PATCH fs/proc: unregister_sysctl_table hanging

PATCH fs/proc: unregister_sysctl_table hanging

[Francesco Ruggeri]

unregister_sysctl_table hangs if all references to its
ctl_table_header structure are not dropped.
This happens sometimes because of a leak in proc_sys_lookup().
proc_sys_lookup() gets a reference to the table via lookup_entry(), but it
does not release it when a subsequent call to sysctl_follow_link() fails.
This patch fixes this leak by making sure the reference is always dropped
on return.
See also 076c3eed2c31773200b082568957fd8852ae93d7 which reorganized this
code in 3.4.

Tested in Linux 3.4.4.

Signed-off-by: Francesco Ruggeri <fruggeri@aristanetworks.com>

Index: linux-3.4.x86_64/fs/proc/proc_sysctl.c
===================================================================
--- linux-3.4.x86_64.orig/fs/proc/proc_sysctl.c
+++ linux-3.4.x86_64/fs/proc/proc_sysctl.c
@@ -462,9 +462,6 @@ static struct dentry *proc_sys_lookup(st

 	err = ERR_PTR(-ENOMEM);
 	inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p);
-	if (h)
-		sysctl_head_finish(h);
-
 	if (!inode)
 		goto out;

@@ -473,6 +470,8 @@ static struct dentry *proc_sys_lookup(st
 	d_add(dentry, inode);

 out:
+	if (h)
+		sysctl_head_finish(h);
 	sysctl_head_finish(head);
 	return err;
 }