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io_uring: remove redundant memory barrier in io_req_local_work_add

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io_cqring_wake() needs a barrier for the waitqueue_active() check.
However, in the case of io_req_local_work_add(), we call llist_add()
first, which implies an atomic. Hence we can replace smb_mb() with
smp_mb__after_atomic().

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/43983bc8bc507172adda7a0f00cab1aff09fd238.1665018309.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2022-10-06 02:06:10 +01:00 committed by Jens Axboe
parent 3fb1bd6881
commit fc86f9d3bb
2 changed files with 12 additions and 4 deletions
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5
io_uring/io_uring.c
View File

@ -1106,6 +1106,8 @@ static void io_req_local_work_add(struct io_kiocb *req)
if (!llist_add(&req->io_task_work.node, &ctx->work_llist))
return;
/* need it for the following io_cqring_wake() */
smp_mb__after_atomic();
if (unlikely(atomic_read(&req->task->io_uring->in_idle))) {
io_move_task_work_from_local(ctx);
@ -1117,8 +1119,7 @@ static void io_req_local_work_add(struct io_kiocb *req)
if (ctx->has_evfd)
io_eventfd_signal(ctx);
io_cqring_wake(ctx);
__io_cqring_wake(ctx);
}
static inline void __io_req_task_work_add(struct io_kiocb *req, bool allow_local)

11
io_uring/io_uring.h
View File

@ -203,17 +203,24 @@ static inline void io_commit_cqring(struct io_ring_ctx *ctx)
smp_store_release(&ctx->rings->cq.tail, ctx->cached_cq_tail);
}
static inline void io_cqring_wake(struct io_ring_ctx *ctx)
/* requires smb_mb() prior, see wq_has_sleeper() */
static inline void __io_cqring_wake(struct io_ring_ctx *ctx)
{
/*
* wake_up_all() may seem excessive, but io_wake_function() and
* io_should_wake() handle the termination of the loop and only
* wake as many waiters as we need to.
*/
if (wq_has_sleeper(&ctx->cq_wait))
if (waitqueue_active(&ctx->cq_wait))
wake_up_all(&ctx->cq_wait);
}
static inline void io_cqring_wake(struct io_ring_ctx *ctx)
{
smp_mb();
__io_cqring_wake(ctx);
}
static inline bool io_sqring_full(struct io_ring_ctx *ctx)
{
struct io_rings *r = ctx->rings;