io_uring: move reissue into regular IO path

It's non-obvious how retry is done for block backed files, when it happens
off the kiocb done path. It also makes it tricky to deal with the iov_iter
handling.

Just mark the req as needing a reissue, and handling it from the
submission path instead. This makes it directly obvious that we're not
re-importing the iovec from userspace past the submit point, and it means
that we can just reuse our usual -EAGAIN retry path from the read/write
handling.

At some point in the future, we'll gain the ability to always reliably
return -EAGAIN through the stack. A previous attempt on the block side
didn't pan out and got reverted, hence the need to check for this
information out-of-band right now.

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

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 7179424..8be5420 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -697,6 +697,7 @@ enum {
        REQ_F_NO_FILE_TABLE_BIT,
        REQ_F_LTIMEOUT_ACTIVE_BIT,
        REQ_F_COMPLETE_INLINE_BIT,
+       REQ_F_REISSUE_BIT,
 
        /* not a real bit, just to check we're not overflowing the space */
        __REQ_F_LAST_BIT,
@@ -740,6 +741,8 @@ enum {
        REQ_F_LTIMEOUT_ACTIVE   = BIT(REQ_F_LTIMEOUT_ACTIVE_BIT),
        /* completion is deferred through io_comp_state */
        REQ_F_COMPLETE_INLINE   = BIT(REQ_F_COMPLETE_INLINE_BIT),
+       /* caller should reissue async */
+       REQ_F_REISSUE           = BIT(REQ_F_REISSUE_BIT),
 };
 
 struct async_poll {
@@ -2503,8 +2506,10 @@ static void __io_complete_rw(struct io_kiocb *req, long res, long res2,
 
        if (req->rw.kiocb.ki_flags & IOCB_WRITE)
                kiocb_end_write(req);
-       if ((res == -EAGAIN || res == -EOPNOTSUPP) && io_rw_reissue(req))
+       if ((res == -EAGAIN || res == -EOPNOTSUPP) && io_rw_should_reissue(req)) {
+               req->flags |= REQ_F_REISSUE;
                return;
+       }
        if (res != req->result)
                req_set_fail_links(req);
        if (req->flags & REQ_F_BUFFER_SELECTED)
@@ -3283,9 +3288,7 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
 
        ret = io_iter_do_read(req, iter);
 
-       if (ret == -EIOCBQUEUED) {
-               goto out_free;
-       } else if (ret == -EAGAIN) {
+       if (ret == -EAGAIN || (req->flags & REQ_F_REISSUE)) {
                /* IOPOLL retry should happen for io-wq threads */
                if (!force_nonblock && !(req->ctx->flags & IORING_SETUP_IOPOLL))
                        goto done;
@@ -3295,6 +3298,8 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
                /* some cases will consume bytes even on error returns */
                iov_iter_revert(iter, io_size - iov_iter_count(iter));
                ret = 0;
+       } else if (ret == -EIOCBQUEUED) {
+               goto out_free;
        } else if (ret <= 0 || ret == io_size || !force_nonblock ||
                   (req->flags & REQ_F_NOWAIT) || !(req->flags & REQ_F_ISREG)) {
                /* read all, failed, already did sync or don't want to retry */
@@ -3407,6 +3412,9 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
        else
                ret2 = -EINVAL;
 
+       if (req->flags & REQ_F_REISSUE)
+               ret2 = -EAGAIN;
+
        /*
         * Raw bdev writes will return -EOPNOTSUPP for IOCB_NOWAIT. Just
         * retry them without IOCB_NOWAIT.
@@ -6160,6 +6168,7 @@ static void io_wq_submit_work(struct io_wq_work *work)
                ret = -ECANCELED;
 
        if (!ret) {
+               req->flags &= ~REQ_F_REISSUE;
                do {
                        ret = io_issue_sqe(req, 0);
                        /*