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Subject[ 097/149] SUNRPC: We must not use list_for_each_entry_safe() in rpc_wake_up()
3.2-stable review patch.  If anyone has any objections, please let me know.

------------------
From: Trond Myklebust <Trond.Myklebust@netapp.com>

commit 540a0f7584169651f485e8ab67461fcb06934e38 upstream.

The problem is that for the case of priority queues, we
have to assume that __rpc_remove_wait_queue_priority will move new
elements from the tk_wait.links lists into the queue->tasks[] list.
We therefore cannot use list_for_each_entry_safe() on queue->tasks[],
since that will skip these new tasks that __rpc_remove_wait_queue_priority
is adding.

Without this fix, rpc_wake_up and rpc_wake_up_status will both fail
to wake up all functions on priority wait queues, which can result
in some nasty hangs.

Reported-by: Andy Adamson <andros@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
net/sunrpc/sched.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -500,14 +500,18 @@ EXPORT_SYMBOL_GPL(rpc_wake_up_next);
*/
void rpc_wake_up(struct rpc_wait_queue *queue)
{
- struct rpc_task *task, *next;
struct list_head *head;

spin_lock_bh(&queue->lock);
head = &queue->tasks[queue->maxpriority];
for (;;) {
- list_for_each_entry_safe(task, next, head, u.tk_wait.list)
+ while (!list_empty(head)) {
+ struct rpc_task *task;
+ task = list_first_entry(head,
+ struct rpc_task,
+ u.tk_wait.list);
rpc_wake_up_task_queue_locked(queue, task);
+ }
if (head == &queue->tasks[0])
break;
head--;
@@ -525,13 +529,16 @@ EXPORT_SYMBOL_GPL(rpc_wake_up);
*/
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);
head = &queue->tasks[queue->maxpriority];
for (;;) {
- list_for_each_entry_safe(task, next, head, u.tk_wait.list) {
+ while (!list_empty(head)) {
+ struct rpc_task *task;
+ task = list_first_entry(head,
+ struct rpc_task,
+ u.tk_wait.list);
task->tk_status = status;
rpc_wake_up_task_queue_locked(queue, task);
}



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