Hi, Jens
在 2023/05/31 15:34, Yu Kuai 写道:
From: Yu Kuai <yukuai3@xxxxxxxxxx>
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@xxxxxxxxxxx>
Link: https://lore.kernel.org/lkml/20230517084434.18932-1-quic_pragalla@xxxxxxxxxxx/
Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
block/blk-ioc.c | 30 +++++++++++++-----------------
1 file changed, 13 insertions(+), 17 deletions(-)
diff --git a/block/blk-ioc.c b/block/blk-ioc.c
index 63fc02042408..d5db92e62c43 100644
--- 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);
Sorry that I made a mistake here to use spin_lock_irq() for recursive
locking.
Should I resend this patch or send a new fix patch?
Sincerely apologize for this trouble.
Thanks,
Kuai
- 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)
