linux-kernel - [PATCH 3/7] proc: Mov rcu_read_(lock|unlock) in proc_prune_siblings

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Date:   Thu, 20 Feb 2020 14:49:09 -0600
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        LKML <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux API <linux-api@...r.kernel.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        Linux Security Module <linux-security-module@...r.kernel.org>,
        Akinobu Mita <akinobu.mita@...il.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Daniel Micay <danielmicay@...il.com>,
        Djalal Harouni <tixxdz@...il.com>,
        "Dmitry V . Levin" <ldv@...linux.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Jeff Layton <jlayton@...chiereds.net>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Solar Designer <solar@...nwall.com>
Subject: [PATCH 3/7] proc: Mov rcu_read_(lock|unlock) in proc_prune_siblings_dcache


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" <ebiederm@...ssion.com>
---
 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