io_uring: allow re-poll if we made progress

We currently check REQ_F_POLLED before arming async poll for a
notification to retry. If it's set, then we don't allow poll and will
punt to io-wq instead. This is done to prevent a situation where a buggy
driver will repeatedly return that there's space/data available yet we
get -EAGAIN.

However, if we already transferred data, then it should be safe to rely
on poll again. Gate the check on whether or not REQ_F_PARTIAL_IO is
also set.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index e18d889..97ed7f4 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -6266,7 +6266,9 @@ static int io_arm_poll_handler(struct io_kiocb *req, unsigned issue_flags)
 
        if (!def->pollin && !def->pollout)
                return IO_APOLL_ABORTED;
-       if (!file_can_poll(req->file) || (req->flags & REQ_F_POLLED))
+       if (!file_can_poll(req->file))
+               return IO_APOLL_ABORTED;
+       if ((req->flags & (REQ_F_POLLED|REQ_F_PARTIAL_IO)) == REQ_F_POLLED)
                return IO_APOLL_ABORTED;
 
        if (def->pollin) {
@@ -6281,8 +6283,10 @@ static int io_arm_poll_handler(struct io_kiocb *req, unsigned issue_flags)
        }
        if (def->poll_exclusive)
                mask |= EPOLLEXCLUSIVE;
-       if (!(issue_flags & IO_URING_F_UNLOCKED) &&
-           !list_empty(&ctx->apoll_cache)) {
+       if (req->flags & REQ_F_POLLED) {
+               apoll = req->apoll;
+       } else if (!(issue_flags & IO_URING_F_UNLOCKED) &&
+                  !list_empty(&ctx->apoll_cache)) {
                apoll = list_first_entry(&ctx->apoll_cache, struct async_poll,
                                                poll.wait.entry);
                list_del_init(&apoll->poll.wait.entry);