Re: [PATCH] Fix a race in pid generation that causes pids to be reused immediately.

tytso
2010-06-09T17:10:25Z

On Wed, Jun 09, 2010 at 09:06:37AM -0700, Linus Torvalds wrote:
>
> That seems to be purely an artifact of the cleverness of avoiding re-doing
> the whole loop, no? If we _had_ re-done the whole loop (the "normal"
> cmpxchg model), we would have re-started the whole pid search and handled
> the overflow in the existing overflow handling code.

This brings up a question. If we're going to use a cmpxchg() loop, is
there any point to doing the test-and-set game with the bitmap? It
should be just as fast to just use cmpxchg as it is to do the
test-and-set, and isn't it more likely that various CPU architectures
will have the cmpxchg than test-and-set-bit?

We might be able to radically simplify alloc_pidmap(). Would that
cause a huge problem on some non-Intel architectures, though?

- Ted