> 2019年10月17日 23:24，Jens Axboe <ax...@kernel.dk> 写道：
>
> We've got two issues with the non-regular file handling for non-blocking
> IO:
>
> 1) We don't want to re-do a short read in full for a non-regular file,
> as we can't just read the data again.
> 2) For non-regular files that don't support non-blocking IO attempts,
> we need to punt to async context even if the file is opened as
> non-blocking. Otherwise the caller always gets -EAGAIN.
>
> Add two new request flags to handle these cases. One is just a cache
> of the inode S_ISREG() status, the other tells io_uring that we always
> need to punt this request to async context, even if REQ_F_NOWAIT is set.
>
> Cc: sta...@vger.kernel.org
> Reported-by: Hrvoje Zeba <zeba.hrv...@gmail.com>
> Signed-off-by: Jens Axboe <ax...@kernel.dk>
> ---
> fs/io_uring.c | 55 +++++++++++++++++++++++++++++++++++----------------
> 1 file changed, 38 insertions(+), 17 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index d2cb277da2f4..a4ee5436cb61 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -322,6 +322,8 @@ struct io_kiocb {
> #define REQ_F_FAIL_LINK 256 /* fail rest of links */
> #define REQ_F_SHADOW_DRAIN 512 /* link-drain shadow req */
> #define REQ_F_TIMEOUT 1024 /* timeout request */
> +#define REQ_F_ISREG 2048 /* regular file */
> +#define REQ_F_MUST_PUNT 4096 /* must be punted even for
> NONBLOCK */
> u64 user_data;
> u32 result;
> u32 sequence;
> @@ -914,26 +916,26 @@ static int io_iopoll_check(struct io_ring_ctx *ctx,
> unsigned *nr_events,
> return ret;
> }
>
> -static void kiocb_end_write(struct kiocb *kiocb)
> +static void kiocb_end_write(struct io_kiocb *req)
> {
> - if (kiocb->ki_flags & IOCB_WRITE) {
> - struct inode *inode = file_inode(kiocb->ki_filp);
> + /*
> + * Tell lockdep we inherited freeze protection from submission
> + * thread.
> + */
> + if (req->flags & REQ_F_ISREG) {
> + struct inode *inode = file_inode(req->file);
>
> - /*
> - * Tell lockdep we inherited freeze protection from submission
> - * thread.
> - */
> - if (S_ISREG(inode->i_mode))
> - __sb_writers_acquired(inode->i_sb, SB_FREEZE_WRITE);
> - file_end_write(kiocb->ki_filp);
> + __sb_writers_acquired(inode->i_sb, SB_FREEZE_WRITE);
> }
> + file_end_write(req->file);
> }
>
> static void io_complete_rw(struct kiocb *kiocb, long res, long res2)
> {
> struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
>
> - kiocb_end_write(kiocb);
> + if (kiocb->ki_flags & IOCB_WRITE)
> + kiocb_end_write(req);
>
> if ((req->flags & REQ_F_LINK) && res != req->result)
> req->flags |= REQ_F_FAIL_LINK;
> @@ -945,7 +947,8 @@ static void io_complete_rw_iopoll(struct kiocb *kiocb,
> long res, long res2)
> {
> struct io_kiocb *req = container_of(kiocb, struct io_kiocb, rw);
>
> - kiocb_end_write(kiocb);
> + if (kiocb->ki_flags & IOCB_WRITE)
> + kiocb_end_write(req);
>
> if ((req->flags & REQ_F_LINK) && res != req->result)
> req->flags |= REQ_F_FAIL_LINK;
> @@ -1059,8 +1062,17 @@ static int io_prep_rw(struct io_kiocb *req, const
> struct sqe_submit *s,
> if (!req->file)
> return -EBADF;
>
> - if (force_nonblock && !io_file_supports_async(req->file))
> + if (S_ISREG(file_inode(req->file)->i_mode))
> + req->flags |= REQ_F_ISREG;
> +
> + /*
> + * If the file doesn't support async, mark it as REQ_F_MUST_PUNT so
> + * we know to async punt it even if it was opened O_NONBLOCK
> + */
> + if (force_nonblock && !io_file_supports_async(req->file)) {
> force_nonblock = false;
> + req->flags |= REQ_F_MUST_PUNT;
> + }
Hello Jens. that is your new version.
+ /*
+ * If the file doesn't support async, mark it as REQ_F_MUST_PUNT so
+ * we know to async punt it even if it was opened O_NONBLOCK
+ */
+ if (force_nonblock && !io_file_supports_async(req->file)) {
+ req->flags |= REQ_F_MUST_PUNT;
+ return -EAGAIN;
+ }
So, if req->file don't support async, we always return EAGAIN immediately.
>
> kiocb->ki_pos = READ_ONCE(sqe->off);
> kiocb->ki_flags = iocb_flags(kiocb->ki_filp);
> @@ -1081,7 +1093,8 @@ static int io_prep_rw(struct io_kiocb *req, const
> struct sqe_submit *s,
> return ret;
>
> /* don't allow async punt if RWF_NOWAIT was requested */
> - if (kiocb->ki_flags & IOCB_NOWAIT)
> + if ((kiocb->ki_flags & IOCB_NOWAIT) ||
> + (req->file->f_flags & O_NONBLOCK))
I think if we return -EAGAIN immediately, and using the work queue to execute
this context,
this is unnecessary.
> req->flags |= REQ_F_NOWAIT;
>
> if (force_nonblock)
> @@ -1382,7 +1395,9 @@ static int io_read(struct io_kiocb *req, const struct
> sqe_submit *s,
> * need async punt anyway, so it's more efficient to do it
> * here.
> */
> - if (force_nonblock && ret2 > 0 && ret2 < read_size)
> + if (force_nonblock && !(req->flags & REQ_F_NOWAIT) &&
> + (req->flags & REQ_F_ISREG) &&
> + ret2 > 0 && ret2 < read_size)
> ret2 = -EAGAIN;
This is also unnecessary because force_nonblock is always false.
--
Jackie Liu
