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io_uring: save ctx put/get for task_work submit

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Do a little trick in io_ring_ctx_free() briefly taking uring_lock, that
will wait for everyone currently holding it, so we can skip pinning ctx
with ctx->refs for __io_req_task_submit(), which is executed and loses
its refs/reqs while holding the lock.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Pavel Begunkov 2021-02-12 03:23:54 +00:00 committed by Jens Axboe
parent 921b9054e0
commit 04fc6c802d
1 changed files with 12 additions and 5 deletions
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17
fs/io_uring.c
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@ -2336,6 +2336,7 @@ static void __io_req_task_submit(struct io_kiocb *req)
{
struct io_ring_ctx *ctx = req->ctx;
/* ctx stays valid until unlock, even if we drop all ours ctx->refs */
mutex_lock(&ctx->uring_lock);
if (!ctx->sqo_dead && !io_sq_thread_acquire_mm_files(ctx, req))
__io_queue_sqe(req);
@ -2347,10 +2348,8 @@ static void __io_req_task_submit(struct io_kiocb *req)
static void io_req_task_submit(struct callback_head *cb)
{
struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
struct io_ring_ctx *ctx = req->ctx;
__io_req_task_submit(req);
percpu_ref_put(&ctx->refs);
}
static void io_req_task_queue(struct io_kiocb *req)
@ -2358,12 +2357,12 @@ static void io_req_task_queue(struct io_kiocb *req)
int ret;
req->task_work.func = io_req_task_submit;
percpu_ref_get(&req->ctx->refs);
ret = io_req_task_work_add(req);
if (unlikely(ret))
if (unlikely(ret)) {
percpu_ref_get(&req->ctx->refs);
io_req_task_work_add_fallback(req, io_req_task_cancel);
}
}
static inline void io_queue_next(struct io_kiocb *req)
{
@ -8707,6 +8706,14 @@ static void io_ring_ctx_free(struct io_ring_ctx *ctx)
{
struct io_submit_state *submit_state = &ctx->submit_state;
/*
* Some may use context even when all refs and requests have been put,
* and they are free to do so while still holding uring_lock, see
* __io_req_task_submit(). Wait for them to finish.
*/
mutex_lock(&ctx->uring_lock);
mutex_unlock(&ctx->uring_lock);
io_finish_async(ctx);
io_sqe_buffers_unregister(ctx);