[PATCH 5.11 09/36] io_uring/io-wq: return 2-step work swap scheme

gregkh
2021-03-10T13:25:13Z

From: Pavel Begunkov <asml.silence@gmail.com>

commit 5280f7e530f71ba85baf90169393196976ad0e52 upstream

Saving one lock/unlock for io-wq is not super important, but adds some
ugliness in the code. More important, atomic decs not turning it to zero
for some archs won't give the right ordering/barriers so the
io_steal_work() may pretty easily get subtly and completely broken.

Return back 2-step io-wq work exchange and clean it up.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/io-wq.c | 16 ++++++----------
fs/io-wq.h | 4 ++--
fs/io_uring.c | 26 ++++----------------------
3 files changed, 12 insertions(+), 34 deletions(-)

--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -555,23 +555,21 @@ get_next:

/* handle a whole dependent link */
do {
- struct io_wq_work *old_work, *next_hashed, *linked;
+ struct io_wq_work *next_hashed, *linked;
unsigned int hash = io_get_work_hash(work);

next_hashed = wq_next_work(work);
io_impersonate_work(worker, work);
+ wq->do_work(work);
+ io_assign_current_work(worker, NULL);

- old_work = work;
- linked = wq->do_work(work);
-
+ linked = wq->free_work(work);
work = next_hashed;
if (!work && linked && !io_wq_is_hashed(linked)) {
work = linked;
linked = NULL;
}
io_assign_current_work(worker, work);
- wq->free_work(old_work);
-
if (linked)
io_wqe_enqueue(wqe, linked);

@@ -850,11 +848,9 @@ static void io_run_cancel(struct io_wq_w
struct io_wq *wq = wqe->wq;

do {
- struct io_wq_work *old_work = work;
-
work->flags |= IO_WQ_WORK_CANCEL;
- work = wq->do_work(work);
- wq->free_work(old_work);
+ wq->do_work(work);
+ work = wq->free_work(work);
} while (work);
}

--- a/fs/io-wq.h
+++ b/fs/io-wq.h
@@ -106,8 +106,8 @@ static inline struct io_wq_work *wq_next
return container_of(work->list.next, struct io_wq_work, list);
}

-typedef void (free_work_fn)(struct io_wq_work *);
-typedef struct io_wq_work *(io_wq_work_fn)(struct io_wq_work *);
+typedef struct io_wq_work *(free_work_fn)(struct io_wq_work *);
+typedef void (io_wq_work_fn)(struct io_wq_work *);

struct io_wq_data {
struct user_struct *user;
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2365,22 +2365,6 @@ static inline void io_put_req_deferred(s
io_free_req_deferred(req);
}

-static struct io_wq_work *io_steal_work(struct io_kiocb *req)
-{
- struct io_kiocb *nxt;
-
- /*
- * A ref is owned by io-wq in which context we're. So, if that's the
- * last one, it's safe to steal next work. False negatives are Ok,
- * it just will be re-punted async in io_put_work()
- */
- if (refcount_read(&req->refs) != 1)
- return NULL;
-
- nxt = io_req_find_next(req);
- return nxt ? &nxt->work : NULL;
-}
-
static void io_double_put_req(struct io_kiocb *req)
{
/* drop both submit and complete references */
@@ -6378,7 +6362,7 @@ static int io_issue_sqe(struct io_kiocb
return 0;
}

-static struct io_wq_work *io_wq_submit_work(struct io_wq_work *work)
+static void io_wq_submit_work(struct io_wq_work *work)
{
struct io_kiocb *req = container_of(work, struct io_kiocb, work);
struct io_kiocb *timeout;
@@ -6429,8 +6413,6 @@ static struct io_wq_work *io_wq_submit_w
if (lock_ctx)
mutex_unlock(&lock_ctx->uring_lock);
}
-
- return io_steal_work(req);
}

static inline struct file *io_file_from_index(struct io_ring_ctx *ctx,
@@ -8062,12 +8044,12 @@ static int io_sqe_files_update(struct io
return __io_sqe_files_update(ctx, &up, nr_args);
}

-static void io_free_work(struct io_wq_work *work)
+static struct io_wq_work *io_free_work(struct io_wq_work *work)
{
struct io_kiocb *req = container_of(work, struct io_kiocb, work);

- /* Consider that io_steal_work() relies on this ref */
- io_put_req(req);
+ req = io_put_req_find_next(req);
+ return req ? &req->work : NULL;
}

static int io_init_wq_offload(struct io_ring_ctx *ctx,