fs/erofs/utils.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (C) 2018 HUAWEI, Inc.
  *             https://www.huawei.com/
  */
 #include "internal.h"
 #include <linux/pagevec.h>

 struct page *erofs_allocpage(struct page **pagepool, gfp_t gfp)
 {
 	struct page *page = *pagepool;

 	if (page) {
 		DBG_BUGON(page_ref_count(page) != 1);
 		*pagepool = (struct page *)page_private(page);
 	} else {
 		page = alloc_page(gfp);
 	}
 	return page;
 }

 void erofs_release_pages(struct page **pagepool)
 {
 	while (*pagepool) {
 		struct page *page = *pagepool;

 		*pagepool = (struct page *)page_private(page);
 		put_page(page);
 	}
 }

 #ifdef CONFIG_EROFS_FS_ZIP
 /* global shrink count (for all mounted EROFS instances) */
 static atomic_long_t erofs_global_shrink_cnt;

 static int erofs_workgroup_get(struct erofs_workgroup *grp)
 {
 	int o;

 repeat:
 	o = erofs_wait_on_workgroup_freezed(grp);
 	if (o <= 0)
 		return -1;

 	if (atomic_cmpxchg(&grp->refcount, o, o + 1) != o)
 		goto repeat;

 	/* decrease refcount paired by erofs_workgroup_put */
 	if (o == 1)
 		atomic_long_dec(&erofs_global_shrink_cnt);
 	return 0;
 }

 struct erofs_workgroup *erofs_find_workgroup(struct super_block *sb,
 					     pgoff_t index)
 {
 	struct erofs_sb_info *sbi = EROFS_SB(sb);
 	struct erofs_workgroup *grp;

 repeat:
 	rcu_read_lock();
 	grp = xa_load(&sbi->managed_pslots, index);
 	if (grp) {
 		if (erofs_workgroup_get(grp)) {
 			/* prefer to relax rcu read side */
 			rcu_read_unlock();
 			goto repeat;
 		}

 		DBG_BUGON(index != grp->index);
 	}
 	rcu_read_unlock();
 	return grp;
 }

 struct erofs_workgroup *erofs_insert_workgroup(struct super_block *sb,
 					       struct erofs_workgroup *grp)
 {
 	struct erofs_sb_info *const sbi = EROFS_SB(sb);
 	struct erofs_workgroup *pre;

 	/*
 	 * Bump up a reference count before making this visible
 	 * to others for the XArray in order to avoid potential
 	 * UAF without serialized by xa_lock.
 	 */
 	atomic_inc(&grp->refcount);

 repeat:
 	xa_lock(&sbi->managed_pslots);
 	pre = __xa_cmpxchg(&sbi->managed_pslots, grp->index,
 			   NULL, grp, GFP_NOFS);
 	if (pre) {
 		if (xa_is_err(pre)) {
 			pre = ERR_PTR(xa_err(pre));
 		} else if (erofs_workgroup_get(pre)) {
 			/* try to legitimize the current in-tree one */
 			xa_unlock(&sbi->managed_pslots);
 			cond_resched();
 			goto repeat;
 		}
 		atomic_dec(&grp->refcount);
 		grp = pre;
 	}
 	xa_unlock(&sbi->managed_pslots);
 	return grp;
 }

 static void  __erofs_workgroup_free(struct erofs_workgroup *grp)
 {
 	atomic_long_dec(&erofs_global_shrink_cnt);
 	erofs_workgroup_free_rcu(grp);
 }

 int erofs_workgroup_put(struct erofs_workgroup *grp)
 {
 	int count = atomic_dec_return(&grp->refcount);

 	if (count == 1)
 		atomic_long_inc(&erofs_global_shrink_cnt);
 	else if (!count)
 		__erofs_workgroup_free(grp);
 	return count;
 }

 static bool erofs_try_to_release_workgroup(struct erofs_sb_info *sbi,
 					   struct erofs_workgroup *grp)
 {
 	/*
 	 * If managed cache is on, refcount of workgroups
 	 * themselves could be < 0 (freezed). In other words,
 	 * there is no guarantee that all refcounts > 0.
 	 */
 	if (!erofs_workgroup_try_to_freeze(grp, 1))
 		return false;

 	/*
 	 * Note that all cached pages should be unattached
 	 * before deleted from the XArray. Otherwise some
 	 * cached pages could be still attached to the orphan
 	 * old workgroup when the new one is available in the tree.
 	 */
 	if (erofs_try_to_free_all_cached_pages(sbi, grp)) {
 		erofs_workgroup_unfreeze(grp, 1);
 		return false;
 	}

 	/*
 	 * It's impossible to fail after the workgroup is freezed,
 	 * however in order to avoid some race conditions, add a
 	 * DBG_BUGON to observe this in advance.
 	 */
 	DBG_BUGON(__xa_erase(&sbi->managed_pslots, grp->index) != grp);

 	/* last refcount should be connected with its managed pslot.  */
 	erofs_workgroup_unfreeze(grp, 0);
 	__erofs_workgroup_free(grp);
 	return true;
 }

 static unsigned long erofs_shrink_workstation(struct erofs_sb_info *sbi,
 					      unsigned long nr_shrink)
 {
 	struct erofs_workgroup *grp;
 	unsigned int freed = 0;
 	unsigned long index;

 	xa_lock(&sbi->managed_pslots);
 	xa_for_each(&sbi->managed_pslots, index, grp) {
 		/* try to shrink each valid workgroup */
 		if (!erofs_try_to_release_workgroup(sbi, grp))
 			continue;
 		xa_unlock(&sbi->managed_pslots);

 		++freed;
 		if (!--nr_shrink)
 			return freed;
 		xa_lock(&sbi->managed_pslots);
 	}
 	xa_unlock(&sbi->managed_pslots);
 	return freed;
 }

 /* protected by 'erofs_sb_list_lock' */
 static unsigned int shrinker_run_no;

 /* protects the mounted 'erofs_sb_list' */
 static DEFINE_SPINLOCK(erofs_sb_list_lock);
 static LIST_HEAD(erofs_sb_list);

 void erofs_shrinker_register(struct super_block *sb)
 {
 	struct erofs_sb_info *sbi = EROFS_SB(sb);

 	mutex_init(&sbi->umount_mutex);

 	spin_lock(&erofs_sb_list_lock);
 	list_add(&sbi->list, &erofs_sb_list);
 	spin_unlock(&erofs_sb_list_lock);
 }

 void erofs_shrinker_unregister(struct super_block *sb)
 {
 	struct erofs_sb_info *const sbi = EROFS_SB(sb);

 	mutex_lock(&sbi->umount_mutex);
 	/* clean up all remaining workgroups in memory */
 	erofs_shrink_workstation(sbi, ~0UL);

 	spin_lock(&erofs_sb_list_lock);
 	list_del(&sbi->list);
 	spin_unlock(&erofs_sb_list_lock);
 	mutex_unlock(&sbi->umount_mutex);
 }

 static unsigned long erofs_shrink_count(struct shrinker *shrink,
 					struct shrink_control *sc)
 {
 	return atomic_long_read(&erofs_global_shrink_cnt);
 }

 static unsigned long erofs_shrink_scan(struct shrinker *shrink,
 				       struct shrink_control *sc)
 {
 	struct erofs_sb_info *sbi;
 	struct list_head *p;

 	unsigned long nr = sc->nr_to_scan;
 	unsigned int run_no;
 	unsigned long freed = 0;

 	spin_lock(&erofs_sb_list_lock);
 	do {
 		run_no = ++shrinker_run_no;
 	} while (run_no == 0);

 	/* Iterate over all mounted superblocks and try to shrink them */
 	p = erofs_sb_list.next;
 	while (p != &erofs_sb_list) {
 		sbi = list_entry(p, struct erofs_sb_info, list);

 		/*
 		 * We move the ones we do to the end of the list, so we stop
 		 * when we see one we have already done.
 		 */
 		if (sbi->shrinker_run_no == run_no)
 			break;

 		if (!mutex_trylock(&sbi->umount_mutex)) {
 			p = p->next;
 			continue;
 		}

 		spin_unlock(&erofs_sb_list_lock);
 		sbi->shrinker_run_no = run_no;

 		freed += erofs_shrink_workstation(sbi, nr - freed);

 		spin_lock(&erofs_sb_list_lock);
 		/* Get the next list element before we move this one */
 		p = p->next;

 		/*
 		 * Move this one to the end of the list to provide some
 		 * fairness.
 		 */
 		list_move_tail(&sbi->list, &erofs_sb_list);
 		mutex_unlock(&sbi->umount_mutex);

 		if (freed >= nr)
 			break;
 	}
 	spin_unlock(&erofs_sb_list_lock);
 	return freed;
 }

 static struct shrinker erofs_shrinker_info = {
 	.scan_objects = erofs_shrink_scan,
 	.count_objects = erofs_shrink_count,
 	.seeks = DEFAULT_SEEKS,
 };

 int __init erofs_init_shrinker(void)
 {
 	return register_shrinker(&erofs_shrinker_info, "erofs-shrinker");
 }

 void erofs_exit_shrinker(void)
 {
 	unregister_shrinker(&erofs_shrinker_info);
 }
 #endif	/* !CONFIG_EROFS_FS_ZIP */
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* Copyright (C) 2018 HUAWEI, Inc.
	* https://www.huawei.com/
	*/
	#include "internal.h"
	#include <linux/pagevec.h>

	struct page erofs_allocpage(struct page *pagepool, gfp_t gfp)
	{
	struct page page = pagepool;

	if (page) {
	DBG_BUGON(page_ref_count(page) != 1);
	pagepool = (struct page )page_private(page);
	} else {
	page = alloc_page(gfp);
	}
	return page;
	}

	void erofs_release_pages(struct page **pagepool)
	{
	while (*pagepool) {
	struct page page = pagepool;

	pagepool = (struct page )page_private(page);
	put_page(page);
	}
	}

	#ifdef CONFIG_EROFS_FS_ZIP
	/* global shrink count (for all mounted EROFS instances) */
	static atomic_long_t erofs_global_shrink_cnt;

	static int erofs_workgroup_get(struct erofs_workgroup *grp)
	{
	int o;

	repeat:
	o = erofs_wait_on_workgroup_freezed(grp);
	if (o <= 0)
	return -1;

	if (atomic_cmpxchg(&grp->refcount, o, o + 1) != o)
	goto repeat;

	/* decrease refcount paired by erofs_workgroup_put */
	if (o == 1)
	atomic_long_dec(&erofs_global_shrink_cnt);
	return 0;
	}

	struct erofs_workgroup erofs_find_workgroup(struct super_block sb,
	pgoff_t index)
	{
	struct erofs_sb_info *sbi = EROFS_SB(sb);
	struct erofs_workgroup *grp;

	repeat:
	rcu_read_lock();
	grp = xa_load(&sbi->managed_pslots, index);
	if (grp) {
	if (erofs_workgroup_get(grp)) {
	/* prefer to relax rcu read side */
	rcu_read_unlock();
	goto repeat;
	}

	DBG_BUGON(index != grp->index);
	}
	rcu_read_unlock();
	return grp;
	}

	struct erofs_workgroup erofs_insert_workgroup(struct super_block sb,
	struct erofs_workgroup *grp)
	{
	struct erofs_sb_info *const sbi = EROFS_SB(sb);
	struct erofs_workgroup *pre;

	/*
	* Bump up a reference count before making this visible
	* to others for the XArray in order to avoid potential
	* UAF without serialized by xa_lock.
	*/
	atomic_inc(&grp->refcount);

	repeat:
	xa_lock(&sbi->managed_pslots);
	pre = __xa_cmpxchg(&sbi->managed_pslots, grp->index,
	NULL, grp, GFP_NOFS);
	if (pre) {
	if (xa_is_err(pre)) {
	pre = ERR_PTR(xa_err(pre));
	} else if (erofs_workgroup_get(pre)) {
	/* try to legitimize the current in-tree one */
	xa_unlock(&sbi->managed_pslots);
	cond_resched();
	goto repeat;
	}
	atomic_dec(&grp->refcount);
	grp = pre;
	}
	xa_unlock(&sbi->managed_pslots);
	return grp;
	}

	static void __erofs_workgroup_free(struct erofs_workgroup *grp)
	{
	atomic_long_dec(&erofs_global_shrink_cnt);
	erofs_workgroup_free_rcu(grp);
	}

	int erofs_workgroup_put(struct erofs_workgroup *grp)
	{
	int count = atomic_dec_return(&grp->refcount);

	if (count == 1)
	atomic_long_inc(&erofs_global_shrink_cnt);
	else if (!count)
	__erofs_workgroup_free(grp);
	return count;
	}

	static bool erofs_try_to_release_workgroup(struct erofs_sb_info *sbi,
	struct erofs_workgroup *grp)
	{
	/*
	* If managed cache is on, refcount of workgroups
	* themselves could be < 0 (freezed). In other words,
	* there is no guarantee that all refcounts > 0.
	*/
	if (!erofs_workgroup_try_to_freeze(grp, 1))
	return false;

	/*
	* Note that all cached pages should be unattached
	* before deleted from the XArray. Otherwise some
	* cached pages could be still attached to the orphan
	* old workgroup when the new one is available in the tree.
	*/
	if (erofs_try_to_free_all_cached_pages(sbi, grp)) {
	erofs_workgroup_unfreeze(grp, 1);
	return false;
	}

	/*
	* It's impossible to fail after the workgroup is freezed,
	* however in order to avoid some race conditions, add a
	* DBG_BUGON to observe this in advance.
	*/
	DBG_BUGON(__xa_erase(&sbi->managed_pslots, grp->index) != grp);

	/* last refcount should be connected with its managed pslot. */
	erofs_workgroup_unfreeze(grp, 0);
	__erofs_workgroup_free(grp);
	return true;
	}

	static unsigned long erofs_shrink_workstation(struct erofs_sb_info *sbi,
	unsigned long nr_shrink)
	{
	struct erofs_workgroup *grp;
	unsigned int freed = 0;
	unsigned long index;

	xa_lock(&sbi->managed_pslots);
	xa_for_each(&sbi->managed_pslots, index, grp) {
	/* try to shrink each valid workgroup */
	if (!erofs_try_to_release_workgroup(sbi, grp))
	continue;
	xa_unlock(&sbi->managed_pslots);

	++freed;
	if (!--nr_shrink)
	return freed;
	xa_lock(&sbi->managed_pslots);
	}
	xa_unlock(&sbi->managed_pslots);
	return freed;
	}

	/* protected by 'erofs_sb_list_lock' */
	static unsigned int shrinker_run_no;

	/* protects the mounted 'erofs_sb_list' */
	static DEFINE_SPINLOCK(erofs_sb_list_lock);
	static LIST_HEAD(erofs_sb_list);

	void erofs_shrinker_register(struct super_block *sb)
	{
	struct erofs_sb_info *sbi = EROFS_SB(sb);

	mutex_init(&sbi->umount_mutex);

	spin_lock(&erofs_sb_list_lock);
	list_add(&sbi->list, &erofs_sb_list);
	spin_unlock(&erofs_sb_list_lock);
	}

	void erofs_shrinker_unregister(struct super_block *sb)
	{
	struct erofs_sb_info *const sbi = EROFS_SB(sb);

	mutex_lock(&sbi->umount_mutex);
	/* clean up all remaining workgroups in memory */
	erofs_shrink_workstation(sbi, ~0UL);

	spin_lock(&erofs_sb_list_lock);
	list_del(&sbi->list);
	spin_unlock(&erofs_sb_list_lock);
	mutex_unlock(&sbi->umount_mutex);
	}

	static unsigned long erofs_shrink_count(struct shrinker *shrink,
	struct shrink_control *sc)
	{
	return atomic_long_read(&erofs_global_shrink_cnt);
	}

	static unsigned long erofs_shrink_scan(struct shrinker *shrink,
	struct shrink_control *sc)
	{
	struct erofs_sb_info *sbi;
	struct list_head *p;

	unsigned long nr = sc->nr_to_scan;
	unsigned int run_no;
	unsigned long freed = 0;

	spin_lock(&erofs_sb_list_lock);
	do {
	run_no = ++shrinker_run_no;
	} while (run_no == 0);

	/* Iterate over all mounted superblocks and try to shrink them */
	p = erofs_sb_list.next;
	while (p != &erofs_sb_list) {
	sbi = list_entry(p, struct erofs_sb_info, list);

	/*
	* We move the ones we do to the end of the list, so we stop
	* when we see one we have already done.
	*/
	if (sbi->shrinker_run_no == run_no)
	break;

	if (!mutex_trylock(&sbi->umount_mutex)) {
	p = p->next;
	continue;
	}

	spin_unlock(&erofs_sb_list_lock);
	sbi->shrinker_run_no = run_no;

	freed += erofs_shrink_workstation(sbi, nr - freed);

	spin_lock(&erofs_sb_list_lock);
	/* Get the next list element before we move this one */
	p = p->next;

	/*
	* Move this one to the end of the list to provide some
	* fairness.
	*/
	list_move_tail(&sbi->list, &erofs_sb_list);
	mutex_unlock(&sbi->umount_mutex);

	if (freed >= nr)
	break;
	}
	spin_unlock(&erofs_sb_list_lock);
	return freed;
	}

	static struct shrinker erofs_shrinker_info = {
	.scan_objects = erofs_shrink_scan,
	.count_objects = erofs_shrink_count,
	.seeks = DEFAULT_SEEKS,
	};

	int __init erofs_init_shrinker(void)
	{
	return register_shrinker(&erofs_shrinker_info, "erofs-shrinker");
	}

	void erofs_exit_shrinker(void)
	{
	unregister_shrinker(&erofs_shrinker_info);
	}
	#endif /* !CONFIG_EROFS_FS_ZIP */