Re: [PATCH] epoll: prevent missed events on EPOLL_CTL_MOD

Eric Wong
2013-01-02T21:16:35Z

Eric Wong <normalperson@yhbt.net> wrote:
> Linus Torvalds <torvalds@linux-foundation.org> wrote:
> > Please document the barrier that this mb() pairs with, and then give
> > an explanation for the fix in the commit message, and I'll happily
> > take it. Even if it's just duplicating the comments above the
> > wq_has_sleeper() function, except modified for the ep_modify() case.
>
> Hopefully my explanation is correct and makes sense below,
> I think both effects of the barrier are needed

I noticed Linus accepted this already. This should probably go to
stable, right?

>From ancient git history[1], it seems this bug exists for all
2.6 kernels:

commit 424980a87e226d63af46579b2af16ec1b8d17e52
Author: Davide Libenzi <davidel@xmailserver.org>
Date: Thu Nov 14 16:17:23 2002 -0800

[PATCH] epoll bits 0.46 ...

[1] - git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git