Re: [PATCH] cgroup: fix cgroup_path() vs rename() race

Li Zefan
2013-01-26T00:21:30Z

On 2013/1/26 0:42, Tejun Heo wrote:
> On Fri, Jan 25, 2013 at 03:09:59PM +0800, Li Zefan wrote:
>> rename() will change dentry->d_name. The result of this race can
>> be worse than seeing partially rewritten name, but we might access
>> a stale pointer because rename() will re-allocate memory to hold
>> a longer name.
>>
>> Use dentry_path_raw(), and this vfs API will take care of lockings.
>>
>> Signed-off-by: Li Zefan <lizefan@huawei.com>
>
> Urgh... why do we even support rename? :(
>

Added in this commit many years ago:

commit 18a19cb3047e454ee5ecbc35d7acf3f8e09e0466
Author: Paul Jackson <pj@sgi.com>
Date: Sun Oct 30 15:02:31 2005 -0800

[PATCH] cpusets: simple rename

Add support for renaming cpusets. Only allow simple rename of cpuset
directories in place. Don't allow moving cpusets elsewhere in hierarchy or
renaming the special cpuset files in each cpuset directory.

The usefulness of this simple rename became apparent when developing task
migration facilities. It allows building a second cpuset hierarchy using
new names and containing new CPUs and Memory Nodes, moving tasks from the
old to the new cpusets, removing the old cpusets, and then renaming the new
cpusets to be just like the old names, so that any knowledge that the tasks
had of their cpuset names will still be valid.

Leaf node cpusets can be migrated to other CPUs or Memory Nodes by just
updating their 'cpus' and 'mems' files, but because no cpuset can contain
CPUs or Nodes not in its parent cpuset, one cannot do this in a cpuset
hierarchy without first expanding all the non-leaf cpusets to contain the
union of both the old and new CPUs and Nodes, which would obfuscate the
one-to-one migration of a task from one cpuset to another required to
correctly migrate the physical page frames currently allocated to that
task.

Signed-off-by: Paul Jackson <pj@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>