blk-ioc: protect ioc_destroy_icq() by 'queue_lock'

Currently, icq is tracked by both request_queue(icq->q_node) and
task(icq->ioc_node), and ioc_clear_queue() from elevator exit is not
safe because it can access the list without protection:

ioc_clear_queue			ioc_release_fn
 lock queue_lock
 list_splice
 /* move queue list to a local list */
 unlock queue_lock
 /*
  * lock is released, the local list
  * can be accessed through task exit.
  */

				lock ioc->lock
				while (!hlist_empty)
				 icq = hlist_entry
				 lock queue_lock
				  ioc_destroy_icq
				   delete icq->ioc_node
 while (!list_empty)
  icq = list_entry()		   list_del icq->q_node
  /*
   * This is not protected by any lock,
   * list_entry concurrent with list_del
   * is not safe.
   */

				 unlock queue_lock
				unlock ioc->lock

Fix this problem by protecting list 'icq->q_node' by queue_lock from
ioc_clear_queue().

Reported-and-tested-by: Pradeep Pragallapati <quic_pragalla@quicinc.com>
Link: https://lore.kernel.org/lkml/20230517084434.18932-1-quic_pragalla@quicinc.com/
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230531073435.2923422-1-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 63fc020..d5db92e 100644 (file)
--- a/block/blk-ioc.c
+++ b/block/blk-ioc.c
@@ -77,6 +77,10 @@ static void ioc_destroy_icq(struct io_cq *icq)
        struct elevator_type *et = q->elevator->type;
 
        lockdep_assert_held(&ioc->lock);
+       lockdep_assert_held(&q->queue_lock);
+
+       if (icq->flags & ICQ_DESTROYED)
+               return;
 
        radix_tree_delete(&ioc->icq_tree, icq->q->id);
        hlist_del_init(&icq->ioc_node);
@@ -128,12 +132,7 @@ static void ioc_release_fn(struct work_struct *work)
                        spin_lock(&q->queue_lock);
                        spin_lock(&ioc->lock);
 
-                       /*
-                        * The icq may have been destroyed when the ioc lock
-                        * was released.
-                        */
-                       if (!(icq->flags & ICQ_DESTROYED))
-                               ioc_destroy_icq(icq);
+                       ioc_destroy_icq(icq);
 
                        spin_unlock(&q->queue_lock);
                        rcu_read_unlock();
@@ -171,23 +170,20 @@ static bool ioc_delay_free(struct io_context *ioc)
  */
 void ioc_clear_queue(struct request_queue *q)
 {
-       LIST_HEAD(icq_list);
-
        spin_lock_irq(&q->queue_lock);
-       list_splice_init(&q->icq_list, &icq_list);
-       spin_unlock_irq(&q->queue_lock);
-
-       rcu_read_lock();
-       while (!list_empty(&icq_list)) {
+       while (!list_empty(&q->icq_list)) {
                struct io_cq *icq =
-                       list_entry(icq_list.next, struct io_cq, q_node);
+                       list_first_entry(&q->icq_list, struct io_cq, q_node);
 
+               /*
+                * Other context won't hold ioc lock to wait for queue_lock, see
+                * details in ioc_release_fn().
+                */
                spin_lock_irq(&icq->ioc->lock);
-               if (!(icq->flags & ICQ_DESTROYED))
-                       ioc_destroy_icq(icq);
+               ioc_destroy_icq(icq);
                spin_unlock_irq(&icq->ioc->lock);
        }
-       rcu_read_unlock();
+       spin_unlock_irq(&q->queue_lock);
 }
 #else /* CONFIG_BLK_ICQ */
 static inline void ioc_exit_icqs(struct io_context *ioc)