[PATCH v3 4/4] io_uring: Fix double list add in io_queue_async_work()

[Muchun Song]

If we queue work in io_poll_wake(), it will leads to list double
add. So we should add the list when the callback func is the
io_sq_wq_submit_work.

The following oops was seen:

    list_add double add: new=ffff9ca6a8f1b0e0, prev=ffff9ca62001cee8,
    next=ffff9ca6a8f1b0e0.
    ------------[ cut here ]------------
    kernel BUG at lib/list_debug.c:31!
    Call Trace:
     <IRQ>
     io_poll_wake+0xf3/0x230
     __wake_up_common+0x91/0x170
     __wake_up_common_lock+0x7a/0xc0
     io_commit_cqring+0xea/0x280
     ? blkcg_iolatency_done_bio+0x2b/0x610
     io_cqring_add_event+0x3e/0x60
     io_complete_rw+0x58/0x80
     dio_complete+0x106/0x250
     blk_update_request+0xa0/0x3b0
     blk_mq_end_request+0x1a/0x110
     blk_mq_complete_request+0xd0/0xe0
     nvme_irq+0x129/0x270 [nvme]
     __handle_irq_event_percpu+0x7b/0x190
     handle_irq_event_percpu+0x30/0x80
     handle_irq_event+0x3c/0x60
     handle_edge_irq+0x91/0x1e0
     do_IRQ+0x4d/0xd0
     common_interrupt+0xf/0xf

Fixes: 1c4404efcf2c ("io_uring: make sure async workqueue is canceled on exit")
Reported-by: Jiachen Zhang <zhangjiachen.jaycee@xxxxxxxxxxxxx>
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 fs/io_uring.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index c65f78f395655..a7cfe976480d8 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -513,12 +513,14 @@ static inline void io_queue_async_work(struct io_ring_ctx *ctx,
 		}
 	}
 
-	req->files = current->files;
+	if (req->work.func == io_sq_wq_submit_work) {
+		req->files = current->files;
 
-	spin_lock_irqsave(&ctx->task_lock, flags);
-	list_add(&req->task_list, &ctx->task_list);
-	req->work_task = NULL;
-	spin_unlock_irqrestore(&ctx->task_lock, flags);
+		spin_lock_irqsave(&ctx->task_lock, flags);
+		list_add(&req->task_list, &ctx->task_list);
+		req->work_task = NULL;
+		spin_unlock_irqrestore(&ctx->task_lock, flags);
+	}
 
 	queue_work(ctx->sqo_wq[rw], &req->work);
 }
@@ -667,6 +669,7 @@ static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx,
 		state->cur_req++;
 	}
 
+	INIT_LIST_HEAD(&req->task_list);
 	req->file = NULL;
 	req->ctx = ctx;
 	req->flags = 0;
-- 
2.11.0