[PATCH] kyber: Fix crash in kyber_finish_request()

[Yang Yang]

Kernel crash when requeue flush request.
It can be reproduced as below:

[    2.517297] Unable to handle kernel paging request at virtual address ffffffd8071c0b00
...
[    2.517468] pc : clear_bit+0x18/0x2c
[    2.517502] lr : sbitmap_queue_clear+0x40/0x228
[    2.517503] sp : ffffff800832bc60 pstate : 00c00145
...
[    2.517599] Process ksoftirqd/5 (pid: 51, stack limit = 0xffffff8008328000)
[    2.517602] Call trace:
[    2.517606]  clear_bit+0x18/0x2c
[    2.517619]  kyber_finish_request+0x74/0x80
[    2.517627]  blk_mq_requeue_request+0x3c/0xc0
[    2.517637]  __scsi_queue_insert+0x11c/0x148
[    2.517640]  scsi_softirq_done+0x114/0x130
[    2.517643]  blk_done_softirq+0x7c/0xb0
[    2.517651]  __do_softirq+0x208/0x3bc
[    2.517657]  run_ksoftirqd+0x34/0x60
[    2.517663]  smpboot_thread_fn+0x1c4/0x2c0
[    2.517667]  kthread+0x110/0x120
[    2.517669]  ret_from_fork+0x10/0x18

Signed-off-by: Yang Yang <yang.yang@xxxxxxxx>
---
 block/kyber-iosched.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index a38c5ab103d1..af73afe7a05c 100644
--- a/block/kyber-iosched.c
+++ b/block/kyber-iosched.c
@@ -611,6 +611,9 @@ static void kyber_finish_request(struct request *rq)
 {
 	struct kyber_queue_data *kqd = rq->q->elevator->elevator_data;
 
+	if (unlikely(!(rq->rq_flags & RQF_ELVPRIV)))
+		return;
+
 	rq_clear_domain_token(kqd, rq);
 }
 
-- 
2.17.1