Commit 17a91051 authored by Pavel Begunkov's avatar Pavel Begunkov Committed by Jens Axboe
Browse files

io_uring/io-wq: close io-wq full-stop gap 



There is an old problem with io-wq cancellation where requests should be
killed and are in io-wq but are not discoverable, e.g. in @next_hashed
or @linked vars of io_worker_handle_work(). It adds some unreliability
to individual request canellation, but also may potentially get
__io_uring_cancel() stuck. For instance:

1) An __io_uring_cancel()'s cancellation round have not found any
   request but there are some as desribed.
2) __io_uring_cancel() goes to sleep
3) Then workers wake up and try to execute those hidden requests
   that happen to be unbound.

As we already cancel all requests of io-wq there, set IO_WQ_BIT_EXIT
in advance, so preventing 3) from executing unbound requests. The
workers will initially break looping because of getting a signal as they
are threads of the dying/exec()'ing user task.

Cc: stable@vger.kernel.org
Signed-off-by: default avatarPavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/abfcf8c54cb9e8f7bfbad7e9a0cc5433cc70bdc2.1621781238.git.asml.silence@gmail.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent ba5ef6dc

fs/io-wq.c

+9 −11
Original line number Diff line number Diff line
@@ -979,13 +979,16 @@ static bool io_task_work_match(struct callback_head *cb, void *data) 
	return cwd->wqe->wq == data;

}



void io_wq_exit_start(struct io_wq *wq)

{

	set_bit(IO_WQ_BIT_EXIT, &wq->state);

}



static void io_wq_exit_workers(struct io_wq *wq)

{

	struct callback_head *cb;

	int node;



	set_bit(IO_WQ_BIT_EXIT, &wq->state);



	if (!wq->task)

		return;
@@ -1020,8 +1023,6 @@ static void io_wq_destroy(struct io_wq *wq) 


	cpuhp_state_remove_instance_nocalls(io_wq_online, &wq->cpuhp_node);



	io_wq_exit_workers(wq);



	for_each_node(node) {

		struct io_wqe *wqe = wq->wqes[node];

		struct io_cb_cancel_data match = {
@@ -1036,16 +1037,13 @@ static void io_wq_destroy(struct io_wq *wq) 
	kfree(wq);

}



void io_wq_put(struct io_wq *wq)

{

	if (refcount_dec_and_test(&wq->refs))

		io_wq_destroy(wq);

}



void io_wq_put_and_exit(struct io_wq *wq)

{

	WARN_ON_ONCE(!test_bit(IO_WQ_BIT_EXIT, &wq->state));



	io_wq_exit_workers(wq);

	io_wq_put(wq);

	if (refcount_dec_and_test(&wq->refs))

		io_wq_destroy(wq);

}



static bool io_wq_worker_affinity(struct io_worker *worker, void *data)

fs/io-wq.h

+1 −1
Original line number Diff line number Diff line
@@ -122,7 +122,7 @@ struct io_wq_data { 
};



struct io_wq *io_wq_create(unsigned bounded, struct io_wq_data *data);

void io_wq_put(struct io_wq *wq);

void io_wq_exit_start(struct io_wq *wq);

void io_wq_put_and_exit(struct io_wq *wq);



void io_wq_enqueue(struct io_wq *wq, struct io_wq_work *work);

fs/io_uring.c

+6 −0
Original line number Diff line number Diff line
@@ -9078,6 +9078,9 @@ static void io_uring_cancel_sqpoll(struct io_sq_data *sqd) 


	if (!current->io_uring)

		return;

	if (tctx->io_wq)

		io_wq_exit_start(tctx->io_wq);



	WARN_ON_ONCE(!sqd || sqd->thread != current);



	atomic_inc(&tctx->in_idle);
@@ -9112,6 +9115,9 @@ void __io_uring_cancel(struct files_struct *files) 
	DEFINE_WAIT(wait);

	s64 inflight;



	if (tctx->io_wq)

		io_wq_exit_start(tctx->io_wq);



	/* make sure overflow events are dropped */

	atomic_inc(&tctx->in_idle);

	do {