linux-kernel - [PATCH v2 3/6] proc: In proc_prune_siblings

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Message-ID: <87k14c0x2y.fsf_-_@x220.int.ebiederm.org>
Date:   Mon, 24 Feb 2020 10:27:49 -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>,
        Alexey Gladkov <gladkov.alexey@...il.com>
Subject: [PATCH v2 3/6] proc: In proc_prune_siblings_dcache cache an aquired super block


Because there are likely to be several sysctls in a row on the
same superblock cache the super_block after the count has
been raised and don't deactivate it until we are processing
another super_block.

Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 fs/proc/inode.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 74ce4a8d05eb..fa2dc732cd77 100644
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -108,10 +108,11 @@ void proc_prune_siblings_dcache(struct hlist_head *inodes, spinlock_t *lock)
 	struct inode *inode;
 	struct proc_inode *ei;
 	struct hlist_node *node;
-	struct super_block *sb;
+	struct super_block *old_sb = NULL;
 
 	rcu_read_lock();
 	for (;;) {
+		struct super_block *sb;
 		node = hlist_first_rcu(inodes);
 		if (!node)
 			break;
@@ -122,23 +123,28 @@ 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 ((sb != old_sb) && !atomic_inc_not_zero(&sb->s_active))
 			continue;
 		inode = igrab(inode);
 		rcu_read_unlock();
+		if (sb != old_sb) {
+			if (old_sb)
+				deactivate_super(old_sb);
+			old_sb = sb;
+		}
 		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();
+	if (old_sb)
+		deactivate_super(old_sb);
 }
 
 static int proc_show_options(struct seq_file *seq, struct dentry *root)
-- 
2.25.0