[RFC PATCH] thunderbolt: do not double dequeue a request

[Sergey Senozhatsky]

Some of our devices crash in tb_cfg_request_dequeue():

 general protection fault, probably for non-canonical address 0xdead000000000122: 0000 [#1] PREEMPT SMP NOPTI

 CPU: 6 PID: 91007 Comm: kworker/6:2 Tainted: G U W 6.6.65-06391-gbdec63d10750 #1 (HASH:cf42 1)
 RIP: 0010:tb_cfg_request_dequeue+0x2d/0xa0
 Call Trace:
 <TASK>
 ? tb_cfg_request_dequeue+0x2d/0xa0
 tb_cfg_request_work+0x33/0x80
 worker_thread+0x386/0x8f0
 kthread+0xed/0x110
 ret_from_fork+0x38/0x50
 ret_from_fork_asm+0x1b/0x30

The circumstances are unclear, however, the theory is that
tb_cfg_request_work() can be scheduled twice for a request:
first time via frame.callback from ring_work() and second
time from tb_cfg_request().  Both times kworkers will execute
tb_cfg_request_dequeue(), which results in double list_del()
from the ctl->request_queue (the list poison deference hints
at it: 0xdead000000000122).

Do not dequeue requests that don't have TB_CFG_REQUEST_ACTIVE
bit set.

Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
---
 drivers/thunderbolt/ctl.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/thunderbolt/ctl.c b/drivers/thunderbolt/ctl.c
index cd15e84c47f4..3ad15febc7df 100644
--- a/drivers/thunderbolt/ctl.c
+++ b/drivers/thunderbolt/ctl.c
@@ -151,7 +151,12 @@ static void tb_cfg_request_dequeue(struct tb_cfg_request *req)
 	struct tb_ctl *ctl = req->ctl;
 
 	mutex_lock(&ctl->request_queue_lock);
-	list_del(&req->list);
+	if (!test_bit(TB_CFG_REQUEST_ACTIVE, &req->flags)) {
+		mutex_unlock(&ctl->request_queue_lock);
+		return;
+	}
+
+	list_del_init(&req->list);
 	clear_bit(TB_CFG_REQUEST_ACTIVE, &req->flags);
 	if (test_bit(TB_CFG_REQUEST_CANCELED, &req->flags))
 		wake_up(&tb_cfg_request_cancel_queue);
-- 
2.49.0.395.g12beb8f557-goog