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-rw-r--r--fs/erofs/utils.c292
1 files changed, 292 insertions, 0 deletions
diff --git a/fs/erofs/utils.c b/fs/erofs/utils.c
new file mode 100644
index 000000000..46627cb69
--- /dev/null
+++ b/fs/erofs/utils.c
@@ -0,0 +1,292 @@
+// 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 */