io_uring: update kiocb->ki_pos at execution time

Update kiocb->ki_pos at execution time rather than in io_prep_rw().
io_prep_rw() happens before the job is enqueued to a worker and so the
offset might be read multiple times before being executed once.

Ensures that the file position in a set of _linked_ SQEs will be only
obtained after earlier SQEs have completed, and so will include their
incremented file position.

Signed-off-by: Dylan Yudaken <dylany@fb.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index d9c0fd0..d0f3e08 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3020,14 +3020,6 @@ static int io_prep_rw(struct io_kiocb *req, const struct io_uring_sqe *sqe)
                req->flags |= io_file_get_flags(file) << REQ_F_SUPPORT_NOWAIT_BIT;
 
        kiocb->ki_pos = READ_ONCE(sqe->off);
-       if (kiocb->ki_pos == -1) {
-               if (!(file->f_mode & FMODE_STREAM)) {
-                       req->flags |= REQ_F_CUR_POS;
-                       kiocb->ki_pos = file->f_pos;
-               } else {
-                       kiocb->ki_pos = 0;
-               }
-       }
        kiocb->ki_flags = iocb_flags(file);
        ret = kiocb_set_rw_flags(kiocb, READ_ONCE(sqe->rw_flags));
        if (unlikely(ret))
@@ -3094,6 +3086,20 @@ static inline void io_rw_done(struct kiocb *kiocb, ssize_t ret)
        }
 }
 
+static inline void io_kiocb_update_pos(struct io_kiocb *req)
+{
+       struct kiocb *kiocb = &req->rw.kiocb;
+
+       if (kiocb->ki_pos == -1) {
+               if (!(req->file->f_mode & FMODE_STREAM)) {
+                       req->flags |= REQ_F_CUR_POS;
+                       kiocb->ki_pos = req->file->f_pos;
+               } else {
+                       kiocb->ki_pos = 0;
+               }
+       }
+}
+
 static void kiocb_done(struct io_kiocb *req, ssize_t ret,
                       unsigned int issue_flags)
 {
@@ -3682,6 +3688,8 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
                kiocb->ki_flags &= ~IOCB_NOWAIT;
        }
 
+       io_kiocb_update_pos(req);
+
        ret = rw_verify_area(READ, req->file, io_kiocb_ppos(kiocb), req->result);
        if (unlikely(ret)) {
                kfree(iovec);
@@ -3811,6 +3819,8 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
                kiocb->ki_flags &= ~IOCB_NOWAIT;
        }
 
+       io_kiocb_update_pos(req);
+
        ret = rw_verify_area(WRITE, req->file, io_kiocb_ppos(kiocb), req->result);
        if (unlikely(ret))
                goto out_free;