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SubjectRe: [PATCH] fix race in mark_mounts_for_expiry()
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> And I think you're just adding to the case for removing mnt_namespace
> entirely. We'd still keep CLONE_NS, and users currently using
> namespaces (in the normal ways) would see no difference.
>
> mnt_namespace has these visible effects:
>
> - Prevents some tasks from mounting/umounting in a "foreign"
> namespace, even when they are granted access to the directory
> tree of the foreign namespace.
>
> It's not clear if the restriction is a useful security tool.
>
> - Causes every mount in a mount tree to be detached (independently),
> when last task associated with a namespace is destroyed.

I don't understand. The tree _has_ to be detached when no task uses
the namespace. That is the main purpose of the namespace structure,
to provide an anchor for the mount tree.

> And this invisible effect:
>
> - More concurrency than a global mount lock would have.

This is the key issue I think. It may even have security implications
in the future if we want to allow unprivileged mounts : a user could
DoS the system by just doing lots of mounts umounts in a private
namespace.

Miklos



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