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io_uring/rw: allow pollable non-blocking attempts for !FMODE_NOWAIT

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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>
This commit is contained in:
Jens Axboe
2024-10-06 10:40:36 -06:00
committed by Greg Kroah-Hartman
parent 90e11232a6
commit 62d5d980b5
1 changed files with 16 additions and 6 deletions
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22
io_uring/rw.c
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@@ -28,9 +28,19 @@ struct io_rw {
rwf_t flags; 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 #ifdef CONFIG_COMPAT
@@ -685,8 +695,8 @@ static int io_rw_init_file(struct io_kiocb *req, fmode_t mode)
* supports async. Otherwise it's impossible to use O_NONBLOCK files * supports async. Otherwise it's impossible to use O_NONBLOCK files
* reliably. If not, or it IOCB_NOWAIT is set, don't retry. * reliably. If not, or it IOCB_NOWAIT is set, don't retry.
*/ */
if ((kiocb->ki_flags & IOCB_NOWAIT) || if (kiocb->ki_flags & IOCB_NOWAIT ||
((file->f_flags & O_NONBLOCK) && !io_file_supports_nowait(req))) ((file->f_flags & O_NONBLOCK && (req->flags & REQ_F_SUPPORT_NOWAIT))))
req->flags |= REQ_F_NOWAIT; req->flags |= REQ_F_NOWAIT;
if (ctx->flags & IORING_SETUP_IOPOLL) { if (ctx->flags & IORING_SETUP_IOPOLL) {
@@ -752,7 +762,7 @@ static int __io_read(struct io_kiocb *req, unsigned int issue_flags)
if (force_nonblock) { if (force_nonblock) {
/* If the file doesn't support async, just async punt */ /* 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); ret = io_setup_async_rw(req, iovec, s, true);
return ret ?: -EAGAIN; return ret ?: -EAGAIN;
} }
@@ -927,7 +937,7 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags)
if (force_nonblock) { if (force_nonblock) {
/* If the file doesn't support async, just async punt */ /* 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; goto copy_iov;
/* File path supports NOWAIT for non-direct_IO only for block devices. */ /* File path supports NOWAIT for non-direct_IO only for block devices. */