6.6-stable review patch. If anyone has any objections, please let me know.
------------------
From: Jens Axboe axboe@kernel.dk
Commit f7c9134385331c5ef36252895130aa01a92de907 upstream.
The checking for whether or not io_uring can do a non-blocking read or write attempt is gated on FMODE_NOWAIT. However, if the file is pollable, it's feasible to just check if it's currently in a state in which it can sanely receive or send _some_ data.
This avoids unnecessary io-wq punts, and repeated worthless retries before doing that punt, by assuming that some data can get delivered or received if poll tells us that is true. It also allows multishot reads to properly work with these types of files, enabling a bit of a cleanup of the logic that:
c9d952b9103b ("io_uring/rw: fix cflags posting for single issue multishot read")
had to put in place.
Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- io_uring/rw.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-)
--- a/io_uring/rw.c +++ b/io_uring/rw.c @@ -28,9 +28,19 @@ struct io_rw { rwf_t flags; };
-static inline bool io_file_supports_nowait(struct io_kiocb *req) +static bool io_file_supports_nowait(struct io_kiocb *req, __poll_t mask) { - return req->flags & REQ_F_SUPPORT_NOWAIT; + /* If FMODE_NOWAIT is set for a file, we're golden */ + if (req->flags & REQ_F_SUPPORT_NOWAIT) + return true; + /* No FMODE_NOWAIT, if we can poll, check the status */ + if (io_file_can_poll(req)) { + struct poll_table_struct pt = { ._key = mask }; + + return vfs_poll(req->file, &pt) & mask; + } + /* No FMODE_NOWAIT support, and file isn't pollable. Tough luck. */ + return false; }
#ifdef CONFIG_COMPAT @@ -685,8 +695,8 @@ static int io_rw_init_file(struct io_kio * supports async. Otherwise it's impossible to use O_NONBLOCK files * reliably. If not, or it IOCB_NOWAIT is set, don't retry. */ - if ((kiocb->ki_flags & IOCB_NOWAIT) || - ((file->f_flags & O_NONBLOCK) && !io_file_supports_nowait(req))) + if (kiocb->ki_flags & IOCB_NOWAIT || + ((file->f_flags & O_NONBLOCK && (req->flags & REQ_F_SUPPORT_NOWAIT)))) req->flags |= REQ_F_NOWAIT;
if (ctx->flags & IORING_SETUP_IOPOLL) { @@ -752,7 +762,7 @@ static int __io_read(struct io_kiocb *re
if (force_nonblock) { /* If the file doesn't support async, just async punt */ - if (unlikely(!io_file_supports_nowait(req))) { + if (unlikely(!io_file_supports_nowait(req, EPOLLIN))) { ret = io_setup_async_rw(req, iovec, s, true); return ret ?: -EAGAIN; } @@ -927,7 +937,7 @@ int io_write(struct io_kiocb *req, unsig
if (force_nonblock) { /* If the file doesn't support async, just async punt */ - if (unlikely(!io_file_supports_nowait(req))) + if (unlikely(!io_file_supports_nowait(req, EPOLLOUT))) goto copy_iov;
/* File path supports NOWAIT for non-direct_IO only for block devices. */