io_uring/sqpoll.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Contains the core associated with submission side polling of the SQ
  * ring, offloading submissions from the application to a kernel thread.
  */
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/file.h>
 #include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/audit.h>
 #include <linux/security.h>
 #include <linux/io_uring.h>

 #include <uapi/linux/io_uring.h>

 #include "io_uring.h"
 #include "sqpoll.h"

 #define IORING_SQPOLL_CAP_ENTRIES_VALUE 8

 enum {
 	IO_SQ_THREAD_SHOULD_STOP = 0,
 	IO_SQ_THREAD_SHOULD_PARK,
 };

 void io_sq_thread_unpark(struct io_sq_data *sqd)
 	__releases(&sqd->lock)
 {
 	WARN_ON_ONCE(sqd->thread == current);

 	/*
 	 * Do the dance but not conditional clear_bit() because it'd race with
 	 * other threads incrementing park_pending and setting the bit.
 	 */
 	clear_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state);
 	if (atomic_dec_return(&sqd->park_pending))
 		set_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state);
 	mutex_unlock(&sqd->lock);
 }

 void io_sq_thread_park(struct io_sq_data *sqd)
 	__acquires(&sqd->lock)
 {
 	WARN_ON_ONCE(sqd->thread == current);

 	atomic_inc(&sqd->park_pending);
 	set_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state);
 	mutex_lock(&sqd->lock);
 	if (sqd->thread)
 		wake_up_process(sqd->thread);
 }

 void io_sq_thread_stop(struct io_sq_data *sqd)
 {
 	WARN_ON_ONCE(sqd->thread == current);
 	WARN_ON_ONCE(test_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state));

 	set_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state);
 	mutex_lock(&sqd->lock);
 	if (sqd->thread)
 		wake_up_process(sqd->thread);
 	mutex_unlock(&sqd->lock);
 	wait_for_completion(&sqd->exited);
 }

 void io_put_sq_data(struct io_sq_data *sqd)
 {
 	if (refcount_dec_and_test(&sqd->refs)) {
 		WARN_ON_ONCE(atomic_read(&sqd->park_pending));

 		io_sq_thread_stop(sqd);
 		kfree(sqd);
 	}
 }

 static __cold void io_sqd_update_thread_idle(struct io_sq_data *sqd)
 {
 	struct io_ring_ctx *ctx;
 	unsigned sq_thread_idle = 0;

 	list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
 		sq_thread_idle = max(sq_thread_idle, ctx->sq_thread_idle);
 	sqd->sq_thread_idle = sq_thread_idle;
 }

 void io_sq_thread_finish(struct io_ring_ctx *ctx)
 {
 	struct io_sq_data *sqd = ctx->sq_data;

 	if (sqd) {
 		io_sq_thread_park(sqd);
 		list_del_init(&ctx->sqd_list);
 		io_sqd_update_thread_idle(sqd);
 		io_sq_thread_unpark(sqd);

 		io_put_sq_data(sqd);
 		ctx->sq_data = NULL;
 	}
 }

 static struct io_sq_data *io_attach_sq_data(struct io_uring_params *p)
 {
 	struct io_ring_ctx *ctx_attach;
 	struct io_sq_data *sqd;
 	struct fd f;

 	f = fdget(p->wq_fd);
 	if (!f.file)
 		return ERR_PTR(-ENXIO);
 	if (!io_is_uring_fops(f.file)) {
 		fdput(f);
 		return ERR_PTR(-EINVAL);
 	}

 	ctx_attach = f.file->private_data;
 	sqd = ctx_attach->sq_data;
 	if (!sqd) {
 		fdput(f);
 		return ERR_PTR(-EINVAL);
 	}
 	if (sqd->task_tgid != current->tgid) {
 		fdput(f);
 		return ERR_PTR(-EPERM);
 	}

 	refcount_inc(&sqd->refs);
 	fdput(f);
 	return sqd;
 }

 static struct io_sq_data *io_get_sq_data(struct io_uring_params *p,
 					 bool *attached)
 {
 	struct io_sq_data *sqd;

 	*attached = false;
 	if (p->flags & IORING_SETUP_ATTACH_WQ) {
 		sqd = io_attach_sq_data(p);
 		if (!IS_ERR(sqd)) {
 			*attached = true;
 			return sqd;
 		}
 		/* fall through for EPERM case, setup new sqd/task */
 		if (PTR_ERR(sqd) != -EPERM)
 			return sqd;
 	}

 	sqd = kzalloc(sizeof(*sqd), GFP_KERNEL);
 	if (!sqd)
 		return ERR_PTR(-ENOMEM);

 	atomic_set(&sqd->park_pending, 0);
 	refcount_set(&sqd->refs, 1);
 	INIT_LIST_HEAD(&sqd->ctx_list);
 	mutex_init(&sqd->lock);
 	init_waitqueue_head(&sqd->wait);
 	init_completion(&sqd->exited);
 	return sqd;
 }

 static inline bool io_sqd_events_pending(struct io_sq_data *sqd)
 {
 	return READ_ONCE(sqd->state);
 }

 static int __io_sq_thread(struct io_ring_ctx *ctx, bool cap_entries)
 {
 	unsigned int to_submit;
 	int ret = 0;

 	to_submit = io_sqring_entries(ctx);
 	/* if we're handling multiple rings, cap submit size for fairness */
 	if (cap_entries && to_submit > IORING_SQPOLL_CAP_ENTRIES_VALUE)
 		to_submit = IORING_SQPOLL_CAP_ENTRIES_VALUE;

 	if (!wq_list_empty(&ctx->iopoll_list) || to_submit) {
 		const struct cred *creds = NULL;

 		if (ctx->sq_creds != current_cred())
 			creds = override_creds(ctx->sq_creds);

 		mutex_lock(&ctx->uring_lock);
 		if (!wq_list_empty(&ctx->iopoll_list))
 			io_do_iopoll(ctx, true);

 		/*
 		 * Don't submit if refs are dying, good for io_uring_register(),
 		 * but also it is relied upon by io_ring_exit_work()
 		 */
 		if (to_submit && likely(!percpu_ref_is_dying(&ctx->refs)) &&
 		    !(ctx->flags & IORING_SETUP_R_DISABLED))
 			ret = io_submit_sqes(ctx, to_submit);
 		mutex_unlock(&ctx->uring_lock);

 		if (to_submit && wq_has_sleeper(&ctx->sqo_sq_wait))
 			wake_up(&ctx->sqo_sq_wait);
 		if (creds)
 			revert_creds(creds);
 	}

 	return ret;
 }

 static bool io_sqd_handle_event(struct io_sq_data *sqd)
 {
 	bool did_sig = false;
 	struct ksignal ksig;

 	if (test_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state) ||
 	    signal_pending(current)) {
 		mutex_unlock(&sqd->lock);
 		if (signal_pending(current))
 			did_sig = get_signal(&ksig);
 		cond_resched();
 		mutex_lock(&sqd->lock);
 	}
 	return did_sig || test_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state);
 }

 static int io_sq_thread(void *data)
 {
 	struct io_sq_data *sqd = data;
 	struct io_ring_ctx *ctx;
 	unsigned long timeout = 0;
 	char buf[TASK_COMM_LEN];
 	DEFINE_WAIT(wait);

 	snprintf(buf, sizeof(buf), "iou-sqp-%d", sqd->task_pid);
 	set_task_comm(current, buf);

 	if (sqd->sq_cpu != -1)
 		set_cpus_allowed_ptr(current, cpumask_of(sqd->sq_cpu));
 	else
 		set_cpus_allowed_ptr(current, cpu_online_mask);
 	current->flags |= PF_NO_SETAFFINITY;

 	mutex_lock(&sqd->lock);
 	while (1) {
 		bool cap_entries, sqt_spin = false;

 		if (io_sqd_events_pending(sqd) || signal_pending(current)) {
 			if (io_sqd_handle_event(sqd))
 				break;
 			timeout = jiffies + sqd->sq_thread_idle;
 		}

 		cap_entries = !list_is_singular(&sqd->ctx_list);
 		list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
 			int ret = __io_sq_thread(ctx, cap_entries);

 			if (!sqt_spin && (ret > 0 || !wq_list_empty(&ctx->iopoll_list)))
 				sqt_spin = true;
 		}
 		if (io_run_task_work())
 			sqt_spin = true;

 		if (sqt_spin || !time_after(jiffies, timeout)) {
 			cond_resched();
 			if (sqt_spin)
 				timeout = jiffies + sqd->sq_thread_idle;
 			continue;
 		}

 		prepare_to_wait(&sqd->wait, &wait, TASK_INTERRUPTIBLE);
 		if (!io_sqd_events_pending(sqd) && !task_work_pending(current)) {
 			bool needs_sched = true;

 			list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
 				atomic_or(IORING_SQ_NEED_WAKEUP,
 						&ctx->rings->sq_flags);
 				if ((ctx->flags & IORING_SETUP_IOPOLL) &&
 				    !wq_list_empty(&ctx->iopoll_list)) {
 					needs_sched = false;
 					break;
 				}

 				/*
 				 * Ensure the store of the wakeup flag is not
 				 * reordered with the load of the SQ tail
 				 */
 				smp_mb__after_atomic();

 				if (io_sqring_entries(ctx)) {
 					needs_sched = false;
 					break;
 				}
 			}

 			if (needs_sched) {
 				mutex_unlock(&sqd->lock);
 				schedule();
 				mutex_lock(&sqd->lock);
 			}
 			list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
 				atomic_andnot(IORING_SQ_NEED_WAKEUP,
 						&ctx->rings->sq_flags);
 		}

 		finish_wait(&sqd->wait, &wait);
 		timeout = jiffies + sqd->sq_thread_idle;
 	}

 	io_uring_cancel_generic(true, sqd);
 	sqd->thread = NULL;
 	list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
 		atomic_or(IORING_SQ_NEED_WAKEUP, &ctx->rings->sq_flags);
 	io_run_task_work();
 	mutex_unlock(&sqd->lock);

 	complete(&sqd->exited);
 	do_exit(0);
 }

 int io_sqpoll_wait_sq(struct io_ring_ctx *ctx)
 {
 	DEFINE_WAIT(wait);

 	do {
 		if (!io_sqring_full(ctx))
 			break;
 		prepare_to_wait(&ctx->sqo_sq_wait, &wait, TASK_INTERRUPTIBLE);

 		if (!io_sqring_full(ctx))
 			break;
 		schedule();
 	} while (!signal_pending(current));

 	finish_wait(&ctx->sqo_sq_wait, &wait);
 	return 0;
 }

 __cold int io_sq_offload_create(struct io_ring_ctx *ctx,
 				struct io_uring_params *p)
 {
 	int ret;

 	/* Retain compatibility with failing for an invalid attach attempt */
 	if ((ctx->flags & (IORING_SETUP_ATTACH_WQ | IORING_SETUP_SQPOLL)) ==
 				IORING_SETUP_ATTACH_WQ) {
 		struct fd f;

 		f = fdget(p->wq_fd);
 		if (!f.file)
 			return -ENXIO;
 		if (!io_is_uring_fops(f.file)) {
 			fdput(f);
 			return -EINVAL;
 		}
 		fdput(f);
 	}
 	if (ctx->flags & IORING_SETUP_SQPOLL) {
 		struct task_struct *tsk;
 		struct io_sq_data *sqd;
 		bool attached;

 		ret = security_uring_sqpoll();
 		if (ret)
 			return ret;

 		sqd = io_get_sq_data(p, &attached);
 		if (IS_ERR(sqd)) {
 			ret = PTR_ERR(sqd);
 			goto err;
 		}

 		ctx->sq_creds = get_current_cred();
 		ctx->sq_data = sqd;
 		ctx->sq_thread_idle = msecs_to_jiffies(p->sq_thread_idle);
 		if (!ctx->sq_thread_idle)
 			ctx->sq_thread_idle = HZ;

 		io_sq_thread_park(sqd);
 		list_add(&ctx->sqd_list, &sqd->ctx_list);
 		io_sqd_update_thread_idle(sqd);
 		/* don't attach to a dying SQPOLL thread, would be racy */
 		ret = (attached && !sqd->thread) ? -ENXIO : 0;
 		io_sq_thread_unpark(sqd);

 		if (ret < 0)
 			goto err;
 		if (attached)
 			return 0;

 		if (p->flags & IORING_SETUP_SQ_AFF) {
 			int cpu = p->sq_thread_cpu;

 			ret = -EINVAL;
 			if (cpu >= nr_cpu_ids || !cpu_online(cpu))
 				goto err_sqpoll;
 			sqd->sq_cpu = cpu;
 		} else {
 			sqd->sq_cpu = -1;
 		}

 		sqd->task_pid = current->pid;
 		sqd->task_tgid = current->tgid;
 		tsk = create_io_thread(io_sq_thread, sqd, NUMA_NO_NODE);
 		if (IS_ERR(tsk)) {
 			ret = PTR_ERR(tsk);
 			goto err_sqpoll;
 		}

 		sqd->thread = tsk;
 		ret = io_uring_alloc_task_context(tsk, ctx);
 		wake_up_new_task(tsk);
 		if (ret)
 			goto err;
 	} else if (p->flags & IORING_SETUP_SQ_AFF) {
 		/* Can't have SQ_AFF without SQPOLL */
 		ret = -EINVAL;
 		goto err;
 	}

 	return 0;
 err_sqpoll:
 	complete(&ctx->sq_data->exited);
 err:
 	io_sq_thread_finish(ctx);
 	return ret;
 }
	// SPDX-License-Identifier: GPL-2.0
	/*
	* Contains the core associated with submission side polling of the SQ
	* ring, offloading submissions from the application to a kernel thread.
	*/
	#include <linux/kernel.h>
	#include <linux/errno.h>
	#include <linux/file.h>
	#include <linux/mm.h>
	#include <linux/slab.h>
	#include <linux/audit.h>
	#include <linux/security.h>
	#include <linux/io_uring.h>

	#include <uapi/linux/io_uring.h>

	#include "io_uring.h"
	#include "sqpoll.h"

	#define IORING_SQPOLL_CAP_ENTRIES_VALUE 8

	enum {
	IO_SQ_THREAD_SHOULD_STOP = 0,
	IO_SQ_THREAD_SHOULD_PARK,
	};

	void io_sq_thread_unpark(struct io_sq_data *sqd)
	__releases(&sqd->lock)
	{
	WARN_ON_ONCE(sqd->thread == current);

	/*
	* Do the dance but not conditional clear_bit() because it'd race with
	* other threads incrementing park_pending and setting the bit.
	*/
	clear_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state);
	if (atomic_dec_return(&sqd->park_pending))
	set_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state);
	mutex_unlock(&sqd->lock);
	}

	void io_sq_thread_park(struct io_sq_data *sqd)
	__acquires(&sqd->lock)
	{
	WARN_ON_ONCE(sqd->thread == current);

	atomic_inc(&sqd->park_pending);
	set_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state);
	mutex_lock(&sqd->lock);
	if (sqd->thread)
	wake_up_process(sqd->thread);
	}

	void io_sq_thread_stop(struct io_sq_data *sqd)
	{
	WARN_ON_ONCE(sqd->thread == current);
	WARN_ON_ONCE(test_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state));

	set_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state);
	mutex_lock(&sqd->lock);
	if (sqd->thread)
	wake_up_process(sqd->thread);
	mutex_unlock(&sqd->lock);
	wait_for_completion(&sqd->exited);
	}

	void io_put_sq_data(struct io_sq_data *sqd)
	{
	if (refcount_dec_and_test(&sqd->refs)) {
	WARN_ON_ONCE(atomic_read(&sqd->park_pending));

	io_sq_thread_stop(sqd);
	kfree(sqd);
	}
	}

	static __cold void io_sqd_update_thread_idle(struct io_sq_data *sqd)
	{
	struct io_ring_ctx *ctx;
	unsigned sq_thread_idle = 0;

	list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
	sq_thread_idle = max(sq_thread_idle, ctx->sq_thread_idle);
	sqd->sq_thread_idle = sq_thread_idle;
	}

	void io_sq_thread_finish(struct io_ring_ctx *ctx)
	{
	struct io_sq_data *sqd = ctx->sq_data;

	if (sqd) {
	io_sq_thread_park(sqd);
	list_del_init(&ctx->sqd_list);
	io_sqd_update_thread_idle(sqd);
	io_sq_thread_unpark(sqd);

	io_put_sq_data(sqd);
	ctx->sq_data = NULL;
	}
	}

	static struct io_sq_data io_attach_sq_data(struct io_uring_params p)
	{
	struct io_ring_ctx *ctx_attach;
	struct io_sq_data *sqd;
	struct fd f;

	f = fdget(p->wq_fd);
	if (!f.file)
	return ERR_PTR(-ENXIO);
	if (!io_is_uring_fops(f.file)) {
	fdput(f);
	return ERR_PTR(-EINVAL);
	}

	ctx_attach = f.file->private_data;
	sqd = ctx_attach->sq_data;
	if (!sqd) {
	fdput(f);
	return ERR_PTR(-EINVAL);
	}
	if (sqd->task_tgid != current->tgid) {
	fdput(f);
	return ERR_PTR(-EPERM);
	}

	refcount_inc(&sqd->refs);
	fdput(f);
	return sqd;
	}

	static struct io_sq_data io_get_sq_data(struct io_uring_params p,
	bool *attached)
	{
	struct io_sq_data *sqd;

	*attached = false;
	if (p->flags & IORING_SETUP_ATTACH_WQ) {
	sqd = io_attach_sq_data(p);
	if (!IS_ERR(sqd)) {
	*attached = true;
	return sqd;
	}
	/* fall through for EPERM case, setup new sqd/task */
	if (PTR_ERR(sqd) != -EPERM)
	return sqd;
	}

	sqd = kzalloc(sizeof(*sqd), GFP_KERNEL);
	if (!sqd)
	return ERR_PTR(-ENOMEM);

	atomic_set(&sqd->park_pending, 0);
	refcount_set(&sqd->refs, 1);
	INIT_LIST_HEAD(&sqd->ctx_list);
	mutex_init(&sqd->lock);
	init_waitqueue_head(&sqd->wait);
	init_completion(&sqd->exited);
	return sqd;
	}

	static inline bool io_sqd_events_pending(struct io_sq_data *sqd)
	{
	return READ_ONCE(sqd->state);
	}

	static int __io_sq_thread(struct io_ring_ctx *ctx, bool cap_entries)
	{
	unsigned int to_submit;
	int ret = 0;

	to_submit = io_sqring_entries(ctx);
	/* if we're handling multiple rings, cap submit size for fairness */
	if (cap_entries && to_submit > IORING_SQPOLL_CAP_ENTRIES_VALUE)
	to_submit = IORING_SQPOLL_CAP_ENTRIES_VALUE;

	if (!wq_list_empty(&ctx->iopoll_list) \|\| to_submit) {
	const struct cred *creds = NULL;

	if (ctx->sq_creds != current_cred())
	creds = override_creds(ctx->sq_creds);

	mutex_lock(&ctx->uring_lock);
	if (!wq_list_empty(&ctx->iopoll_list))
	io_do_iopoll(ctx, true);

	/*
	* Don't submit if refs are dying, good for io_uring_register(),
	* but also it is relied upon by io_ring_exit_work()
	*/
	if (to_submit && likely(!percpu_ref_is_dying(&ctx->refs)) &&
	!(ctx->flags & IORING_SETUP_R_DISABLED))
	ret = io_submit_sqes(ctx, to_submit);
	mutex_unlock(&ctx->uring_lock);

	if (to_submit && wq_has_sleeper(&ctx->sqo_sq_wait))
	wake_up(&ctx->sqo_sq_wait);
	if (creds)
	revert_creds(creds);
	}

	return ret;
	}

	static bool io_sqd_handle_event(struct io_sq_data *sqd)
	{
	bool did_sig = false;
	struct ksignal ksig;

	if (test_bit(IO_SQ_THREAD_SHOULD_PARK, &sqd->state) \|\|
	signal_pending(current)) {
	mutex_unlock(&sqd->lock);
	if (signal_pending(current))
	did_sig = get_signal(&ksig);
	cond_resched();
	mutex_lock(&sqd->lock);
	}
	return did_sig \|\| test_bit(IO_SQ_THREAD_SHOULD_STOP, &sqd->state);
	}

	static int io_sq_thread(void *data)
	{
	struct io_sq_data *sqd = data;
	struct io_ring_ctx *ctx;
	unsigned long timeout = 0;
	char buf[TASK_COMM_LEN];
	DEFINE_WAIT(wait);

	snprintf(buf, sizeof(buf), "iou-sqp-%d", sqd->task_pid);
	set_task_comm(current, buf);

	if (sqd->sq_cpu != -1)
	set_cpus_allowed_ptr(current, cpumask_of(sqd->sq_cpu));
	else
	set_cpus_allowed_ptr(current, cpu_online_mask);
	current->flags \|= PF_NO_SETAFFINITY;

	mutex_lock(&sqd->lock);
	while (1) {
	bool cap_entries, sqt_spin = false;

	if (io_sqd_events_pending(sqd) \|\| signal_pending(current)) {
	if (io_sqd_handle_event(sqd))
	break;
	timeout = jiffies + sqd->sq_thread_idle;
	}

	cap_entries = !list_is_singular(&sqd->ctx_list);
	list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
	int ret = __io_sq_thread(ctx, cap_entries);

	if (!sqt_spin && (ret > 0 \|\| !wq_list_empty(&ctx->iopoll_list)))
	sqt_spin = true;
	}
	if (io_run_task_work())
	sqt_spin = true;

	if (sqt_spin \|\| !time_after(jiffies, timeout)) {
	cond_resched();
	if (sqt_spin)
	timeout = jiffies + sqd->sq_thread_idle;
	continue;
	}

	prepare_to_wait(&sqd->wait, &wait, TASK_INTERRUPTIBLE);
	if (!io_sqd_events_pending(sqd) && !task_work_pending(current)) {
	bool needs_sched = true;

	list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
	atomic_or(IORING_SQ_NEED_WAKEUP,
	&ctx->rings->sq_flags);
	if ((ctx->flags & IORING_SETUP_IOPOLL) &&
	!wq_list_empty(&ctx->iopoll_list)) {
	needs_sched = false;
	break;
	}

	/*
	* Ensure the store of the wakeup flag is not
	* reordered with the load of the SQ tail
	*/
	smp_mb__after_atomic();

	if (io_sqring_entries(ctx)) {
	needs_sched = false;
	break;
	}
	}

	if (needs_sched) {
	mutex_unlock(&sqd->lock);
	schedule();
	mutex_lock(&sqd->lock);
	}
	list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
	atomic_andnot(IORING_SQ_NEED_WAKEUP,
	&ctx->rings->sq_flags);
	}

	finish_wait(&sqd->wait, &wait);
	timeout = jiffies + sqd->sq_thread_idle;
	}

	io_uring_cancel_generic(true, sqd);
	sqd->thread = NULL;
	list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
	atomic_or(IORING_SQ_NEED_WAKEUP, &ctx->rings->sq_flags);
	io_run_task_work();
	mutex_unlock(&sqd->lock);

	complete(&sqd->exited);
	do_exit(0);
	}

	int io_sqpoll_wait_sq(struct io_ring_ctx *ctx)
	{
	DEFINE_WAIT(wait);

	do {
	if (!io_sqring_full(ctx))
	break;
	prepare_to_wait(&ctx->sqo_sq_wait, &wait, TASK_INTERRUPTIBLE);

	if (!io_sqring_full(ctx))
	break;
	schedule();
	} while (!signal_pending(current));

	finish_wait(&ctx->sqo_sq_wait, &wait);
	return 0;
	}

	__cold int io_sq_offload_create(struct io_ring_ctx *ctx,
	struct io_uring_params *p)
	{
	int ret;

	/* Retain compatibility with failing for an invalid attach attempt */
	if ((ctx->flags & (IORING_SETUP_ATTACH_WQ \| IORING_SETUP_SQPOLL)) ==
	IORING_SETUP_ATTACH_WQ) {
	struct fd f;

	f = fdget(p->wq_fd);
	if (!f.file)
	return -ENXIO;
	if (!io_is_uring_fops(f.file)) {
	fdput(f);
	return -EINVAL;
	}
	fdput(f);
	}
	if (ctx->flags & IORING_SETUP_SQPOLL) {
	struct task_struct *tsk;
	struct io_sq_data *sqd;
	bool attached;

	ret = security_uring_sqpoll();
	if (ret)
	return ret;

	sqd = io_get_sq_data(p, &attached);
	if (IS_ERR(sqd)) {
	ret = PTR_ERR(sqd);
	goto err;
	}

	ctx->sq_creds = get_current_cred();
	ctx->sq_data = sqd;
	ctx->sq_thread_idle = msecs_to_jiffies(p->sq_thread_idle);
	if (!ctx->sq_thread_idle)
	ctx->sq_thread_idle = HZ;

	io_sq_thread_park(sqd);
	list_add(&ctx->sqd_list, &sqd->ctx_list);
	io_sqd_update_thread_idle(sqd);
	/* don't attach to a dying SQPOLL thread, would be racy */
	ret = (attached && !sqd->thread) ? -ENXIO : 0;
	io_sq_thread_unpark(sqd);

	if (ret < 0)
	goto err;
	if (attached)
	return 0;

	if (p->flags & IORING_SETUP_SQ_AFF) {
	int cpu = p->sq_thread_cpu;

	ret = -EINVAL;
	if (cpu >= nr_cpu_ids \|\| !cpu_online(cpu))
	goto err_sqpoll;
	sqd->sq_cpu = cpu;
	} else {
	sqd->sq_cpu = -1;
	}

	sqd->task_pid = current->pid;
	sqd->task_tgid = current->tgid;
	tsk = create_io_thread(io_sq_thread, sqd, NUMA_NO_NODE);
	if (IS_ERR(tsk)) {
	ret = PTR_ERR(tsk);
	goto err_sqpoll;
	}

	sqd->thread = tsk;
	ret = io_uring_alloc_task_context(tsk, ctx);
	wake_up_new_task(tsk);
	if (ret)
	goto err;
	} else if (p->flags & IORING_SETUP_SQ_AFF) {
	/* Can't have SQ_AFF without SQPOLL */
	ret = -EINVAL;
	goto err;
	}

	return 0;
	err_sqpoll:
	complete(&ctx->sq_data->exited);
	err:
	io_sq_thread_finish(ctx);
	return ret;
	}