io_uring/rw: don't allow multishot reads without NOWAIT support

Supporting multishot reads requires support for NOWAIT, as the
alternative would be always having io-wq execute the work item whenever
the poll readiness triggered. Any fast file type will have NOWAIT
support (eg it understands both O_NONBLOCK and IOCB_NOWAIT). If the
given file type does not, then simply resort to single shot execution.

Cc: stable@vger.kernel.org
Fixes: fc68fcda04910 ("io_uring/rw: add support for IORING_OP_READ_MULTISHOT")
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/io_uring/rw.c b/io_uring/rw.c
index 0585ebcc9773d3349b007e6ff436c0320e26356d..c8d48287439e5a06d19113ecb07f1c05db47dc3f 100644 (file)
--- a/io_uring/rw.c
+++ b/io_uring/rw.c
@@ -936,6 +936,13 @@ int io_read_mshot(struct io_kiocb *req, unsigned int issue_flags)
 
        ret = __io_read(req, issue_flags);
 
+       /*
+        * If the file doesn't support proper NOWAIT, then disable multishot
+        * and stay in single shot mode.
+        */
+       if (!io_file_supports_nowait(req))
+               req->flags &= ~REQ_F_APOLL_MULTISHOT;
+
        /*
         * If we get -EAGAIN, recycle our buffer and just let normal poll
         * handling arm it.
@@ -955,7 +962,7 @@ int io_read_mshot(struct io_kiocb *req, unsigned int issue_flags)
        /*
         * Any successful return value will keep the multishot read armed.
         */
-       if (ret > 0) {
+       if (ret > 0 && req->flags & REQ_F_APOLL_MULTISHOT) {
                /*
                 * Put our buffer and post a CQE. If we fail to post a CQE, then
                 * jump to the termination path. This request is then done.