linux-kernel - Re: [PATCH v2 2/5] rosebush: Add new data structure

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Date: Wed, 26 Jun 2024 14:07:58 +0100
From: Matthew Wilcox <willy@...radead.org>
To: linux-kernel@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org, maple-tree@...ts.infradead.org
Subject: Re: [PATCH v2 2/5] rosebush: Add new data structure

On Tue, Jun 25, 2024 at 10:17:57PM +0100, Matthew Wilcox (Oracle) wrote:
> Rosebush is a resizing hash table.  See
> Docuemntation/core-api/rosebush.rst for details.

I thought I had more debugging enabled than I actually did, and
there's some unbalanced RCU locking.  I'll fold this fix in:

diff --git a/lib/rosebush.c b/lib/rosebush.c
index 47106a04d11d..ab2d314cecec 100644
--- a/lib/rosebush.c
+++ b/lib/rosebush.c
@@ -305,13 +305,14 @@ static int rbh_split_bucket(struct rbh *rbh, struct rbh_bucket *bucket,
 	rcu_read_unlock();
 
 	/* XXX: use slab */
+	err = -ENOMEM;
 	buckets[0] = kmalloc(sizeof(*bucket), GFP_KERNEL);
 	if (!buckets[0])
-		return -ENOMEM;
+		goto nomem;
 	buckets[1] = kmalloc(sizeof(*bucket), GFP_KERNEL);
 	if (!buckets[1]) {
 		kfree(buckets[0]);
-		return -ENOMEM;
+		goto nomem;
 	}
 
 //printk("%s: adding buckets %p %p for hash %d\n", __func__, buckets[0], buckets[1], hash);
@@ -320,6 +321,8 @@ static int rbh_split_bucket(struct rbh *rbh, struct rbh_bucket *bucket,
 	table = (struct rbh_table *)(tagged & (tagged + 1));
 	mask = tagged - (unsigned long)table;
 	hash &= mask;
+
+	err = 0;
 	if (rbh_dereference_protected(table->buckets[hash], rbh) != bucket)
 		goto free;
 
@@ -354,14 +357,17 @@ static int rbh_split_bucket(struct rbh *rbh, struct rbh_bucket *bucket,
 	rbh_resize_unlock(rbh);
 	kvfree_rcu_mightsleep(bucket);
 
+	rcu_read_lock();
 	return 0;
 free:
 	rbh_resize_unlock(rbh);
 //printk("%s: freeing bucket %p\n", __func__, bucket);
-	kfree(buckets[0]);
 	kfree(buckets[1]);
+nomem:
+	kfree(buckets[0]);
 
-	return 0;
+	rcu_read_lock();
+	return err;
 }
 
 static int __rbh_insert(struct rbh *rbh, u32 hash, void *p)