[PATCH 1/2] io_uring: retain iov_iter state over io_read/io_write calls

Jens Axboe
2020-08-14T19:58:56Z

Instead of maintaining (and setting/remembering) iov_iter size and
segment counts, just put the iov_iter in the async part of the IO
structure.

This is mostly a preparation patch for doing appropriate internal retries
for short reads, but it also cleans up the state handling nicely and
simplifies it quite a bit.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
fs/io_uring.c | 114 ++++++++++++++++++++++++--------------------------
1 file changed, 54 insertions(+), 60 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 1ec25ee71372..409cfa1d6d90 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -508,9 +508,7 @@ struct io_async_msghdr {

struct io_async_rw {
struct iovec fast_iov[UIO_FASTIOV];
- struct iovec *iov;
- ssize_t nr_segs;
- ssize_t size;
+ struct iov_iter iter;
struct wait_page_queue wpq;
};

@@ -915,8 +913,7 @@ static void io_file_put_work(struct work_struct *work);
static ssize_t io_import_iovec(int rw, struct io_kiocb *req,
struct iovec **iovec, struct iov_iter *iter,
bool needs_lock);
-static int io_setup_async_rw(struct io_kiocb *req, ssize_t io_size,
- struct iovec *iovec, struct iovec *fast_iov,
+static int io_setup_async_rw(struct io_kiocb *req, struct iovec *iovec,
struct iov_iter *iter);

static struct kmem_cache *req_cachep;
@@ -2299,7 +2296,7 @@ static bool io_resubmit_prep(struct io_kiocb *req, int error)
ret = io_import_iovec(rw, req, &iovec, &iter, false);
if (ret < 0)
goto end_req;
- ret = io_setup_async_rw(req, ret, iovec, inline_vecs, &iter);
+ ret = io_setup_async_rw(req, iovec, &iter);
if (!ret)
return true;
kfree(iovec);
@@ -2820,6 +2817,13 @@ static ssize_t io_import_iovec(int rw, struct io_kiocb *req,
ssize_t ret;
u8 opcode;

+ if (req->io) {
+ struct io_async_rw *iorw = &req->io->rw;
+
+ *iovec = NULL;
+ return iov_iter_count(&iorw->iter);
+ }
+
opcode = req->opcode;
if (opcode == IORING_OP_READ_FIXED || opcode == IORING_OP_WRITE_FIXED) {
*iovec = NULL;
@@ -2845,14 +2849,6 @@ static ssize_t io_import_iovec(int rw, struct io_kiocb *req,
return ret < 0 ? ret : sqe_len;
}

- if (req->io) {
- struct io_async_rw *iorw = &req->io->rw;
-
- iov_iter_init(iter, rw, iorw->iov, iorw->nr_segs, iorw->size);
- *iovec = NULL;
- return iorw->size;
- }
-
if (req->flags & REQ_F_BUFFER_SELECT) {
ret = io_iov_buffer_select(req, *iovec, needs_lock);
if (!ret) {
@@ -2930,21 +2926,19 @@ static ssize_t loop_rw_iter(int rw, struct file *file, struct kiocb *kiocb,
return ret;
}

-static void io_req_map_rw(struct io_kiocb *req, ssize_t io_size,
- struct iovec *iovec, struct iovec *fast_iov,
+static void io_req_map_rw(struct io_kiocb *req, const struct iovec *iovec,
struct iov_iter *iter)
{
struct io_async_rw *rw = &req->io->rw;

- rw->nr_segs = iter->nr_segs;
- rw->size = io_size;
+ memcpy(&rw->iter, iter, sizeof(*iter));
if (!iovec) {
- rw->iov = rw->fast_iov;
- if (rw->iov != fast_iov)
- memcpy(rw->iov, fast_iov,
+ rw->iter.iov = rw->fast_iov;
+ if (rw->fast_iov != iter->iov)
+ memcpy(rw->fast_iov, iter->iov,
sizeof(struct iovec) * iter->nr_segs);
} else {
- rw->iov = iovec;
+ rw->iter.iov = iovec;
req->flags |= REQ_F_NEED_CLEANUP;
}
}
@@ -2963,8 +2957,7 @@ static int io_alloc_async_ctx(struct io_kiocb *req)
return __io_alloc_async_ctx(req);
}

-static int io_setup_async_rw(struct io_kiocb *req, ssize_t io_size,
- struct iovec *iovec, struct iovec *fast_iov,
+static int io_setup_async_rw(struct io_kiocb *req, struct iovec *iovec,
struct iov_iter *iter)
{
if (!io_op_defs[req->opcode].async_ctx)
@@ -2973,7 +2966,7 @@ static int io_setup_async_rw(struct io_kiocb *req, ssize_t io_size,
if (__io_alloc_async_ctx(req))
return -ENOMEM;

- io_req_map_rw(req, io_size, iovec, fast_iov, iter);
+ io_req_map_rw(req, iovec, iter);
}
return 0;
}
@@ -2981,18 +2974,19 @@ static int io_setup_async_rw(struct io_kiocb *req, ssize_t io_size,
static inline int io_rw_prep_async(struct io_kiocb *req, int rw,
bool force_nonblock)
{
- struct io_async_ctx *io = req->io;
- struct iov_iter iter;
+ struct io_async_rw *iorw = &req->io->rw;
ssize_t ret;

- io->rw.iov = io->rw.fast_iov;
+ iorw->iter.iov = iorw->fast_iov;
+ /* reset ->io around the iovec import, we don't want to use it */
req->io = NULL;
- ret = io_import_iovec(rw, req, &io->rw.iov, &iter, !force_nonblock);
- req->io = io;
+ ret = io_import_iovec(rw, req, (struct iovec **) &iorw->iter.iov,
+ &iorw->iter, !force_nonblock);
+ req->io = container_of(iorw, struct io_async_ctx, rw);
if (unlikely(ret < 0))
return ret;

- io_req_map_rw(req, ret, io->rw.iov, io->rw.fast_iov, &iter);
+ io_req_map_rw(req, iorw->iter.iov, &iorw->iter);
return 0;
}

@@ -3090,7 +3084,8 @@ static inline int kiocb_wait_page_queue_init(struct kiocb *kiocb,
* succeed, or in rare cases where it fails, we then fall back to using the
* async worker threads for a blocking retry.
*/
-static bool io_rw_should_retry(struct io_kiocb *req)
+static bool io_rw_should_retry(struct io_kiocb *req, struct iovec *iovec,
+ struct iovec *fast_iov, struct iov_iter *iter)
{
struct kiocb *kiocb = &req->rw.kiocb;
int ret;
@@ -3113,8 +3108,11 @@ static bool io_rw_should_retry(struct io_kiocb *req)
* If request type doesn't require req->io to defer in general,
* we need to allocate it here
*/
- if (!req->io && __io_alloc_async_ctx(req))
- return false;
+ if (!req->io) {
+ if (__io_alloc_async_ctx(req))
+ return false;
+ io_req_map_rw(req, iovec, iter);
+ }

ret = kiocb_wait_page_queue_init(kiocb, &req->io->rw.wpq,
io_async_buf_func, req);
@@ -3141,12 +3139,14 @@ static int io_read(struct io_kiocb *req, bool force_nonblock,
{
struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
struct kiocb *kiocb = &req->rw.kiocb;
- struct iov_iter iter;
+ struct iov_iter __iter, *iter = &__iter;
size_t iov_count;
- ssize_t io_size, ret, ret2;
- unsigned long nr_segs;
+ ssize_t io_size, ret, ret2 = 0;
+
+ if (req->io)
+ iter = &req->io->rw.iter;

- ret = io_import_iovec(READ, req, &iovec, &iter, !force_nonblock);
+ ret = io_import_iovec(READ, req, &iovec, iter, !force_nonblock);
if (ret < 0)
return ret;
io_size = ret;
@@ -3160,30 +3160,26 @@ static int io_read(struct io_kiocb *req, bool force_nonblock,
if (force_nonblock && !io_file_supports_async(req->file, READ))
goto copy_iov;

- iov_count = iov_iter_count(&iter);
- nr_segs = iter.nr_segs;
+ iov_count = iov_iter_count(iter);
ret = rw_verify_area(READ, req->file, &kiocb->ki_pos, iov_count);
if (unlikely(ret))
goto out_free;

- ret2 = io_iter_do_read(req, &iter);
+ ret2 = io_iter_do_read(req, iter);

/* Catch -EAGAIN return for forced non-blocking submission */
if (!force_nonblock || (ret2 != -EAGAIN && ret2 != -EIO)) {
kiocb_done(kiocb, ret2, cs);
} else {
- iter.count = iov_count;
- iter.nr_segs = nr_segs;
copy_iov:
- ret = io_setup_async_rw(req, io_size, iovec, inline_vecs,
- &iter);
+ ret = io_setup_async_rw(req, iovec, iter);
if (ret)
goto out_free;
/* it's copied and will be cleaned with ->io */
iovec = NULL;
/* if we can retry, do so with the callbacks armed */
- if (io_rw_should_retry(req)) {
- ret2 = io_iter_do_read(req, &iter);
+ if (io_rw_should_retry(req, iovec, inline_vecs, iter)) {
+ ret2 = io_iter_do_read(req, iter);
if (ret2 == -EIOCBQUEUED) {
goto out_free;
} else if (ret2 != -EAGAIN) {
@@ -3223,12 +3219,14 @@ static int io_write(struct io_kiocb *req, bool force_nonblock,
{
struct iovec inline_vecs[UIO_FASTIOV], *iovec = inline_vecs;
struct kiocb *kiocb = &req->rw.kiocb;
- struct iov_iter iter;
+ struct iov_iter __iter, *iter = &__iter;
size_t iov_count;
ssize_t ret, ret2, io_size;
- unsigned long nr_segs;

- ret = io_import_iovec(WRITE, req, &iovec, &iter, !force_nonblock);
+ if (req->io)
+ iter = &req->io->rw.iter;
+
+ ret = io_import_iovec(WRITE, req, &iovec, iter, !force_nonblock);
if (ret < 0)
return ret;
io_size = ret;
@@ -3247,8 +3245,7 @@ static int io_write(struct io_kiocb *req, bool force_nonblock,
(req->flags & REQ_F_ISREG))
goto copy_iov;

- iov_count = iov_iter_count(&iter);
- nr_segs = iter.nr_segs;
+ iov_count = iov_iter_count(iter);
ret = rw_verify_area(WRITE, req->file, &kiocb->ki_pos, iov_count);
if (unlikely(ret))
goto out_free;
@@ -3269,9 +3266,9 @@ static int io_write(struct io_kiocb *req, bool force_nonblock,
kiocb->ki_flags |= IOCB_WRITE;

if (req->file->f_op->write_iter)
- ret2 = call_write_iter(req->file, kiocb, &iter);
+ ret2 = call_write_iter(req->file, kiocb, iter);
else if (req->file->f_op->write)
- ret2 = loop_rw_iter(WRITE, req->file, kiocb, &iter);
+ ret2 = loop_rw_iter(WRITE, req->file, kiocb, iter);
else
ret2 = -EINVAL;

@@ -3284,11 +3281,8 @@ static int io_write(struct io_kiocb *req, bool force_nonblock,
if (!force_nonblock || ret2 != -EAGAIN) {
kiocb_done(kiocb, ret2, cs);
} else {
- iter.count = iov_count;
- iter.nr_segs = nr_segs;
copy_iov:
- ret = io_setup_async_rw(req, io_size, iovec, inline_vecs,
- &iter);
+ ret = io_setup_async_rw(req, iovec, iter);
if (ret)
goto out_free;
/* it's copied and will be cleaned with ->io */
@@ -5583,8 +5577,8 @@ static void __io_clean_op(struct io_kiocb *req)
case IORING_OP_WRITEV:
case IORING_OP_WRITE_FIXED:
case IORING_OP_WRITE:
- if (io->rw.iov != io->rw.fast_iov)
- kfree(io->rw.iov);
+ if (io->rw.iter.iov != io->rw.fast_iov)
+ kfree(io->rw.iter.iov);
break;
case IORING_OP_RECVMSG:
case IORING_OP_SENDMSG:
--
2.28.0