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From:   "Tobin C. Harding" <tobin@kernel.org>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     "Tobin C. Harding" <tobin@kernel.org>,
        Roman Gushchin <guro@fb.com>,
        Alexander Viro <viro@ftp.linux.org.uk>,
        Christoph Hellwig <hch@infradead.org>,
        Pekka Enberg <penberg@cs.helsinki.fi>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Christopher Lameter <cl@linux.com>,
        Matthew Wilcox <willy@infradead.org>,
        Miklos Szeredi <mszeredi@redhat.com>,
        Andreas Dilger <adilger@dilger.ca>,
        Waiman Long <longman@redhat.com>,
        Tycho Andersen <tycho@tycho.ws>,
        "Theodore Ts'o" <tytso@mit.edu>, Andi Kleen <ak@linux.intel.com>,
        David Chinner <david@fromorbit.com>,
        Nick Piggin <npiggin@gmail.com>,
        Rik van Riel <riel@redhat.com>,
        Hugh Dickins <hughd@google.com>,
        Jonathan Corbet <corbet@lwn.net>, linux-mm@kvack.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [RFC PATCH v3 13/15] dcache: Provide a dentry constructor
Date:   Thu, 11 Apr 2019 11:34:39 +1000
Message-Id: <20190411013441.5415-14-tobin@kernel.org>
In-Reply-To: <20190411013441.5415-1-tobin@kernel.org>
References: <20190411013441.5415-1-tobin@kernel.org>
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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 | 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