io_uring: fix handling SQEs requesting NOWAIT [Linux 5.1]

io_uring: fix handling SQEs requesting NOWAIT [Linux 5.1]

This Linux kernel change "io_uring: fix handling SQEs requesting NOWAIT" is included in the Linux 5.1 release. This change is authored by Stefan Bühler <source [at] stbuehler.de> on Sat Apr 27 20:34:19 2019 +0200. The commit for this change in Linux stable tree is 8449eed (patch).

io_uring: fix handling SQEs requesting NOWAIT

Not all request types set REQ_F_FORCE_NONBLOCK when they needed async
punting; reverse logic instead and set REQ_F_NOWAIT if request mustn't
be punted.

Signed-off-by: Stefan Bühler <[email protected]>

Merged with my previous patch for this.

Signed-off-by: Jens Axboe <[email protected]>

There are 17 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 fs/io_uring.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 0e9fb2c..d5e23a6 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -221,7 +221,7 @@ struct io_kiocb {
    struct list_head    list;
    unsigned int        flags;
    refcount_t      refs;
-#define REQ_F_FORCE_NONBLOCK   1   /* inline submission attempt */
+#define REQ_F_NOWAIT       1   /* must not punt to workers */
 #define REQ_F_IOPOLL_COMPLETED 2   /* polled IO has completed */
 #define REQ_F_FIXED_FILE   4   /* ctx owns file */
 #define REQ_F_SEQ_PREV     8   /* sequential with previous */
@@ -774,10 +774,14 @@ static int io_prep_rw(struct io_kiocb *req, const struct sqe_submit *s,
    ret = kiocb_set_rw_flags(kiocb, READ_ONCE(sqe->rw_flags));
    if (unlikely(ret))
        return ret;
-   if (force_nonblock) {
+
+   /* don't allow async punt if RWF_NOWAIT was requested */
+   if (kiocb->ki_flags & IOCB_NOWAIT)
+       req->flags |= REQ_F_NOWAIT;
+
+   if (force_nonblock)
        kiocb->ki_flags |= IOCB_NOWAIT;
-       req->flags |= REQ_F_FORCE_NONBLOCK;
-   }
+
    if (ctx->flags & IORING_SETUP_IOPOLL) {
        if (!(kiocb->ki_flags & IOCB_DIRECT) ||
            !kiocb->ki_filp->f_op->iopoll)
@@ -1436,8 +1440,7 @@ static void io_sq_wq_submit_work(struct work_struct *work)
        struct sqe_submit *s = &req->submit;
        const struct io_uring_sqe *sqe = s->sqe;

-       /* Ensure we clear previously set forced non-block flag */
-       req->flags &= ~REQ_F_FORCE_NONBLOCK;
+       /* Ensure we clear previously set non-block flag */
        req->rw.ki_flags &= ~IOCB_NOWAIT;

        ret = 0;
@@ -1623,7 +1626,7 @@ static int io_submit_sqe(struct io_ring_ctx *ctx, struct sqe_submit *s,
        goto out;

    ret = __io_submit_sqe(ctx, req, s, true);
-   if (ret == -EAGAIN) {
+   if (ret == -EAGAIN && !(req->flags & REQ_F_NOWAIT)) {
        struct io_uring_sqe *sqe_copy;

        sqe_copy = kmalloc(sizeof(*sqe_copy), GFP_KERNEL);

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