Commit 9d8426a0 authored by Jens Axboe's avatar Jens Axboe
Browse files

io_uring: acquire 'mm' for task_work for SQPOLL 



If we're unlucky with timing, we could be running task_work after
having dropped the memory context in the sq thread. Since dropping
the context requires a runnable task state, we cannot reliably drop
it as part of our check-for-work loop in io_sq_thread(). Instead,
abstract out the mm acquire for the sq thread into a helper, and call
it from the async task work handler.

Cc: stable@vger.kernel.org # v5.7
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent bbde017a

fs/io_uring.c

+29 −15
Original line number Diff line number Diff line
@@ -4256,6 +4256,28 @@ static void io_async_queue_proc(struct file *file, struct wait_queue_head *head, 
	__io_queue_proc(&pt->req->apoll->poll, pt, head);

}



static void io_sq_thread_drop_mm(struct io_ring_ctx *ctx)

{

	struct mm_struct *mm = current->mm;



	if (mm) {

		kthread_unuse_mm(mm);

		mmput(mm);

	}

}



static int io_sq_thread_acquire_mm(struct io_ring_ctx *ctx,

				   struct io_kiocb *req)

{

	if (io_op_defs[req->opcode].needs_mm && !current->mm) {

		if (unlikely(!mmget_not_zero(ctx->sqo_mm)))

			return -EFAULT;

		kthread_use_mm(ctx->sqo_mm);

	}



	return 0;

}



static void io_async_task_func(struct callback_head *cb)

{

	struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work);
@@ -4290,11 +4312,16 @@ static void io_async_task_func(struct callback_head *cb) 


	if (!canceled) {

		__set_current_state(TASK_RUNNING);

		if (io_sq_thread_acquire_mm(ctx, req)) {

			io_cqring_add_event(req, -EFAULT);

			goto end_req;

		}

		mutex_lock(&ctx->uring_lock);

		__io_queue_sqe(req, NULL);

		mutex_unlock(&ctx->uring_lock);

	} else {

		io_cqring_ev_posted(ctx);

end_req:

		req_set_fail_links(req);

		io_double_put_req(req);

	}
@@ -5841,11 +5868,8 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req, 
	if (unlikely(req->opcode >= IORING_OP_LAST))

		return -EINVAL;



	if (io_op_defs[req->opcode].needs_mm && !current->mm) {

		if (unlikely(!mmget_not_zero(ctx->sqo_mm)))

	if (unlikely(io_sq_thread_acquire_mm(ctx, req)))

		return -EFAULT;

		kthread_use_mm(ctx->sqo_mm);

	}



	sqe_flags = READ_ONCE(sqe->flags);

	/* enforce forwards compatibility on users */
@@ -5954,16 +5978,6 @@ fail_req: 
	return submitted;

}



static inline void io_sq_thread_drop_mm(struct io_ring_ctx *ctx)

{

	struct mm_struct *mm = current->mm;



	if (mm) {

		kthread_unuse_mm(mm);

		mmput(mm);

	}

}



static int io_sq_thread(void *data)

{

	struct io_ring_ctx *ctx = data;

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