[RFC PATCH v4 13/15] dcache: Provide a dentry constructor

Tobin C. Harding
2019-04-30T03:10:31Z

In order to support object migration on the dentry cache we need to have
a determined object state at all times. Without a constructor the object
would have a random state after allocation.

Provide a dentry constructor.

Signed-off-by: Tobin C. Harding <tobin@kernel.org>
---
fs/dcache.c | 30 +++++++++++++++++++++---------
1 file changed, 21 insertions(+), 9 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index aac41adf4743..3d6cc06eca56 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1603,6 +1603,16 @@ void d_invalidate(struct dentry *dentry)
}
EXPORT_SYMBOL(d_invalidate);

+static void dcache_ctor(void *p)
+{
+ struct dentry *dentry = p;
+
+ /* Mimic lockref_mark_dead() */
+ dentry->d_lockref.count = -128;
+
+ spin_lock_init(&dentry->d_lock);
+}
+
/**
* __d_alloc - allocate a dcache entry
* @sb: filesystem it will belong to
@@ -1658,7 +1668,6 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)

dentry->d_lockref.count = 1;
dentry->d_flags = 0;
- spin_lock_init(&dentry->d_lock);
seqcount_init(&dentry->d_seq);
dentry->d_inode = NULL;
dentry->d_parent = dentry;
@@ -3091,14 +3100,17 @@ static void __init dcache_init_early(void)

static void __init dcache_init(void)
{
- /*
- * A constructor could be added for stable state like the lists,
- * but it is probably not worth it because of the cache nature
- * of the dcache.
- */
- dentry_cache = KMEM_CACHE_USERCOPY(dentry,
- SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|SLAB_MEM_SPREAD|SLAB_ACCOUNT,
- d_iname);
+ slab_flags_t flags =
+ SLAB_RECLAIM_ACCOUNT | SLAB_PANIC | SLAB_MEM_SPREAD | SLAB_ACCOUNT;
+
+ dentry_cache =
+ kmem_cache_create_usercopy("dentry",
+ sizeof(struct dentry),
+ __alignof__(struct dentry),
+ flags,
+ offsetof(struct dentry, d_iname),
+ sizeof_field(struct dentry, d_iname),
+ dcache_ctor);

/* Hash may have been set up in dcache_init_early */
if (!hashdist)
--
2.21.0