Re: [PATCH] fix race in mark_mounts_for_expiry()

[David Howells <dhowells@redhat.com>]

Miklos Szeredi <miklos@szeredi.hu> wrote:

> Do you think my original fix is wrong, or is this just cosmetics?

What you're doing is tricky. It's asking for a race. Admittedly, it may not
occur in the particular situation you're looking at, but can you always
guarantee that? Remember, it may be a race against some piece of code that's
not yet written, by an author who doesn't realise what _you_ are doing here
because their changeset doesn't intersect with yours.

Remember: you have, in effect, made the usage count on that structure
non-atomic.

I do something like that in rwsems and it's something I have to be very
careful about. The main reason I can get away with it is that the actual
implementation of rwsems is small and is located in a very restrictes set of
places and it's not intermingled with other stuff.

David