[Devel] Re: [Q] missing unused dentry in prune_dcache()?

[Vasily Averin]

David Howells wrote:
> Vasily Averin <vvs at sw.ru> wrote:
> 
>> I've noticed one more minor issue in your patch: in
>> shrink_dcache_for_umount_subtree() function you decrement
>> dentry_stat.nr_dentry without dcache_lock.
> 
> How about the attached patch?
I'm sorry, but your patch is wrong:
you have mixed calculation of 2 variables:
dentry_stat.nr_unused -- were correct, it was decremented under dcache_lock.
dentry_stat.nr_dentry -- were incorrect, it was decremented without dcache_lock.

You should correct dentry_stat.nr_dentry, but instead you broke calculation of
dentry_stat.nr_unused.

I've fixed this issue by following patch.

Thank you,
	Vasily Averin
---
VFS: Fix an error in dentry_stat.nr_dentry counting

From: Vasily Averin <vvs at sw.ru>

Fix an error in dentry_stat.nr_dentry counting in
shrink_dcache_for_umount_subtree() in which the count is modified without the
dcache_lock held.

Signed-Off-By: Vasily Averin <vvs at sw.ru>

--- linux-2.6.19-rc3/fs/dcache.c.nrdntr	2006-10-26 15:14:51.000000000 +0400
+++ linux-2.6.19-rc3/fs/dcache.c	2006-10-27 10:24:07.000000000 +0400
@@ -554,6 +554,7 @@ repeat:
 static void shrink_dcache_for_umount_subtree(struct dentry *dentry)
 {
 	struct dentry *parent;
+	unsigned detached = 0;

 	BUG_ON(!IS_ROOT(dentry));

@@ -618,7 +619,7 @@ static void shrink_dcache_for_umount_sub
 				atomic_dec(&parent->d_count);

 			list_del(&dentry->d_u.d_child);
-			dentry_stat.nr_dentry--;	/* For d_free, below */
+			detached++;

 			inode = dentry->d_inode;
 			if (inode) {
@@ -635,8 +636,8 @@ static void shrink_dcache_for_umount_sub
 			/* finished when we fall off the top of the tree,
 			 * otherwise we ascend to the parent and move to the
 			 * next sibling if there is one */
-			if (!parent)
-				return;
+			if (!parent)
+				goto out;

 			dentry = parent;

@@ -645,6 +646,11 @@ static void shrink_dcache_for_umount_sub
 		dentry = list_entry(dentry->d_subdirs.next,
 				    struct dentry, d_u.d_child);
 	}
+out:
+	/* several dentries were freed, need to correct nr_dentry */
+	spin_lock(&dcache_lock);
+	dentry_stat.nr_dentry -= detached;
+	spin_unlock(&dcache_lock);
 }

 /*