blk-ioc.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Functions related to io context handling
  4 */
  5#include <linux/kernel.h>
  6#include <linux/module.h>
  7#include <linux/init.h>
  8#include <linux/bio.h>
  9#include <linux/blkdev.h>
 10#include <linux/slab.h>
 11#include <linux/security.h>
 12#include <linux/sched/task.h>
 13
 14#include "blk.h"
 15#include "blk-mq-sched.h"
 16
 17/*
 18 * For io context allocations
 19 */
 20static struct kmem_cache *iocontext_cachep;
 21
 22#ifdef CONFIG_BLK_ICQ
 23/**
 24 * get_io_context - increment reference count to io_context
 25 * @ioc: io_context to get
 26 *
 27 * Increment reference count to @ioc.
 28 */
 29static void get_io_context(struct io_context *ioc)
 30{
 31	BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
 32	atomic_long_inc(&ioc->refcount);
 33}
 34
 35/*
 36 * Exit an icq. Called with ioc locked for blk-mq, and with both ioc
 37 * and queue locked for legacy.
 38 */
 39static void ioc_exit_icq(struct io_cq *icq)
 40{
 41	struct elevator_type *et = icq->q->elevator->type;
 42
 43	if (icq->flags & ICQ_EXITED)
 44		return;
 45
 46	if (et->ops.exit_icq)
 47		et->ops.exit_icq(icq);
 48
 49	icq->flags |= ICQ_EXITED;
 50}
 51
 52static void ioc_exit_icqs(struct io_context *ioc)
 53{
 54	struct io_cq *icq;
 55
 56	spin_lock_irq(&ioc->lock);
 57	hlist_for_each_entry(icq, &ioc->icq_list, ioc_node)
 58		ioc_exit_icq(icq);
 59	spin_unlock_irq(&ioc->lock);
 60}
 61
 62/*
 63 * Release an icq. Called with ioc locked for blk-mq, and with both ioc
 64 * and queue locked for legacy.
 65 */
 66static void ioc_destroy_icq(struct io_cq *icq)
 67{
 68	struct io_context *ioc = icq->ioc;
 69	struct request_queue *q = icq->q;
 70	struct elevator_type *et = q->elevator->type;
 71
 72	lockdep_assert_held(&ioc->lock);
 73	lockdep_assert_held(&q->queue_lock);
 74
 75	if (icq->flags & ICQ_DESTROYED)
 76		return;
 77
 78	radix_tree_delete(&ioc->icq_tree, icq->q->id);
 79	hlist_del_init(&icq->ioc_node);
 80	list_del_init(&icq->q_node);
 81
 82	/*
 83	 * Both setting lookup hint to and clearing it from @icq are done
 84	 * under queue_lock.  If it's not pointing to @icq now, it never
 85	 * will.  Hint assignment itself can race safely.
 86	 */
 87	if (rcu_access_pointer(ioc->icq_hint) == icq)
 88		rcu_assign_pointer(ioc->icq_hint, NULL);
 89
 90	ioc_exit_icq(icq);
 91
 92	/*
 93	 * @icq->q might have gone away by the time RCU callback runs
 94	 * making it impossible to determine icq_cache.  Record it in @icq.
 95	 */
 96	icq->__rcu_icq_cache = et->icq_cache;
 97	icq->flags |= ICQ_DESTROYED;
 98	kfree_rcu(icq, __rcu_head);
 99}
100
101/*
102 * Slow path for ioc release in put_io_context().  Performs double-lock
103 * dancing to unlink all icq's and then frees ioc.
104 */
105static void ioc_release_fn(struct work_struct *work)
106{
107	struct io_context *ioc = container_of(work, struct io_context,
108					      release_work);
109	spin_lock_irq(&ioc->lock);
110
111	while (!hlist_empty(&ioc->icq_list)) {
112		struct io_cq *icq = hlist_entry(ioc->icq_list.first,
113						struct io_cq, ioc_node);
114		struct request_queue *q = icq->q;
115
116		if (spin_trylock(&q->queue_lock)) {
117			ioc_destroy_icq(icq);
118			spin_unlock(&q->queue_lock);
119		} else {
120			/* Make sure q and icq cannot be freed. */
121			rcu_read_lock();
122
123			/* Re-acquire the locks in the correct order. */
124			spin_unlock(&ioc->lock);
125			spin_lock(&q->queue_lock);
126			spin_lock(&ioc->lock);
127
128			ioc_destroy_icq(icq);
129
130			spin_unlock(&q->queue_lock);
131			rcu_read_unlock();
132		}
133	}
134
135	spin_unlock_irq(&ioc->lock);
136
137	kmem_cache_free(iocontext_cachep, ioc);
138}
139
140/*
141 * Releasing icqs requires reverse order double locking and we may already be
142 * holding a queue_lock.  Do it asynchronously from a workqueue.
143 */
144static bool ioc_delay_free(struct io_context *ioc)
145{
146	unsigned long flags;
147
148	spin_lock_irqsave(&ioc->lock, flags);
149	if (!hlist_empty(&ioc->icq_list)) {
150		queue_work(system_power_efficient_wq, &ioc->release_work);
151		spin_unlock_irqrestore(&ioc->lock, flags);
152		return true;
153	}
154	spin_unlock_irqrestore(&ioc->lock, flags);
155	return false;
156}
157
158/**
159 * ioc_clear_queue - break any ioc association with the specified queue
160 * @q: request_queue being cleared
161 *
162 * Walk @q->icq_list and exit all io_cq's.
163 */
164void ioc_clear_queue(struct request_queue *q)
165{
166	spin_lock_irq(&q->queue_lock);
167	while (!list_empty(&q->icq_list)) {
168		struct io_cq *icq =
169			list_first_entry(&q->icq_list, struct io_cq, q_node);
170
171		/*
172		 * Other context won't hold ioc lock to wait for queue_lock, see
173		 * details in ioc_release_fn().
174		 */
175		spin_lock(&icq->ioc->lock);
176		ioc_destroy_icq(icq);
177		spin_unlock(&icq->ioc->lock);
178	}
179	spin_unlock_irq(&q->queue_lock);
180}
181#else /* CONFIG_BLK_ICQ */
182static inline void ioc_exit_icqs(struct io_context *ioc)
183{
184}
185static inline bool ioc_delay_free(struct io_context *ioc)
186{
187	return false;
188}
189#endif /* CONFIG_BLK_ICQ */
190
191/**
192 * put_io_context - put a reference of io_context
193 * @ioc: io_context to put
194 *
195 * Decrement reference count of @ioc and release it if the count reaches
196 * zero.
197 */
198void put_io_context(struct io_context *ioc)
199{
200	BUG_ON(atomic_long_read(&ioc->refcount) <= 0);
201	if (atomic_long_dec_and_test(&ioc->refcount) && !ioc_delay_free(ioc))
202		kmem_cache_free(iocontext_cachep, ioc);
203}
204EXPORT_SYMBOL_GPL(put_io_context);
205
206/* Called by the exiting task */
207void exit_io_context(struct task_struct *task)
208{
209	struct io_context *ioc;
210
211	task_lock(task);
212	ioc = task->io_context;
213	task->io_context = NULL;
214	task_unlock(task);
215
216	if (atomic_dec_and_test(&ioc->active_ref)) {
217		ioc_exit_icqs(ioc);
218		put_io_context(ioc);
219	}
220}
221
222static struct io_context *alloc_io_context(gfp_t gfp_flags, int node)
223{
224	struct io_context *ioc;
225
226	ioc = kmem_cache_alloc_node(iocontext_cachep, gfp_flags | __GFP_ZERO,
227				    node);
228	if (unlikely(!ioc))
229		return NULL;
230
231	atomic_long_set(&ioc->refcount, 1);
232	atomic_set(&ioc->active_ref, 1);
233#ifdef CONFIG_BLK_ICQ
234	spin_lock_init(&ioc->lock);
235	INIT_RADIX_TREE(&ioc->icq_tree, GFP_ATOMIC);
236	INIT_HLIST_HEAD(&ioc->icq_list);
237	INIT_WORK(&ioc->release_work, ioc_release_fn);
238#endif
239	ioc->ioprio = IOPRIO_DEFAULT;
240
241	return ioc;
242}
243
244int set_task_ioprio(struct task_struct *task, int ioprio)
245{
246	int err;
247	const struct cred *cred = current_cred(), *tcred;
248
249	rcu_read_lock();
250	tcred = __task_cred(task);
251	if (!uid_eq(tcred->uid, cred->euid) &&
252	    !uid_eq(tcred->uid, cred->uid) && !capable(CAP_SYS_NICE)) {
253		rcu_read_unlock();
254		return -EPERM;
255	}
256	rcu_read_unlock();
257
258	err = security_task_setioprio(task, ioprio);
259	if (err)
260		return err;
261
262	task_lock(task);
263	if (unlikely(!task->io_context)) {
264		struct io_context *ioc;
265
266		task_unlock(task);
267
268		ioc = alloc_io_context(GFP_ATOMIC, NUMA_NO_NODE);
269		if (!ioc)
270			return -ENOMEM;
271
272		task_lock(task);
273		if (task->flags & PF_EXITING) {
274			kmem_cache_free(iocontext_cachep, ioc);
275			goto out;
276		}
277		if (task->io_context)
278			kmem_cache_free(iocontext_cachep, ioc);
279		else
280			task->io_context = ioc;
281	}
282	task->io_context->ioprio = ioprio;
283out:
284	task_unlock(task);
285	return 0;
286}
287EXPORT_SYMBOL_GPL(set_task_ioprio);
288
289int __copy_io(u64 clone_flags, struct task_struct *tsk)
290{
291	struct io_context *ioc = current->io_context;
292
293	/*
294	 * Share io context with parent, if CLONE_IO is set
295	 */
296	if (clone_flags & CLONE_IO) {
297		atomic_inc(&ioc->active_ref);
298		tsk->io_context = ioc;
299	} else if (ioprio_valid(ioc->ioprio)) {
300		tsk->io_context = alloc_io_context(GFP_KERNEL, NUMA_NO_NODE);
301		if (!tsk->io_context)
302			return -ENOMEM;
303		tsk->io_context->ioprio = ioc->ioprio;
304	}
305
306	return 0;
307}
308
309#ifdef CONFIG_BLK_ICQ
310/**
311 * ioc_lookup_icq - lookup io_cq from ioc in io issue path
312 * @q: the associated request_queue
313 *
314 * Look up io_cq associated with @ioc - @q pair from @ioc.  Must be called
315 * from io issue path, either return NULL if current issue io to @q for the
316 * first time, or return a valid icq.
317 */
318struct io_cq *ioc_lookup_icq(struct request_queue *q)
319{
320	struct io_context *ioc = current->io_context;
321	struct io_cq *icq;
322
323	/*
324	 * icq's are indexed from @ioc using radix tree and hint pointer,
325	 * both of which are protected with RCU, io issue path ensures that
326	 * both request_queue and current task are valid, the found icq
327	 * is guaranteed to be valid until the io is done.
328	 */
329	rcu_read_lock();
330	icq = rcu_dereference(ioc->icq_hint);
331	if (icq && icq->q == q)
332		goto out;
333
334	icq = radix_tree_lookup(&ioc->icq_tree, q->id);
335	if (icq && icq->q == q)
336		rcu_assign_pointer(ioc->icq_hint, icq);	/* allowed to race */
337	else
338		icq = NULL;
339out:
340	rcu_read_unlock();
341	return icq;
342}
343EXPORT_SYMBOL(ioc_lookup_icq);
344
345/**
346 * ioc_create_icq - create and link io_cq
347 * @q: request_queue of interest
348 *
349 * Make sure io_cq linking @ioc and @q exists.  If icq doesn't exist, they
350 * will be created using @gfp_mask.
351 *
352 * The caller is responsible for ensuring @ioc won't go away and @q is
353 * alive and will stay alive until this function returns.
354 */
355static struct io_cq *ioc_create_icq(struct request_queue *q)
356{
357	struct io_context *ioc = current->io_context;
358	struct elevator_type *et = q->elevator->type;
359	struct io_cq *icq;
360
361	/* allocate stuff */
362	icq = kmem_cache_alloc_node(et->icq_cache, GFP_ATOMIC | __GFP_ZERO,
363				    q->node);
364	if (!icq)
365		return NULL;
366
367	if (radix_tree_maybe_preload(GFP_ATOMIC) < 0) {
368		kmem_cache_free(et->icq_cache, icq);
369		return NULL;
370	}
371
372	icq->ioc = ioc;
373	icq->q = q;
374	INIT_LIST_HEAD(&icq->q_node);
375	INIT_HLIST_NODE(&icq->ioc_node);
376
377	/* lock both q and ioc and try to link @icq */
378	spin_lock_irq(&q->queue_lock);
379	spin_lock(&ioc->lock);
380
381	if (likely(!radix_tree_insert(&ioc->icq_tree, q->id, icq))) {
382		hlist_add_head(&icq->ioc_node, &ioc->icq_list);
383		list_add(&icq->q_node, &q->icq_list);
384		if (et->ops.init_icq)
385			et->ops.init_icq(icq);
386	} else {
387		kmem_cache_free(et->icq_cache, icq);
388		icq = ioc_lookup_icq(q);
389		if (!icq)
390			printk(KERN_ERR "cfq: icq link failed!\n");
391	}
392
393	spin_unlock(&ioc->lock);
394	spin_unlock_irq(&q->queue_lock);
395	radix_tree_preload_end();
396	return icq;
397}
398
399struct io_cq *ioc_find_get_icq(struct request_queue *q)
400{
401	struct io_context *ioc = current->io_context;
402	struct io_cq *icq = NULL;
403
404	if (unlikely(!ioc)) {
405		ioc = alloc_io_context(GFP_ATOMIC, q->node);
406		if (!ioc)
407			return NULL;
408
409		task_lock(current);
410		if (current->io_context) {
411			kmem_cache_free(iocontext_cachep, ioc);
412			ioc = current->io_context;
413		} else {
414			current->io_context = ioc;
415		}
416
417		get_io_context(ioc);
418		task_unlock(current);
419	} else {
420		get_io_context(ioc);
421		icq = ioc_lookup_icq(q);
422	}
423
424	if (!icq) {
425		icq = ioc_create_icq(q);
426		if (!icq) {
427			put_io_context(ioc);
428			return NULL;
429		}
430	}
431	return icq;
432}
433EXPORT_SYMBOL_GPL(ioc_find_get_icq);
434#endif /* CONFIG_BLK_ICQ */
435
436static int __init blk_ioc_init(void)
437{
438	iocontext_cachep = kmem_cache_create("blkdev_ioc",
439			sizeof(struct io_context), 0, SLAB_PANIC, NULL);
440	return 0;
441}
442subsys_initcall(blk_ioc_init);