2022-02-21 17:42:40

by Dylan Yudaken

Subject: [PATCH v2 2/4] 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 <[email protected]>
---
fs/io_uring.c | 25 +++++++++++++++++--------
1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 1f9b4466c269..50b93ff2ee12 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -3000,14 +3000,6 @@ 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))
@@ -3074,6 +3066,19 @@ 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)
+{
+ 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)
{
@@ -3662,6 +3667,8 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
kiocb->ki_flags &= ~IOCB_NOWAIT;
}

+ io_kiocb_update_pos(req, kiocb);
+
ret = rw_verify_area(READ, req->file, io_kiocb_ppos(kiocb), req->result);
if (unlikely(ret)) {
kfree(iovec);
@@ -3791,6 +3798,8 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
kiocb->ki_flags &= ~IOCB_NOWAIT;
}

+ io_kiocb_update_pos(req, kiocb);
+
ret = rw_verify_area(WRITE, req->file, io_kiocb_ppos(kiocb), req->result);
if (unlikely(ret))
goto out_free;
--
2.30.2

2022-02-22 01:17:27

by Jens Axboe

Subject: Re: [PATCH v2 2/4] io_uring: update kiocb->ki_pos at execution time

On 2/21/22 7:16 AM, Dylan Yudaken wrote:
> 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 <[email protected]>
> ---
> fs/io_uring.c | 25 +++++++++++++++++--------
> 1 file changed, 17 insertions(+), 8 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 1f9b4466c269..50b93ff2ee12 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -3000,14 +3000,6 @@ 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))
> @@ -3074,6 +3066,19 @@ 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)
> +{
> + 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 inline void io_kiocb_update_pos(struct io_kiocb *req,
struct kiocb *kiocb)
{
}

Can we just drop the kiocb argument? It'll always be req->rw.kiocb.
Should generate the same code if you do:

static inline void io_kiocb_update_pos(struct io_kiocb *req)
{
struct kiocb *kiocb = &req->rw.kiocb;

...
}

Apart from that minor thing, looks good to me.

--
Jens Axboe