Re: Subtle MM bug

From: Albert D. Cahalan (acahalan@cs.uml.edu)
Date: Thu Jan 11 2001 - 11:50:21 EST


Stephen C. Tweedie writes:
> On Wed, Jan 10, 2001 at 12:11:16PM -0800, Linus Torvalds wrote:

>> That said, we can easily support the notion of CLONE_CRED if
>> we absolutely have to (and sane people just shouldn't use it),
>> so if somebody wants to work on this for 2.5.x...
>
> But is it really worth the pain? I'd hate to have to audit the
> entire VFS to make sure that it works if another thread changes our
> credentials in the middle of a syscall, so we either end up having to
> lock the credentials over every VFS syscall, or take a copy of the
> credentials and pass it through every VFS internal call that we make.

1. each thread has a copy, and doesn't need to lock it
2. threads are commanded to change their own copy

Credentials could be changed on syscall exit. It is a bit like
doing signals I think, with less overhead than making userspace
muck around with signal handlers and synchronization crud.

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