linux-kernel - [RFC PATCH v3 13/15] dcache: Provide a dentry constructor

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Date:   Thu, 11 Apr 2019 11:34:39 +1000
From:   "Tobin C. Harding" <tobin@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     "Tobin C. Harding" <tobin@...nel.org>,
        Roman Gushchin <guro@...com>,
        Alexander Viro <viro@....linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Pekka Enberg <penberg@...helsinki.fi>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Christopher Lameter <cl@...ux.com>,
        Matthew Wilcox <willy@...radead.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Andreas Dilger <adilger@...ger.ca>,
        Waiman Long <longman@...hat.com>,
        Tycho Andersen <tycho@...ho.ws>,
        "Theodore Ts'o" <tytso@....edu>, Andi Kleen <ak@...ux.intel.com>,
        David Chinner <david@...morbit.com>,
        Nick Piggin <npiggin@...il.com>,
        Rik van Riel <riel@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jonathan Corbet <corbet@....net>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH v3 13/15] dcache: Provide a dentry constructor

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@...nel.org>
---
 fs/dcache.c | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index aac41adf4743..606cfca20d42 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 +1668,7 @@ 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 +3101,17 @@ 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