[PATCH 2/4] io_uring: handle EAGAIN iopoll

[Pavel Begunkov <asml.silence@gmail.com>]

req->iopoll() is not necessarily called by a task that submitted a
request. Because of that, it's dangerous to grab_env() and punt async
on -EGAIN, potentially grabbinf another task's mm and corrupting its
memory.

Do resubmit from the submitter task context.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index bb0dfc450db5..595d2bbb31b1 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -884,6 +884,8 @@ enum io_mem_account {
 	ACCT_PINNED,
 };
 
+static void io_complete_rw_common(struct kiocb *kiocb, long res);
+static bool io_rw_reissue(struct io_kiocb *req, long res);
 static void io_wq_submit_work(struct io_wq_work **workptr);
 static void io_cqring_fill_event(struct io_kiocb *req, long res);
 static void io_put_req(struct io_kiocb *req);
@@ -1756,8 +1758,11 @@ static void io_iopoll_queue(struct list_head *again)
 	do {
 		req = list_first_entry(again, struct io_kiocb, list);
 		list_del(&req->list);
-		refcount_inc(&req->refs);
-		io_queue_async_work(req);
+
+		if (!io_rw_reissue(req, -EAGAIN)) {
+			io_complete_rw_common(&req->rw.kiocb, -EAGAIN);
+			io_put_req(req);
+		}
 	} while (!list_empty(again));
 }
 
@@ -1930,6 +1935,8 @@ static int io_iopoll_check(struct io_ring_ctx *ctx, unsigned *nr_events,
 		 */
 		if (!(++iters & 7)) {
 			mutex_unlock(&ctx->uring_lock);
+			if (current->task_works)
+				task_work_run();
 			mutex_lock(&ctx->uring_lock);
 		}
 
@@ -2288,6 +2295,7 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe,
 		kiocb->ki_complete = io_complete_rw_iopoll;
 		req->result = 0;
 		req->iopoll_completed = 0;
+		io_get_req_task(req);
 	} else {
 		if (kiocb->ki_flags & IOCB_HIPRI)
 			return -EINVAL;
-- 
2.24.0