[PATCH v3 03/21] dentry: switch the lists of children to hlist

From: Al Viro
Date: Fri Nov 24 2023 - 01:05:27 EST

Saves a pointer per struct dentry and actually makes the things less
clumsy. Cleaned the d_walk() and dcache_readdir() a bit by use
of hlist_for_... iterators.

A couple of new helpers - d_first_child() and d_next_sibling(),
to make the expressions less awful.

X-fuck-kABI: gladly
Reviewed-by: Christian Brauner <brauner@xxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
Documentation/filesystems/porting.rst | 9 +++
arch/powerpc/platforms/cell/spufs/inode.c | 5 +-
fs/afs/dynroot.c | 5 +-
fs/autofs/expire.c | 7 +--
fs/ceph/dir.c | 2 +-
fs/ceph/mds_client.c | 2 +-
fs/coda/cache.c | 2 +-
fs/dcache.c | 76 +++++++++++------------
fs/libfs.c | 45 +++++++-------
fs/notify/fsnotify.c | 2 +-
fs/tracefs/inode.c | 34 +++++-----
include/linux/dcache.h | 20 ++++--
12 files changed, 108 insertions(+), 101 deletions(-)

diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst
index 878e72b2f8b7..331405f4b29f 100644
--- a/Documentation/filesystems/porting.rst
+++ b/Documentation/filesystems/porting.rst
@@ -1061,3 +1061,12 @@ export_operations ->encode_fh() no longer has a default implementation to
encode FILEID_INO32_GEN* file handles.
Filesystems that used the default implementation may use the generic helper
generic_encode_ino32_fh() explicitly.
+
+---
+
+**mandatory**
+
+The list of children anchored in parent dentry got turned into hlist now.
+Field names got changed (->d_children/->d_sib instead of ->d_subdirs/->d_child
+for anchor/entries resp.), so any affected places will be immediately caught
+by compiler.
diff --git a/arch/powerpc/platforms/cell/spufs/inode.c b/arch/powerpc/platforms/cell/spufs/inode.c
index 10c1320adfd0..030de2b8c145 100644
--- a/arch/powerpc/platforms/cell/spufs/inode.c
+++ b/arch/powerpc/platforms/cell/spufs/inode.c
@@ -145,10 +145,11 @@ spufs_evict_inode(struct inode *inode)

static void spufs_prune_dir(struct dentry *dir)
{
- struct dentry *dentry, *tmp;
+ struct dentry *dentry;
+ struct hlist_node *n;

inode_lock(d_inode(dir));
- list_for_each_entry_safe(dentry, tmp, &dir->d_subdirs, d_child) {
+ hlist_for_each_entry_safe(dentry, n, &dir->d_children, d_sib) {
spin_lock(&dentry->d_lock);
if (simple_positive(dentry)) {
dget_dlock(dentry);
diff --git a/fs/afs/dynroot.c b/fs/afs/dynroot.c
index 4d04ef2d3ae7..fe45462834cc 100644
--- a/fs/afs/dynroot.c
+++ b/fs/afs/dynroot.c
@@ -370,7 +370,7 @@ int afs_dynroot_populate(struct super_block *sb)
void afs_dynroot_depopulate(struct super_block *sb)
{
struct afs_net *net = afs_sb2net(sb);
- struct dentry *root = sb->s_root, *subdir, *tmp;
+ struct dentry *root = sb->s_root, *subdir;

/* Prevent more subdirs from being created */
mutex_lock(&net->proc_cells_lock);
@@ -379,10 +379,11 @@ void afs_dynroot_depopulate(struct super_block *sb)
mutex_unlock(&net->proc_cells_lock);

if (root) {
+ struct hlist_node *n;
inode_lock(root->d_inode);

/* Remove all the pins for dirs created for manually added cells */
- list_for_each_entry_safe(subdir, tmp, &root->d_subdirs, d_child) {
+ hlist_for_each_entry_safe(subdir, n, &root->d_children, d_sib) {
if (subdir->d_fsdata) {
subdir->d_fsdata = NULL;
dput(subdir);
diff --git a/fs/autofs/expire.c b/fs/autofs/expire.c
index 038b3d2d9f57..39d8c84c16f4 100644
--- a/fs/autofs/expire.c
+++ b/fs/autofs/expire.c
@@ -73,12 +73,9 @@ static int autofs_mount_busy(struct vfsmount *mnt,
/* p->d_lock held */
static struct dentry *positive_after(struct dentry *p, struct dentry *child)
{
- if (child)
- child = list_next_entry(child, d_child);
- else
- child = list_first_entry(&p->d_subdirs, struct dentry, d_child);
+ child = child ? d_next_sibling(child) : d_first_child(p);

- list_for_each_entry_from(child, &p->d_subdirs, d_child) {
+ hlist_for_each_entry_from(child, d_sib) {
spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
if (simple_positive(child)) {
dget_dlock(child);
diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
index 91709934c8b1..678596684596 100644
--- a/fs/ceph/dir.c
+++ b/fs/ceph/dir.c
@@ -174,7 +174,7 @@ __dcache_find_get_entry(struct dentry *parent, u64 idx,
/*
* When possible, we try to satisfy a readdir by peeking at the
* dcache. We make this work by carefully ordering dentries on
- * d_child when we initially get results back from the MDS, and
+ * d_children when we initially get results back from the MDS, and
* falling back to a "normal" sync readdir if any dentries in the dir
* are dropped.
*
diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c
index d95eb525519a..02ebfabfc8ee 100644
--- a/fs/ceph/mds_client.c
+++ b/fs/ceph/mds_client.c
@@ -2128,7 +2128,7 @@ static bool drop_negative_children(struct dentry *dentry)
goto out;

spin_lock(&dentry->d_lock);
- list_for_each_entry(child, &dentry->d_subdirs, d_child) {
+ hlist_for_each_entry(child, &dentry->d_children, d_sib) {
if (d_really_is_positive(child)) {
all_negative = false;
break;
diff --git a/fs/coda/cache.c b/fs/coda/cache.c
index bfbc03c6b632..f5b71a35f9db 100644
--- a/fs/coda/cache.c
+++ b/fs/coda/cache.c
@@ -94,7 +94,7 @@ static void coda_flag_children(struct dentry *parent, int flag)

rcu_read_lock();
spin_lock(&parent->d_lock);
- list_for_each_entry(de, &parent->d_subdirs, d_child) {
+ hlist_for_each_entry(de, &parent->d_children, d_sib) {
struct inode *inode = d_inode_rcu(de);
/* don't know what to do with negative dentries */
if (inode)
diff --git a/fs/dcache.c b/fs/dcache.c
index c82ae731df9a..59f76c9a15d1 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -51,8 +51,8 @@
* - d_lru
* - d_count
* - d_unhashed()
- * - d_parent and d_subdirs
- * - childrens' d_child and d_parent
+ * - d_parent and d_chilren
+ * - childrens' d_sib and d_parent
* - d_u.d_alias, d_inode
*
* Ordering:
@@ -537,7 +537,7 @@ void d_drop(struct dentry *dentry)
}
EXPORT_SYMBOL(d_drop);

-static inline void dentry_unlist(struct dentry *dentry, struct dentry *parent)
+static inline void dentry_unlist(struct dentry *dentry)
{
struct dentry *next;
/*
@@ -545,12 +545,12 @@ static inline void dentry_unlist(struct dentry *dentry, struct dentry *parent)
* attached to the dentry tree
*/
dentry->d_flags |= DCACHE_DENTRY_KILLED;
- if (unlikely(list_empty(&dentry->d_child)))
+ if (unlikely(hlist_unhashed(&dentry->d_sib)))
return;
- __list_del_entry(&dentry->d_child);
+ __hlist_del(&dentry->d_sib);
/*
* Cursors can move around the list of children. While we'd been
- * a normal list member, it didn't matter - ->d_child.next would've
+ * a normal list member, it didn't matter - ->d_sib.next would've
* been updated. However, from now on it won't be and for the
* things like d_walk() it might end up with a nasty surprise.
* Normally d_walk() doesn't care about cursors moving around -
@@ -558,20 +558,20 @@ static inline void dentry_unlist(struct dentry *dentry, struct dentry *parent)
* of its own, we get through it without ever unlocking the parent.
* There is one exception, though - if we ascend from a child that
* gets killed as soon as we unlock it, the next sibling is found
- * using the value left in its ->d_child.next. And if _that_
+ * using the value left in its ->d_sib.next. And if _that_
* pointed to a cursor, and cursor got moved (e.g. by lseek())
* before d_walk() regains parent->d_lock, we'll end up skipping
* everything the cursor had been moved past.
*
- * Solution: make sure that the pointer left behind in ->d_child.next
+ * Solution: make sure that the pointer left behind in ->d_sib.next
* points to something that won't be moving around. I.e. skip the
* cursors.
*/
- while (dentry->d_child.next != &parent->d_subdirs) {
- next = list_entry(dentry->d_child.next, struct dentry, d_child);
+ while (dentry->d_sib.next) {
+ next = hlist_entry(dentry->d_sib.next, struct dentry, d_sib);
if (likely(!(next->d_flags & DCACHE_DENTRY_CURSOR)))
break;
- dentry->d_child.next = next->d_child.next;
+ dentry->d_sib.next = next->d_sib.next;
}
}

@@ -600,7 +600,7 @@ static void __dentry_kill(struct dentry *dentry)
}
/* if it was on the hash then remove it */
__d_drop(dentry);
- dentry_unlist(dentry, parent);
+ dentry_unlist(dentry);
if (parent)
spin_unlock(&parent->d_lock);
if (dentry->d_inode)
@@ -1348,8 +1348,7 @@ enum d_walk_ret {
static void d_walk(struct dentry *parent, void *data,
enum d_walk_ret (*enter)(void *, struct dentry *))
{
- struct dentry *this_parent;
- struct list_head *next;
+ struct dentry *this_parent, *dentry;
unsigned seq = 0;
enum d_walk_ret ret;
bool retry = true;
@@ -1371,13 +1370,9 @@ static void d_walk(struct dentry *parent, void *data,
break;
}
repeat:
- next = this_parent->d_subdirs.next;
+ dentry = d_first_child(this_parent);
resume:
- while (next != &this_parent->d_subdirs) {
- struct list_head *tmp = next;
- struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
- next = tmp->next;
-
+ hlist_for_each_entry_from(dentry, d_sib) {
if (unlikely(dentry->d_flags & DCACHE_DENTRY_CURSOR))
continue;

@@ -1398,7 +1393,7 @@ static void d_walk(struct dentry *parent, void *data,
continue;
}

- if (!list_empty(&dentry->d_subdirs)) {
+ if (!hlist_empty(&dentry->d_children)) {
spin_unlock(&this_parent->d_lock);
spin_release(&dentry->d_lock.dep_map, _RET_IP_);
this_parent = dentry;
@@ -1413,24 +1408,23 @@ static void d_walk(struct dentry *parent, void *data,
rcu_read_lock();
ascend:
if (this_parent != parent) {
- struct dentry *child = this_parent;
- this_parent = child->d_parent;
+ dentry = this_parent;
+ this_parent = dentry->d_parent;

- spin_unlock(&child->d_lock);
+ spin_unlock(&dentry->d_lock);
spin_lock(&this_parent->d_lock);

/* might go back up the wrong parent if we have had a rename. */
if (need_seqretry(&rename_lock, seq))
goto rename_retry;
/* go into the first sibling still alive */
- do {
- next = child->d_child.next;
- if (next == &this_parent->d_subdirs)
- goto ascend;
- child = list_entry(next, struct dentry, d_child);
- } while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
- rcu_read_unlock();
- goto resume;
+ hlist_for_each_entry_continue(dentry, d_sib) {
+ if (likely(!(dentry->d_flags & DCACHE_DENTRY_KILLED))) {
+ rcu_read_unlock();
+ goto resume;
+ }
+ }
+ goto ascend;
}
if (need_seqretry(&rename_lock, seq))
goto rename_retry;
@@ -1530,7 +1524,7 @@ int d_set_mounted(struct dentry *dentry)
* Search the dentry child list of the specified parent,
* and move any unused dentries to the end of the unused
* list for prune_dcache(). We descend to the next level
- * whenever the d_subdirs list is non-empty and continue
+ * whenever the d_children list is non-empty and continue
* searching.
*
* It returns zero iff there are no unused children,
@@ -1657,7 +1651,7 @@ EXPORT_SYMBOL(shrink_dcache_parent);
static enum d_walk_ret umount_check(void *_data, struct dentry *dentry)
{
/* it has busy descendents; complain about those instead */
- if (!list_empty(&dentry->d_subdirs))
+ if (!hlist_empty(&dentry->d_children))
return D_WALK_CONTINUE;

/* root with refcount 1 is fine */
@@ -1814,9 +1808,9 @@ static struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
dentry->d_fsdata = NULL;
INIT_HLIST_BL_NODE(&dentry->d_hash);
INIT_LIST_HEAD(&dentry->d_lru);
- INIT_LIST_HEAD(&dentry->d_subdirs);
+ INIT_HLIST_HEAD(&dentry->d_children);
INIT_HLIST_NODE(&dentry->d_u.d_alias);
- INIT_LIST_HEAD(&dentry->d_child);
+ INIT_HLIST_NODE(&dentry->d_sib);
d_set_d_op(dentry, dentry->d_sb->s_d_op);

if (dentry->d_op && dentry->d_op->d_init) {
@@ -1855,7 +1849,7 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
*/
__dget_dlock(parent);
dentry->d_parent = parent;
- list_add(&dentry->d_child, &parent->d_subdirs);
+ hlist_add_head(&dentry->d_sib, &parent->d_children);
spin_unlock(&parent->d_lock);

return dentry;
@@ -2993,11 +2987,15 @@ static void __d_move(struct dentry *dentry, struct dentry *target,
} else {
target->d_parent = old_parent;
swap_names(dentry, target);
- list_move(&target->d_child, &target->d_parent->d_subdirs);
+ if (!hlist_unhashed(&target->d_sib))
+ __hlist_del(&target->d_sib);
+ hlist_add_head(&target->d_sib, &target->d_parent->d_children);
__d_rehash(target);
fsnotify_update_flags(target);
}
- list_move(&dentry->d_child, &dentry->d_parent->d_subdirs);
+ if (!hlist_unhashed(&dentry->d_sib))
+ __hlist_del(&dentry->d_sib);
+ hlist_add_head(&dentry->d_sib, &dentry->d_parent->d_children);
__d_rehash(dentry);
fsnotify_update_flags(dentry);
fscrypt_handle_d_move(dentry);
diff --git a/fs/libfs.c b/fs/libfs.c
index e9440d55073c..46c9177769c1 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -104,15 +104,16 @@ EXPORT_SYMBOL(dcache_dir_close);
* If no such element exists, NULL is returned.
*/
static struct dentry *scan_positives(struct dentry *cursor,
- struct list_head *p,
+ struct hlist_node **p,
loff_t count,
struct dentry *last)
{
struct dentry *dentry = cursor->d_parent, *found = NULL;

spin_lock(&dentry->d_lock);
- while ((p = p->next) != &dentry->d_subdirs) {
- struct dentry *d = list_entry(p, struct dentry, d_child);
+ while (*p) {
+ struct dentry *d = hlist_entry(*p, struct dentry, d_sib);
+ p = &d->d_sib.next;
// we must at least skip cursors, to avoid livelocks
if (d->d_flags & DCACHE_DENTRY_CURSOR)
continue;
@@ -126,8 +127,10 @@ static struct dentry *scan_positives(struct dentry *cursor,
count = 1;
}
if (need_resched()) {
- list_move(&cursor->d_child, p);
- p = &cursor->d_child;
+ if (!hlist_unhashed(&cursor->d_sib))
+ __hlist_del(&cursor->d_sib);
+ hlist_add_behind(&cursor->d_sib, &d->d_sib);
+ p = &cursor->d_sib.next;
spin_unlock(&dentry->d_lock);
cond_resched();
spin_lock(&dentry->d_lock);
@@ -159,13 +162,12 @@ loff_t dcache_dir_lseek(struct file *file, loff_t offset, int whence)
inode_lock_shared(dentry->d_inode);

if (offset > 2)
- to = scan_positives(cursor, &dentry->d_subdirs,
+ to = scan_positives(cursor, &dentry->d_children.first,
offset - 2, NULL);
spin_lock(&dentry->d_lock);
+ hlist_del_init(&cursor->d_sib);
if (to)
- list_move(&cursor->d_child, &to->d_child);
- else
- list_del_init(&cursor->d_child);
+ hlist_add_behind(&cursor->d_sib, &to->d_sib);
spin_unlock(&dentry->d_lock);
dput(to);

@@ -187,19 +189,16 @@ int dcache_readdir(struct file *file, struct dir_context *ctx)
{
struct dentry *dentry = file->f_path.dentry;
struct dentry *cursor = file->private_data;
- struct list_head *anchor = &dentry->d_subdirs;
struct dentry *next = NULL;
- struct list_head *p;
+ struct hlist_node **p;

if (!dir_emit_dots(file, ctx))
return 0;

if (ctx->pos == 2)
- p = anchor;
- else if (!list_empty(&cursor->d_child))
- p = &cursor->d_child;
+ p = &dentry->d_children.first;
else
- return 0;
+ p = &cursor->d_sib.next;

while ((next = scan_positives(cursor, p, 1, next)) != NULL) {
if (!dir_emit(ctx, next->d_name.name, next->d_name.len,
@@ -207,13 +206,12 @@ int dcache_readdir(struct file *file, struct dir_context *ctx)
fs_umode_to_dtype(d_inode(next)->i_mode)))
break;
ctx->pos++;
- p = &next->d_child;
+ p = &next->d_sib.next;
}
spin_lock(&dentry->d_lock);
+ hlist_del_init(&cursor->d_sib);
if (next)
- list_move_tail(&cursor->d_child, &next->d_child);
- else
- list_del_init(&cursor->d_child);
+ hlist_add_before(&cursor->d_sib, &next->d_sib);
spin_unlock(&dentry->d_lock);
dput(next);

@@ -492,12 +490,11 @@ const struct file_operations simple_offset_dir_operations = {

static struct dentry *find_next_child(struct dentry *parent, struct dentry *prev)
{
- struct dentry *child = NULL;
- struct list_head *p = prev ? &prev->d_child : &parent->d_subdirs;
+ struct dentry *child = NULL, *d;

spin_lock(&parent->d_lock);
- while ((p = p->next) != &parent->d_subdirs) {
- struct dentry *d = container_of(p, struct dentry, d_child);
+ d = prev ? d_next_sibling(prev) : d_first_child(parent);
+ hlist_for_each_entry_from(d, d_sib) {
if (simple_positive(d)) {
spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED);
if (simple_positive(d))
@@ -658,7 +655,7 @@ int simple_empty(struct dentry *dentry)
int ret = 0;

spin_lock(&dentry->d_lock);
- list_for_each_entry(child, &dentry->d_subdirs, d_child) {
+ hlist_for_each_entry(child, &dentry->d_children, d_sib) {
spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
if (simple_positive(child)) {
spin_unlock(&child->d_lock);
diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 7974e91ffe13..8bfd690e9f10 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -124,7 +124,7 @@ void __fsnotify_update_child_dentry_flags(struct inode *inode)
* d_flags to indicate parental interest (their parent is the
* original inode) */
spin_lock(&alias->d_lock);
- list_for_each_entry(child, &alias->d_subdirs, d_child) {
+ hlist_for_each_entry(child, &alias->d_children, d_sib) {
if (!child->d_inode)
continue;

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index 5b54948514fe..61ca5fcf10f9 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -199,26 +199,21 @@ static void change_gid(struct dentry *dentry, kgid_t gid)
*/
static void set_gid(struct dentry *parent, kgid_t gid)
{
- struct dentry *this_parent;
- struct list_head *next;
+ struct dentry *this_parent, *dentry;

this_parent = parent;
spin_lock(&this_parent->d_lock);

change_gid(this_parent, gid);
repeat:
- next = this_parent->d_subdirs.next;
+ dentry = d_first_child(this_parent);
resume:
- while (next != &this_parent->d_subdirs) {
- struct list_head *tmp = next;
- struct dentry *dentry = list_entry(tmp, struct dentry, d_child);
- next = tmp->next;
-
+ hlist_for_each_entry_from(dentry, d_sib) {
spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);

change_gid(dentry, gid);

- if (!list_empty(&dentry->d_subdirs)) {
+ if (!hlist_empty(&dentry->d_children)) {
spin_unlock(&this_parent->d_lock);
spin_release(&dentry->d_lock.dep_map, _RET_IP_);
this_parent = dentry;
@@ -233,21 +228,20 @@ static void set_gid(struct dentry *parent, kgid_t gid)
rcu_read_lock();
ascend:
if (this_parent != parent) {
- struct dentry *child = this_parent;
- this_parent = child->d_parent;
+ dentry = this_parent;
+ this_parent = dentry->d_parent;

- spin_unlock(&child->d_lock);
+ spin_unlock(&dentry->d_lock);
spin_lock(&this_parent->d_lock);

/* go into the first sibling still alive */
- do {
- next = child->d_child.next;
- if (next == &this_parent->d_subdirs)
- goto ascend;
- child = list_entry(next, struct dentry, d_child);
- } while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED));
- rcu_read_unlock();
- goto resume;
+ hlist_for_each_entry_continue(dentry, d_sib) {
+ if (likely(!(dentry->d_flags & DCACHE_DENTRY_KILLED))) {
+ rcu_read_unlock();
+ goto resume;
+ }
+ }
+ goto ascend;
}
rcu_read_unlock();
spin_unlock(&this_parent->d_lock);
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 3da2f0545d5d..0e397a0c519c 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -68,12 +68,12 @@ extern const struct qstr dotdot_name;
* large memory footprint increase).
*/
#ifdef CONFIG_64BIT
-# define DNAME_INLINE_LEN 32 /* 192 bytes */
+# define DNAME_INLINE_LEN 40 /* 192 bytes */
#else
# ifdef CONFIG_SMP
-# define DNAME_INLINE_LEN 36 /* 128 bytes */
-# else
# define DNAME_INLINE_LEN 40 /* 128 bytes */
+# else
+# define DNAME_INLINE_LEN 44 /* 128 bytes */
# endif
#endif

@@ -101,8 +101,8 @@ struct dentry {
struct list_head d_lru; /* LRU list */
wait_queue_head_t *d_wait; /* in-lookup ones only */
};
- struct list_head d_child; /* child of parent list */
- struct list_head d_subdirs; /* our children */
+ struct hlist_node d_sib; /* child of parent list */
+ struct hlist_head d_children; /* our children */
/*
* d_alias and d_rcu can share memory
*/
@@ -600,4 +600,14 @@ struct name_snapshot {
void take_dentry_name_snapshot(struct name_snapshot *, struct dentry *);
void release_dentry_name_snapshot(struct name_snapshot *);

+static inline struct dentry *d_first_child(const struct dentry *dentry)
+{
+ return hlist_entry_safe(dentry->d_children.first, struct dentry, d_sib);
+}
+
+static inline struct dentry *d_next_sibling(const struct dentry *dentry)
+{
+ return hlist_entry_safe(dentry->d_sib.next, struct dentry, d_sib);
+}
+
#endif /* __LINUX_DCACHE_H */
--
2.39.2