This is a second part to remove the mixed use of rb_tree in discard_cmd from
extent_cache.
This should also fix arm32 memory alignment issue caused by shared rb_entry.
[struct discard_cmd] [struct rb_entry]
[0] struct rb_node rb_node; [0] struct rb_node rb_node;
union { union {
struct { struct {
[16] block_t lstart; [12] unsigned int ofs;
block_t len; unsigned int len;
};
unsigned long long key;
} __packed;
Cc: <[email protected]>
Fixes: 004b68621897 ("f2fs: use rb-tree to track pending discard commands")
Signed-off-by: Jaegeuk Kim <[email protected]>
---
fs/f2fs/extent_cache.c | 36 +-----
fs/f2fs/f2fs.h | 23 +---
fs/f2fs/segment.c | 255 +++++++++++++++++++++++++++--------------
3 files changed, 172 insertions(+), 142 deletions(-)
diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c
index d1aa4609ca6b..5c206f941aac 100644
--- a/fs/f2fs/extent_cache.c
+++ b/fs/f2fs/extent_cache.c
@@ -192,7 +192,7 @@ static struct rb_entry *__lookup_rb_tree_slow(struct rb_root_cached *root,
return NULL;
}
-struct rb_entry *f2fs_lookup_rb_tree(struct rb_root_cached *root,
+static struct rb_entry *f2fs_lookup_rb_tree(struct rb_root_cached *root,
struct rb_entry *cached_re, unsigned int ofs)
{
struct rb_entry *re;
@@ -204,7 +204,7 @@ struct rb_entry *f2fs_lookup_rb_tree(struct rb_root_cached *root,
return re;
}
-struct rb_node **f2fs_lookup_rb_tree_for_insert(struct f2fs_sb_info *sbi,
+static struct rb_node **f2fs_lookup_rb_tree_for_insert(struct f2fs_sb_info *sbi,
struct rb_root_cached *root,
struct rb_node **parent,
unsigned int ofs, bool *leftmost)
@@ -238,7 +238,7 @@ struct rb_node **f2fs_lookup_rb_tree_for_insert(struct f2fs_sb_info *sbi,
* in order to simplify the insertion after.
* tree must stay unchanged between lookup and insertion.
*/
-struct rb_entry *f2fs_lookup_rb_tree_ret(struct rb_root_cached *root,
+static struct rb_entry *f2fs_lookup_rb_tree_ret(struct rb_root_cached *root,
struct rb_entry *cached_re,
unsigned int ofs,
struct rb_entry **prev_entry,
@@ -311,36 +311,6 @@ struct rb_entry *f2fs_lookup_rb_tree_ret(struct rb_root_cached *root,
return re;
}
-bool f2fs_check_rb_tree_consistence(struct f2fs_sb_info *sbi,
- struct rb_root_cached *root)
-{
-#ifdef CONFIG_F2FS_CHECK_FS
- struct rb_node *cur = rb_first_cached(root), *next;
- struct rb_entry *cur_re, *next_re;
-
- if (!cur)
- return true;
-
- while (cur) {
- next = rb_next(cur);
- if (!next)
- return true;
-
- cur_re = rb_entry(cur, struct rb_entry, rb_node);
- next_re = rb_entry(next, struct rb_entry, rb_node);
-
- if (cur_re->ofs + cur_re->len > next_re->ofs) {
- f2fs_info(sbi, "inconsistent rbtree, cur(%u, %u) next(%u, %u)",
- cur_re->ofs, cur_re->len,
- next_re->ofs, next_re->len);
- return false;
- }
- cur = next;
- }
-#endif
- return true;
-}
-
static struct kmem_cache *extent_tree_slab;
static struct kmem_cache *extent_node_slab;
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 9396549e112d..6e04fea9c34f 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -353,15 +353,7 @@ struct discard_info {
struct discard_cmd {
struct rb_node rb_node; /* rb node located in rb-tree */
- union {
- struct {
- block_t lstart; /* logical start address */
- block_t len; /* length */
- block_t start; /* actual start address in dev */
- };
- struct discard_info di; /* discard info */
-
- };
+ struct discard_info di; /* discard info */
struct list_head list; /* command list */
struct completion wait; /* compleation */
struct block_device *bdev; /* bdev */
@@ -4132,19 +4124,6 @@ void f2fs_leave_shrinker(struct f2fs_sb_info *sbi);
* extent_cache.c
*/
bool sanity_check_extent_cache(struct inode *inode);
-struct rb_entry *f2fs_lookup_rb_tree(struct rb_root_cached *root,
- struct rb_entry *cached_re, unsigned int ofs);
-struct rb_node **f2fs_lookup_rb_tree_for_insert(struct f2fs_sb_info *sbi,
- struct rb_root_cached *root,
- struct rb_node **parent,
- unsigned int ofs, bool *leftmost);
-struct rb_entry *f2fs_lookup_rb_tree_ret(struct rb_root_cached *root,
- struct rb_entry *cached_re, unsigned int ofs,
- struct rb_entry **prev_entry, struct rb_entry **next_entry,
- struct rb_node ***insert_p, struct rb_node **insert_parent,
- bool force, bool *leftmost);
-bool f2fs_check_rb_tree_consistence(struct f2fs_sb_info *sbi,
- struct rb_root_cached *root);
void f2fs_init_extent_tree(struct inode *inode);
void f2fs_drop_extent_tree(struct inode *inode);
void f2fs_destroy_extent_node(struct inode *inode);
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index e98a12e8dca1..961f5b149ee4 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -933,9 +933,9 @@ static struct discard_cmd *__create_discard_cmd(struct f2fs_sb_info *sbi,
dc = f2fs_kmem_cache_alloc(discard_cmd_slab, GFP_NOFS, true, NULL);
INIT_LIST_HEAD(&dc->list);
dc->bdev = bdev;
- dc->lstart = lstart;
- dc->start = start;
- dc->len = len;
+ dc->di.lstart = lstart;
+ dc->di.start = start;
+ dc->di.len = len;
dc->ref = 0;
dc->state = D_PREP;
dc->queued = 0;
@@ -950,20 +950,111 @@ static struct discard_cmd *__create_discard_cmd(struct f2fs_sb_info *sbi,
return dc;
}
-static struct discard_cmd *__attach_discard_cmd(struct f2fs_sb_info *sbi,
- struct block_device *bdev, block_t lstart,
- block_t start, block_t len,
- struct rb_node *parent, struct rb_node **p,
- bool leftmost)
+static bool f2fs_check_discard_tree(struct f2fs_sb_info *sbi)
+{
+#ifdef CONFIG_F2FS_CHECK_FS
+ struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
+ struct rb_node *cur = rb_first_cached(&dcc->root), *next;
+ struct discard_cmd *cur_dc, *next_dc;
+
+ if (!cur)
+ return true;
+
+ while (cur) {
+ next = rb_next(cur);
+ if (!next)
+ return true;
+
+ cur_dc = rb_entry(cur, struct discard_cmd, rb_node);
+ next_dc = rb_entry(next, struct discard_cmd, rb_node);
+
+ if (cur_dc->di.lstart + cur_dc->di.len > next_dc->di.lstart) {
+ f2fs_info(sbi, "broken discard_rbtree, "
+ "cur(%u, %u) next(%u, %u)",
+ cur_dc->di.lstart, cur_dc->di.len,
+ next_dc->di.lstart, next_dc->di.len);
+ return false;
+ }
+ cur = next;
+ }
+#endif
+ return true;
+}
+
+static struct discard_cmd *__lookup_discard_cmd(struct f2fs_sb_info *sbi,
+ block_t blkaddr)
{
struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
+ struct rb_node *node = dcc->root.rb_root.rb_node;
struct discard_cmd *dc;
- dc = __create_discard_cmd(sbi, bdev, lstart, start, len);
+ while (node) {
+ dc = rb_entry(node, struct discard_cmd, rb_node);
- rb_link_node(&dc->rb_node, parent, p);
- rb_insert_color_cached(&dc->rb_node, &dcc->root, leftmost);
+ if (blkaddr < dc->di.lstart)
+ node = node->rb_left;
+ else if (blkaddr >= dc->di.lstart + dc->di.len)
+ node = node->rb_right;
+ else
+ return dc;
+ }
+ return NULL;
+}
+
+static struct discard_cmd *__lookup_discard_cmd_ret(struct rb_root_cached *root,
+ block_t blkaddr,
+ struct discard_cmd **prev_entry,
+ struct discard_cmd **next_entry,
+ struct rb_node ***insert_p,
+ struct rb_node **insert_parent)
+{
+ struct rb_node **pnode = &root->rb_root.rb_node;
+ struct rb_node *parent = NULL, *tmp_node;
+ struct discard_cmd *dc;
+
+ *insert_p = NULL;
+ *insert_parent = NULL;
+ *prev_entry = NULL;
+ *next_entry = NULL;
+
+ if (RB_EMPTY_ROOT(&root->rb_root))
+ return NULL;
+
+ while (*pnode) {
+ parent = *pnode;
+ dc = rb_entry(*pnode, struct discard_cmd, rb_node);
+
+ if (blkaddr < dc->di.lstart)
+ pnode = &(*pnode)->rb_left;
+ else if (blkaddr >= dc->di.lstart + dc->di.len)
+ pnode = &(*pnode)->rb_right;
+ else
+ goto lookup_neighbors;
+ }
+ *insert_p = pnode;
+ *insert_parent = parent;
+
+ dc = rb_entry(parent, struct discard_cmd, rb_node);
+ tmp_node = parent;
+ if (parent && blkaddr > dc->di.lstart)
+ tmp_node = rb_next(parent);
+ *next_entry = rb_entry_safe(tmp_node, struct discard_cmd, rb_node);
+
+ tmp_node = parent;
+ if (parent && blkaddr < dc->di.lstart)
+ tmp_node = rb_prev(parent);
+ *prev_entry = rb_entry_safe(tmp_node, struct discard_cmd, rb_node);
+ return NULL;
+
+lookup_neighbors:
+ /* lookup prev node for merging backward later */
+ tmp_node = rb_prev(&dc->rb_node);
+ *prev_entry = rb_entry_safe(tmp_node, struct discard_cmd, rb_node);
+
+ /* lookup next node for merging frontward later */
+ tmp_node = rb_next(&dc->rb_node);
+ *next_entry = rb_entry_safe(tmp_node, struct discard_cmd, rb_node);
return dc;
}
@@ -975,7 +1066,7 @@ static void __detach_discard_cmd(struct discard_cmd_control *dcc,
list_del(&dc->list);
rb_erase_cached(&dc->rb_node, &dcc->root);
- dcc->undiscard_blks -= dc->len;
+ dcc->undiscard_blks -= dc->di.len;
kmem_cache_free(discard_cmd_slab, dc);
@@ -988,7 +1079,7 @@ static void __remove_discard_cmd(struct f2fs_sb_info *sbi,
struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
unsigned long flags;
- trace_f2fs_remove_discard(dc->bdev, dc->start, dc->len);
+ trace_f2fs_remove_discard(dc->bdev, dc->di.start, dc->di.len);
spin_lock_irqsave(&dc->lock, flags);
if (dc->bio_ref) {
@@ -1006,7 +1097,7 @@ static void __remove_discard_cmd(struct f2fs_sb_info *sbi,
printk_ratelimited(
"%sF2FS-fs (%s): Issue discard(%u, %u, %u) failed, ret: %d",
KERN_INFO, sbi->sb->s_id,
- dc->lstart, dc->start, dc->len, dc->error);
+ dc->di.lstart, dc->di.start, dc->di.len, dc->error);
__detach_discard_cmd(dcc, dc);
}
@@ -1122,14 +1213,14 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
if (is_sbi_flag_set(sbi, SBI_NEED_FSCK))
return 0;
- trace_f2fs_issue_discard(bdev, dc->start, dc->len);
+ trace_f2fs_issue_discard(bdev, dc->di.start, dc->di.len);
- lstart = dc->lstart;
- start = dc->start;
- len = dc->len;
+ lstart = dc->di.lstart;
+ start = dc->di.start;
+ len = dc->di.len;
total_len = len;
- dc->len = 0;
+ dc->di.len = 0;
while (total_len && *issued < dpolicy->max_requests && !err) {
struct bio *bio = NULL;
@@ -1145,7 +1236,7 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
if (*issued == dpolicy->max_requests)
last = true;
- dc->len += len;
+ dc->di.len += len;
if (time_to_inject(sbi, FAULT_DISCARD)) {
err = -EIO;
@@ -1207,34 +1298,41 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
return err;
}
-static void __insert_discard_tree(struct f2fs_sb_info *sbi,
+static void __insert_discard_cmd(struct f2fs_sb_info *sbi,
struct block_device *bdev, block_t lstart,
- block_t start, block_t len,
- struct rb_node **insert_p,
- struct rb_node *insert_parent)
+ block_t start, block_t len)
{
struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
- struct rb_node **p;
+ struct rb_node **p = &dcc->root.rb_root.rb_node;
struct rb_node *parent = NULL;
+ struct discard_cmd *dc;
bool leftmost = true;
- if (insert_p && insert_parent) {
- parent = insert_parent;
- p = insert_p;
- goto do_insert;
+ /* look up rb tree to find parent node */
+ while (*p) {
+ parent = *p;
+ dc = rb_entry(parent, struct discard_cmd, rb_node);
+
+ if (lstart < dc->di.lstart) {
+ p = &(*p)->rb_left;
+ } else if (lstart >= dc->di.lstart + dc->di.len) {
+ p = &(*p)->rb_right;
+ leftmost = false;
+ } else {
+ f2fs_bug_on(sbi, 1);
+ }
}
- p = f2fs_lookup_rb_tree_for_insert(sbi, &dcc->root, &parent,
- lstart, &leftmost);
-do_insert:
- __attach_discard_cmd(sbi, bdev, lstart, start, len, parent,
- p, leftmost);
+ dc = __create_discard_cmd(sbi, bdev, lstart, start, len);
+
+ rb_link_node(&dc->rb_node, parent, p);
+ rb_insert_color_cached(&dc->rb_node, &dcc->root, leftmost);
}
static void __relocate_discard_cmd(struct discard_cmd_control *dcc,
struct discard_cmd *dc)
{
- list_move_tail(&dc->list, &dcc->pend_list[plist_idx(dc->len)]);
+ list_move_tail(&dc->list, &dcc->pend_list[plist_idx(dc->di.len)]);
}
static void __punch_discard_cmd(struct f2fs_sb_info *sbi,
@@ -1244,7 +1342,7 @@ static void __punch_discard_cmd(struct f2fs_sb_info *sbi,
struct discard_info di = dc->di;
bool modified = false;
- if (dc->state == D_DONE || dc->len == 1) {
+ if (dc->state == D_DONE || dc->di.len == 1) {
__remove_discard_cmd(sbi, dc);
return;
}
@@ -1252,23 +1350,22 @@ static void __punch_discard_cmd(struct f2fs_sb_info *sbi,
dcc->undiscard_blks -= di.len;
if (blkaddr > di.lstart) {
- dc->len = blkaddr - dc->lstart;
- dcc->undiscard_blks += dc->len;
+ dc->di.len = blkaddr - dc->di.lstart;
+ dcc->undiscard_blks += dc->di.len;
__relocate_discard_cmd(dcc, dc);
modified = true;
}
if (blkaddr < di.lstart + di.len - 1) {
if (modified) {
- __insert_discard_tree(sbi, dc->bdev, blkaddr + 1,
+ __insert_discard_cmd(sbi, dc->bdev, blkaddr + 1,
di.start + blkaddr + 1 - di.lstart,
- di.lstart + di.len - 1 - blkaddr,
- NULL, NULL);
+ di.lstart + di.len - 1 - blkaddr);
} else {
- dc->lstart++;
- dc->len--;
- dc->start++;
- dcc->undiscard_blks += dc->len;
+ dc->di.lstart++;
+ dc->di.len--;
+ dc->di.start++;
+ dcc->undiscard_blks += dc->di.len;
__relocate_discard_cmd(dcc, dc);
}
}
@@ -1287,37 +1384,33 @@ static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
SECTOR_TO_BLOCK(bdev_max_discard_sectors(bdev));
block_t end = lstart + len;
- dc = (struct discard_cmd *)f2fs_lookup_rb_tree_ret(&dcc->root,
- NULL, lstart,
- (struct rb_entry **)&prev_dc,
- (struct rb_entry **)&next_dc,
- &insert_p, &insert_parent, true, NULL);
+ dc = __lookup_discard_cmd_ret(&dcc->root, lstart,
+ &prev_dc, &next_dc, &insert_p, &insert_parent);
if (dc)
prev_dc = dc;
if (!prev_dc) {
di.lstart = lstart;
- di.len = next_dc ? next_dc->lstart - lstart : len;
+ di.len = next_dc ? next_dc->di.lstart - lstart : len;
di.len = min(di.len, len);
di.start = start;
}
while (1) {
struct rb_node *node;
- bool merged = false;
struct discard_cmd *tdc = NULL;
if (prev_dc) {
- di.lstart = prev_dc->lstart + prev_dc->len;
+ di.lstart = prev_dc->di.lstart + prev_dc->di.len;
if (di.lstart < lstart)
di.lstart = lstart;
if (di.lstart >= end)
break;
- if (!next_dc || next_dc->lstart > end)
+ if (!next_dc || next_dc->di.lstart > end)
di.len = end - di.lstart;
else
- di.len = next_dc->lstart - di.lstart;
+ di.len = next_dc->di.lstart - di.lstart;
di.start = start + di.lstart - lstart;
}
@@ -1333,7 +1426,7 @@ static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
__relocate_discard_cmd(dcc, prev_dc);
di = prev_dc->di;
tdc = prev_dc;
- merged = true;
+ goto next;
}
if (next_dc && next_dc->state == D_PREP &&
@@ -1347,13 +1440,10 @@ static void __update_discard_tree_range(struct f2fs_sb_info *sbi,
__relocate_discard_cmd(dcc, next_dc);
if (tdc)
__remove_discard_cmd(sbi, tdc);
- merged = true;
+ goto next;
}
- if (!merged) {
- __insert_discard_tree(sbi, bdev, di.lstart, di.start,
- di.len, NULL, NULL);
- }
+ __insert_discard_cmd(sbi, bdev, di.lstart, di.start, di.len);
next:
prev_dc = next_dc;
if (!prev_dc)
@@ -1392,15 +1482,11 @@ static void __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
struct rb_node **insert_p = NULL, *insert_parent = NULL;
struct discard_cmd *dc;
struct blk_plug plug;
- unsigned int pos = dcc->next_pos;
bool io_interrupted = false;
mutex_lock(&dcc->cmd_lock);
- dc = (struct discard_cmd *)f2fs_lookup_rb_tree_ret(&dcc->root,
- NULL, pos,
- (struct rb_entry **)&prev_dc,
- (struct rb_entry **)&next_dc,
- &insert_p, &insert_parent, true, NULL);
+ dc = __lookup_discard_cmd_ret(&dcc->root, dcc->next_pos,
+ &prev_dc, &next_dc, &insert_p, &insert_parent);
if (!dc)
dc = next_dc;
@@ -1418,7 +1504,7 @@ static void __issue_discard_cmd_orderly(struct f2fs_sb_info *sbi,
break;
}
- dcc->next_pos = dc->lstart + dc->len;
+ dcc->next_pos = dc->di.lstart + dc->di.len;
err = __submit_discard_cmd(sbi, dpolicy, dc, issued);
if (*issued >= dpolicy->max_requests)
@@ -1477,8 +1563,7 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
if (list_empty(pend_list))
goto next;
if (unlikely(dcc->rbtree_check))
- f2fs_bug_on(sbi, !f2fs_check_rb_tree_consistence(sbi,
- &dcc->root));
+ f2fs_bug_on(sbi, !f2fs_check_discard_tree(sbi));
blk_start_plug(&plug);
list_for_each_entry_safe(dc, tmp, pend_list, list) {
f2fs_bug_on(sbi, dc->state != D_PREP);
@@ -1556,7 +1641,7 @@ static unsigned int __wait_one_discard_bio(struct f2fs_sb_info *sbi,
dc->ref--;
if (!dc->ref) {
if (!dc->error)
- len = dc->len;
+ len = dc->di.len;
__remove_discard_cmd(sbi, dc);
}
mutex_unlock(&dcc->cmd_lock);
@@ -1579,14 +1664,15 @@ static unsigned int __wait_discard_cmd_range(struct f2fs_sb_info *sbi,
mutex_lock(&dcc->cmd_lock);
list_for_each_entry_safe(iter, tmp, wait_list, list) {
- if (iter->lstart + iter->len <= start || end <= iter->lstart)
+ if (iter->di.lstart + iter->di.len <= start ||
+ end <= iter->di.lstart)
continue;
- if (iter->len < dpolicy->granularity)
+ if (iter->di.len < dpolicy->granularity)
continue;
if (iter->state == D_DONE && !iter->ref) {
wait_for_completion_io(&iter->wait);
if (!iter->error)
- trimmed += iter->len;
+ trimmed += iter->di.len;
__remove_discard_cmd(sbi, iter);
} else {
iter->ref++;
@@ -1630,8 +1716,7 @@ static void f2fs_wait_discard_bio(struct f2fs_sb_info *sbi, block_t blkaddr)
bool need_wait = false;
mutex_lock(&dcc->cmd_lock);
- dc = (struct discard_cmd *)f2fs_lookup_rb_tree(&dcc->root,
- NULL, blkaddr);
+ dc = __lookup_discard_cmd(sbi, blkaddr);
if (dc) {
if (dc->state == D_PREP) {
__punch_discard_cmd(sbi, dc, blkaddr);
@@ -2964,24 +3049,20 @@ static unsigned int __issue_discard_cmd_range(struct f2fs_sb_info *sbi,
mutex_lock(&dcc->cmd_lock);
if (unlikely(dcc->rbtree_check))
- f2fs_bug_on(sbi, !f2fs_check_rb_tree_consistence(sbi,
- &dcc->root));
-
- dc = (struct discard_cmd *)f2fs_lookup_rb_tree_ret(&dcc->root,
- NULL, start,
- (struct rb_entry **)&prev_dc,
- (struct rb_entry **)&next_dc,
- &insert_p, &insert_parent, true, NULL);
+ f2fs_bug_on(sbi, !f2fs_check_discard_tree(sbi));
+
+ dc = __lookup_discard_cmd_ret(&dcc->root, start,
+ &prev_dc, &next_dc, &insert_p, &insert_parent);
if (!dc)
dc = next_dc;
blk_start_plug(&plug);
- while (dc && dc->lstart <= end) {
+ while (dc && dc->di.lstart <= end) {
struct rb_node *node;
int err = 0;
- if (dc->len < dpolicy->granularity)
+ if (dc->di.len < dpolicy->granularity)
goto skip;
if (dc->state != D_PREP) {
@@ -2992,7 +3073,7 @@ static unsigned int __issue_discard_cmd_range(struct f2fs_sb_info *sbi,
err = __submit_discard_cmd(sbi, dpolicy, dc, &issued);
if (issued >= dpolicy->max_requests) {
- start = dc->lstart + dc->len;
+ start = dc->di.lstart + dc->di.len;
if (err)
__remove_discard_cmd(sbi, dc);
--
2.40.0.rc1.284.g88254d51c5-goog
On Fri, Mar 10, 2023 at 01:04:53PM -0800, Jaegeuk Kim wrote:
> +static bool f2fs_check_discard_tree(struct f2fs_sb_info *sbi)
> +{
> +#ifdef CONFIG_F2FS_CHECK_FS
> + struct discard_cmd_control *dcc = SM_I(sbi)->dcc_info;
> + struct rb_node *cur = rb_first_cached(&dcc->root), *next;
> + struct discard_cmd *cur_dc, *next_dc;
> +
> + if (!cur)
> + return true;
> +
> + while (cur) {
The !cur check is redundant here.
- Eric