the task really is sleeping).

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
This commit is contained in:
Trond Myklebust 2009-03-10 20:33:16 -04:00
parent 16b71fdf97
commit eb9b55ab4d
1 changed files with 20 additions and 13 deletions
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33
net/sunrpc/sched.c
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@ -293,11 +293,6 @@ static void rpc_make_runnable(struct rpc_task *task)
rpc_clear_queued(task);
if (rpc_test_and_set_running(task))
return;
/* We might have raced */
if (RPC_IS_QUEUED(task)) {
rpc_clear_running(task);
return;
}
if (RPC_IS_ASYNC(task)) {
int status;
@ -607,7 +602,9 @@ void rpc_release_calldata(const struct rpc_call_ops *ops, void *calldata)
*/
static void __rpc_execute(struct rpc_task *task)
{
int status = 0;
struct rpc_wait_queue *queue;
int task_is_async = RPC_IS_ASYNC(task);
int status = 0;
dprintk("RPC: %5u __rpc_execute flags=0x%x\n",
task->tk_pid, task->tk_flags);
@ -647,15 +644,25 @@ static void __rpc_execute(struct rpc_task *task)
*/
if (!RPC_IS_QUEUED(task))
continue;
rpc_clear_running(task);
if (RPC_IS_ASYNC(task)) {
/* Careful! we may have raced... */
if (RPC_IS_QUEUED(task))
return;
if (rpc_test_and_set_running(task))
return;
/*
* The queue->lock protects against races with
* rpc_make_runnable().
*
* Note that once we clear RPC_TASK_RUNNING on an asynchronous
* rpc_task, rpc_make_runnable() can assign it to a
* different workqueue. We therefore cannot assume that the
* rpc_task pointer may still be dereferenced.
*/
queue = task->tk_waitqueue;
spin_lock_bh(&queue->lock);
if (!RPC_IS_QUEUED(task)) {
spin_unlock_bh(&queue->lock);
continue;
}
rpc_clear_running(task);
spin_unlock_bh(&queue->lock);
if (task_is_async)
return;
/* sync task: sleep here */
dprintk("RPC: %5u sync task going to sleep\n", task->tk_pid);