Re: [PATCH] Alternate futex non-page-pinning and COW fix

[Jamie Lokier]

Rusty Russell wrote:
> I don't have a problem with the omission.  mremap is logically
> equivalent to munmap + mmap, so it's a subset of the "I unmapped
> underneath my futex!".  It's not like it's going to happen without the
> caller knowing: if the address doesn't change, then the futexes won't
> break.  If they do, the caller needs to reset them anyway.

I think mremap() on block of memory containing futexes is reasonable.
Imagine a big data structure with a table futex locks at the start of
it.  I'm not sure how useful it is, but it's not worthless.

Anyway, I have a patch, tested, which moves remapped futexes _and_
returns EFAULT to waiters when pages are unmapped.  It's kept separate
from the main futex patch so you can accept it or not.

-- Jamie

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