On 12/20/20 12:36 PM, Pavel Begunkov wrote:
> On 20/12/2020 19:34, Pavel Begunkov wrote:
>> On 14/12/2020 15:49, Xiaoguang Wang wrote:
>>> io_iopoll_complete() does not hold completion_lock to complete polled
>>> io, so in io_wq_submit_work(), we can not call io_req_complete() directly,
>>> to complete polled io, otherwise there maybe concurrent access to cqring,
>>> defer_list, etc, which is not safe. Commit dad1b1242fd5 ("io_uring: always
>>> let io_iopoll_complete() complete polled io") has fixed this issue, but
>>> Pavel reported that IOPOLL apart from rw can do buf reg/unreg requests(
>>> IORING_OP_PROVIDE_BUFFERS or IORING_OP_REMOVE_BUFFERS), so the fix is
>>> not good.
>>>
>>> Given that io_iopoll_complete() is always called under uring_lock, so here
>>> for polled io, we can also get uring_lock to fix this issue.
>>
>> This returns it to the state it was before fixing + mutex locking for
>> IOPOLL, and it's much better than having it half-broken as it is now.
>
> btw, comments are over 80, but that's minor.
I fixed that up, but I don't particularly like how 'req' is used after
calling complete. How about the below variant - same as before, just
using the ctx instead to determine if we need to lock it or not.
commit 253b60e7d8adcb980be91f77e64968a58d836b5e
Author: Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>
Date: Mon Dec 14 23:49:41 2020 +0800
io_uring: hold uring_lock while completing failed polled io in io_wq_submit_work()
io_iopoll_complete() does not hold completion_lock to complete polled io,
so in io_wq_submit_work(), we can not call io_req_complete() directly, to
complete polled io, otherwise there maybe concurrent access to cqring,
defer_list, etc, which is not safe. Commit dad1b1242fd5 ("io_uring: always
let io_iopoll_complete() complete polled io") has fixed this issue, but
Pavel reported that IOPOLL apart from rw can do buf reg/unreg requests(
IORING_OP_PROVIDE_BUFFERS or IORING_OP_REMOVE_BUFFERS), so the fix is not
good.
Given that io_iopoll_complete() is always called under uring_lock, so here
for polled io, we can also get uring_lock to fix this issue.
Fixes: dad1b1242fd5 ("io_uring: always let io_iopoll_complete() complete polled io")
Cc: <stable@xxxxxxxxxxxxxxx> # 5.5+
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@xxxxxxxxxxxxxxxxx>
Reviewed-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
[axboe: don't deref 'req' after completing it']
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
diff --git a/fs/io_uring.c b/fs/io_uring.c
index b27f61e3e0d6..0a8cf3fad955 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -6332,19 +6332,28 @@ static struct io_wq_work *io_wq_submit_work(struct io_wq_work *work)
}
if (ret) {
+ struct io_ring_ctx *lock_ctx = NULL;
+
+ if (req->ctx->flags & IORING_SETUP_IOPOLL)
+ lock_ctx = req->ctx;
+
/*
- * io_iopoll_complete() does not hold completion_lock to complete
- * polled io, so here for polled io, just mark it done and still let
- * io_iopoll_complete() complete it.
+ * io_iopoll_complete() does not hold completion_lock to
+ * complete polled io, so here for polled io, we can not call
+ * io_req_complete() directly, otherwise there maybe concurrent
+ * access to cqring, defer_list, etc, which is not safe. Given
+ * that io_iopoll_complete() is always called under uring_lock,
+ * so here for polled io, we also get uring_lock to complete
+ * it.
*/
- if (req->ctx->flags & IORING_SETUP_IOPOLL) {
- struct kiocb *kiocb = &req->rw.kiocb;
+ if (lock_ctx)
+ mutex_lock(&lock_ctx->uring_lock);
- kiocb_done(kiocb, ret, NULL);
- } else {
- req_set_fail_links(req);
- io_req_complete(req, ret);
- }
+ req_set_fail_links(req);
+ io_req_complete(req, ret);
+
+ if (lock_ctx)
+ mutex_unlock(&lock_ctx->uring_lock);
}
return io_steal_work(req);
--
Jens Axboe
