mirrors/linux
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2025-12-27 11:06:41 -05:00
Code Issues Packages Projects Releases Wiki Activity

dissolve external_name.u into separate members

Browse Source 
... and document the constraints on the layout.  Kept separate from
the previous commit to keep the noise separate from actual changes.
The reason for explicit __aligned() on ->name[] rather than relying
upon the alignment of the previous field is that the previous iteration
of that commit tried to save 4 bytes on 64bit by eliminating a hole
in there, which broke the assumptions in dentry_string_cmp().
Better spell it out and avoid the temptation for the future...

Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
2024-12-09 20:03:33 -05:00
parent 1c9be84a90
commit 95a4ccbbe5
1 changed files with 17 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

30
fs/dcache.c
View File

@@ -295,12 +295,16 @@ static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *c
return dentry_string_cmp(cs, ct, tcount);
}
/*
* long names are allocated separately from dentry and never modified.
* Refcounted, freeing is RCU-delayed. See take_dentry_name_snapshot()
* for the reason why ->count and ->head can't be combined into a union.
* dentry_string_cmp() relies upon ->name[] being word-aligned.
*/
struct external_name {
struct {
atomic_t count; // ->count and ->head can't be combined
struct rcu_head head; // see take_dentry_name_snapshot()
} u;
unsigned char name[];
atomic_t count;
struct rcu_head head;
unsigned char name[] __aligned(sizeof(unsigned long));
};
static inline struct external_name *external_name(struct dentry *dentry)
@@ -344,7 +348,7 @@ void take_dentry_name_snapshot(struct name_snapshot *name, struct dentry *dentry
struct external_name *p;
p = container_of(s, struct external_name, name[0]);
// get a valid reference
if (unlikely(!atomic_inc_not_zero(&p->u.count)))
if (unlikely(!atomic_inc_not_zero(&p->count)))
goto retry;
name->name.name = s;
}
@@ -361,8 +365,8 @@ void release_dentry_name_snapshot(struct name_snapshot *name)
if (unlikely(name->name.name != name->inline_name.string)) {
struct external_name *p;
p = container_of(name->name.name, struct external_name, name[0]);
if (unlikely(atomic_dec_and_test(&p->u.count)))
kfree_rcu(p, u.head);
if (unlikely(atomic_dec_and_test(&p->count)))
kfree_rcu(p, head);
}
}
EXPORT_SYMBOL(release_dentry_name_snapshot);
@@ -400,7 +404,7 @@ static void dentry_free(struct dentry *dentry)
WARN_ON(!hlist_unhashed(&dentry->d_u.d_alias));
if (unlikely(dname_external(dentry))) {
struct external_name *p = external_name(dentry);
if (likely(atomic_dec_and_test(&p->u.count))) {
if (likely(atomic_dec_and_test(&p->count))) {
call_rcu(&dentry->d_u.d_rcu, __d_free_external);
return;
}
@@ -1681,7 +1685,7 @@ static struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
kmem_cache_free(dentry_cache, dentry);
return NULL;
}
atomic_set(&p->u.count, 1);
atomic_set(&p->count, 1);
dname = p->name;
} else {
dname = dentry->d_shortname.string;
@@ -2774,15 +2778,15 @@ static void copy_name(struct dentry *dentry, struct dentry *target)
if (unlikely(dname_external(dentry)))
old_name = external_name(dentry);
if (unlikely(dname_external(target))) {
atomic_inc(&external_name(target)->u.count);
atomic_inc(&external_name(target)->count);
dentry->d_name = target->d_name;
} else {
dentry->d_shortname = target->d_shortname;
dentry->d_name.name = dentry->d_shortname.string;
dentry->d_name.hash_len = target->d_name.hash_len;
}
if (old_name && likely(atomic_dec_and_test(&old_name->u.count)))
kfree_rcu(old_name, u.head);
if (old_name && likely(atomic_dec_and_test(&old_name->count)))
kfree_rcu(old_name, head);
}
/*