netdev - Re: Broken link in /sys/class/net/ [was: [GIT] Networking]

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Date:	Sat, 29 Oct 2011 21:49:47 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	Greg KH <gregkh@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Miller <davem@...emloft.net>,
	Mikulas Patocka <mpatocka@...hat.com>,
	akpm@...ux-foundation.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jiri Slaby <jirislaby@...il.com>
Subject: Re: Broken link in /sys/class/net/ [was: [GIT] Networking]

Jiri Slaby <jslaby@...e.cz> writes:

> On 10/25/2011 03:13 PM, Greg KH wrote:
>> On Tue, Oct 25, 2011 at 01:46:11PM +0200, Linus Torvalds wrote:
>>> Anyway, after that rant about really bad practices, let me say that I
>>> did fix up the conflict and I think it's right. But I won't guarantee
>>> it, so please check the changes to fs/sysfs/dir.c.
>> 
>> I think it looks ok, I've booted the merge result, and am typing and
>> sending this from the new kernel, and it hasn't crashed yet :)
>
> Hi, maybe this was not caused by the merge, but the patch[1] causes this
> mess in /sys/class/net/ for me:
> l????????? ? ?    ?    ?             ? eth1
>
> This happens after one renames a net device -- the new name is eth1 here.
>
> [1] 4f72c0cab40 (sysfs: use rb-tree for name lookups)

This looks pretty fixable but today sysfs_rename does not do anything
with the to move a renamed entry to a different position in the rbtree.

If the directory itself changes sysfs_rename should be fine, and it
looks like a trivial patch to always apply the directory rename logic
in sysfs_rename. 

I think all we need is something like the untested patch below to fix
the network device rename problem.

Eric

diff --git a/fs/sysfs/dir.c b/fs/sysfs/dir.c
index 48ffbdf..a294068 100644
--- a/fs/sysfs/dir.c
+++ b/fs/sysfs/dir.c
@@ -865,14 +865,13 @@ int sysfs_rename(struct sysfs_dirent *sd,
 		sd->s_name = new_name;
 	}
 
-	/* Remove from old parent's list and insert into new parent's list. */
-	if (sd->s_parent != new_parent_sd) {
-		sysfs_unlink_sibling(sd);
-		sysfs_get(new_parent_sd);
-		sysfs_put(sd->s_parent);
-		sd->s_parent = new_parent_sd;
-		sysfs_link_sibling(sd);
-	}
+	/* Move to the appropriate place in the appropriate directories rbtree. */
+	sysfs_unlink_sibling(sd);
+	sysfs_get(new_parent_sd);
+	sysfs_put(sd->s_parent);
+	sd->s_parent = new_parent_sd;
+	sysfs_link_sibling(sd);
+
 	sd->s_ns = new_ns;
 
 	error = 0;

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