1 files changed, 36 insertions, 16 deletions

diff --git a/io_uring/poll.c b/io_uring/poll.c
index ee7da6150ec4..2ac1366adbd7 100644
--- a/io_uring/poll.c
+++ b/io_uring/poll.c
@@ -223,21 +223,22 @@ enum {
 	IOU_POLL_DONE = 0,
 	IOU_POLL_NO_ACTION = 1,
 	IOU_POLL_REMOVE_POLL_USE_RES = 2,
+	IOU_POLL_REISSUE = 3,
 };
 
 /*
  * All poll tw should go through this. Checks for poll events, manages
  * references, does rewait, etc.
  *
- * Returns a negative error on failure. IOU_POLL_NO_ACTION when no action require,
- * which is either spurious wakeup or multishot CQE is served.
- * IOU_POLL_DONE when it's done with the request, then the mask is stored in req->cqe.res.
- * IOU_POLL_REMOVE_POLL_USE_RES indicates to remove multishot poll and that the result
- * is stored in req->cqe.
+ * Returns a negative error on failure. IOU_POLL_NO_ACTION when no action
+ * require, which is either spurious wakeup or multishot CQE is served.
+ * IOU_POLL_DONE when it's done with the request, then the mask is stored in
+ * req->cqe.res. IOU_POLL_REMOVE_POLL_USE_RES indicates to remove multishot
+ * poll and that the result is stored in req->cqe.
  */
 static int io_poll_check_events(struct io_kiocb *req, bool *locked)
 {
-	int v, ret;
+	int v;
 
 	/* req->task == current here, checking PF_EXITING is safe */
 	if (unlikely(req->task->flags & PF_EXITING))
@@ -276,10 +277,19 @@ static int io_poll_check_events(struct io_kiocb *req, bool *locked)
 		if (!req->cqe.res) {
 			struct poll_table_struct pt = { ._key = req->apoll_events };
 			req->cqe.res = vfs_poll(req->file, &pt) & req->apoll_events;
+			/*
+			 * We got woken with a mask, but someone else got to
+			 * it first. The above vfs_poll() doesn't add us back
+			 * to the waitqueue, so if we get nothing back, we
+			 * should be safe and attempt a reissue.
+			 */
+			if (unlikely(!req->cqe.res)) {
+				/* Multishot armed need not reissue */
+				if (!(req->apoll_events & EPOLLONESHOT))
+					continue;
+				return IOU_POLL_REISSUE;
+			}
 		}
-
-		if ((unlikely(!req->cqe.res)))
-			continue;
 		if (req->apoll_events & EPOLLONESHOT)
 			return IOU_POLL_DONE;
 
@@ -294,7 +304,7 @@ static int io_poll_check_events(struct io_kiocb *req, bool *locked)
 				return IOU_POLL_REMOVE_POLL_USE_RES;
 			}
 		} else {
-			ret = io_poll_issue(req, locked);
+			int ret = io_poll_issue(req, locked);
 			if (ret == IOU_STOP_MULTISHOT)
 				return IOU_POLL_REMOVE_POLL_USE_RES;
 			if (ret < 0)
@@ -330,6 +340,9 @@ static void io_poll_task_func(struct io_kiocb *req, bool *locked)
 
 			poll = io_kiocb_to_cmd(req, struct io_poll);
 			req->cqe.res = mangle_poll(req->cqe.res & poll->events);
+		} else if (ret == IOU_POLL_REISSUE) {
+			io_req_task_submit(req, locked);
+			return;
 		} else if (ret != IOU_POLL_REMOVE_POLL_USE_RES) {
 			req->cqe.res = ret;
 			req_set_fail(req);
@@ -342,7 +355,7 @@ static void io_poll_task_func(struct io_kiocb *req, bool *locked)
 
 		if (ret == IOU_POLL_REMOVE_POLL_USE_RES)
 			io_req_task_complete(req, locked);
-		else if (ret == IOU_POLL_DONE)
+		else if (ret == IOU_POLL_DONE || ret == IOU_POLL_REISSUE)
 			io_req_task_submit(req, locked);
 		else
 			io_req_defer_failed(req, ret);
@@ -533,6 +546,14 @@ static bool io_poll_can_finish_inline(struct io_kiocb *req,
 	return pt->owning || io_poll_get_ownership(req);
 }
 
+static void io_poll_add_hash(struct io_kiocb *req)
+{
+	if (req->flags & REQ_F_HASH_LOCKED)
+		io_poll_req_insert_locked(req);
+	else
+		io_poll_req_insert(req);
+}
+
 /*
  * Returns 0 when it's handed over for polling. The caller owns the requests if
  * it returns non-zero, but otherwise should not touch it. Negative values
@@ -591,18 +612,17 @@ static int __io_arm_poll_handler(struct io_kiocb *req,
 
 	if (mask &&
 	   ((poll->events & (EPOLLET|EPOLLONESHOT)) == (EPOLLET|EPOLLONESHOT))) {
-		if (!io_poll_can_finish_inline(req, ipt))
+		if (!io_poll_can_finish_inline(req, ipt)) {
+			io_poll_add_hash(req);
 			return 0;
+		}
 		io_poll_remove_entries(req);
 		ipt->result_mask = mask;
 		/* no one else has access to the req, forget about the ref */
 		return 1;
 	}
 
-	if (req->flags & REQ_F_HASH_LOCKED)
-		io_poll_req_insert_locked(req);
-	else
-		io_poll_req_insert(req);
+	io_poll_add_hash(req);
 
 	if (mask && (poll->events & EPOLLET) &&
 	    io_poll_can_finish_inline(req, ipt)) {