# \[PATCH 3/7\] proc: Mov rcu\_read\_(lock\|unlock) in proc\_prune\_siblings\_dcache

- Subsystems: FILESYSTEMS (VFS and infrastructure), PROC FILESYSTEM, THE REST
- Maintainers: Alexander Viro, Christian Brauner, Linus Torvalds
- List: linux-api
- 2 messages, 2 authors
- Page: https://ratatoskr.run/linux-api/2020/02/173441/t

## \[PATCH 3/7\] proc: Mov rcu\_read\_(lock\|unlock) in proc\_prune\_siblings\_dcache

- From: Eric W. Biederman \<hidden\>
- Date: 2020-02-20 20:51:27 
- Message: https://ratatoskr.run/linux-api/2020/02/173441.md

```text

Don't make it look like rcu_read_lock is held over the entire loop
instead just take the rcu_read_lock over the part of the loop that
matters.  This makes the intent of the code a little clearer.

Signed-off-by: "Eric W. Biederman" <redacted>
---
 fs/proc/inode.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 74ce4a8d05eb..38a7baa41aba 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -110,11 +110,13 @@ void proc_prune_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock)
 	struct hlist_node *node;
 	struct super_block *sb;
 
-	rcu_read_lock();
 	for (;;) {
+		rcu_read_lock();
 		node = hlist_first_rcu(inodes);
-		if (!node)
+		if (!node) {
+			rcu_read_unlock();
 			break;
+		}
 		ei = hlist_entry(node, struct proc_inode, sibling_inodes);
 		spin_lock(lock);
 		hlist_del_init_rcu(&ei->sibling_inodes);
@@ -122,23 +124,21 @@ void proc_prune_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock)
 
 		inode = &ei->vfs_inode;
 		sb = inode->i_sb;
-		if (!atomic_inc_not_zero(&sb->s_active))
+		if (!atomic_inc_not_zero(&sb->s_active)) {
+			rcu_read_unlock();
 			continue;
+		}
 		inode = igrab(inode);
 		rcu_read_unlock();
 		if (unlikely(!inode)) {
 			deactivate_super(sb);
-			rcu_read_lock();
 			continue;
 		}
 
 		d_prune_aliases(inode);
 		iput(inode);
 		deactivate_super(sb);
-
-		rcu_read_lock();
 	}
-	rcu_read_unlock();
 }
 
 static int proc_show_options(struct seq_file *seq, struct dentry *root)
-- 
2.20.1

```

## Re: \[PATCH 3/7\] proc: Mov rcu\_read\_(lock\|unlock) in proc\_prune\_siblings\_dcache

- From: Linus Torvalds \<torvalds@linux-foundation.org\>
- Date: 2020-02-20 22:33:34 
- Message: https://ratatoskr.run/linux-api/2020/02/173451.md

```text
On Thu, Feb 20, 2020 at 12:51 PM Eric W. Biederman
[ref] wrote:
>
> Don't make it look like rcu_read_lock is held over the entire loop
> instead just take the rcu_read_lock over the part of the loop that
> matters.  This makes the intent of the code a little clearer.

No, this is horrid.

Maybe it makes the intent clearer, but it also causes that "continue"
case to unlock and relock immediately.

And maybe that case never triggers, and that's ok. But then it needs a
big comment about it.

              Linus
```