linux-kernel - [ 062/180] SUNRPC: We must not use list_for_each_entry_safe() in rpc_wake

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Message-Id: <20121001225200.236039321@1wt.eu>
Date:	Tue, 02 Oct 2012 00:52:59 +0200
From:	Willy Tarreau <w@....eu>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	Trond Myklebust <Trond.Myklebust@...app.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Willy Tarreau <w@....eu>
Subject: [ 062/180] SUNRPC: We must not use list_for_each_entry_safe() in rpc_wake_up()

2.6.32-longterm review patch.  If anyone has any objections, please let me know.

------------------

From: Trond Myklebust <Trond.Myklebust@...app.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@...app.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@...app.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Signed-off-by: Willy Tarreau <w@....eu>
---
 net/sunrpc/sched.c |   15 +++++++++++----
 1 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/net/sunrpc/sched.c b/net/sunrpc/sched.c
index ac94477..9b3941d 100644
--- a/net/sunrpc/sched.c
+++ b/net/sunrpc/sched.c
@@ -485,14 +485,18 @@ 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--;
@@ -510,13 +514,16 @@ 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);
 		}
-- 
1.7.2.1.45.g54fbc



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