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SubjectRe: Subtle MM bug

On Thu, Jan 11, 2001 at 11:50:21AM -0500, Albert D. Cahalan wrote:
> Stephen C. Tweedie writes:
> >
> > 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

We already have that...

> 2. threads are commanded to change their own copy

We already do that: that's how the current pthreads works.

> 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.

Yuck. Far better to send a signal than to pollute the syscall exit
path. And what about syscalls which block indefinitely? We _want_
the signal so that they get woken up to do the credentials change.


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