Messages in this thread | | | Date | Tue, 1 Jan 2013 21:17:28 +0000 | From | Eric Wong <> | Subject | Re: [PATCH] poll: prevent missed events if _qproc is NULL |
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Eric Wong <normalperson@yhbt.net> wrote: > Eric Dumazet <eric.dumazet@gmail.com> wrote: > > commit 626cf236608505d376e4799adb4f7eb00a8594af should not have this > > side effect, at least for poll()/select() functions. The epoll() changes > > I am not yet very confident. > > I have a better explanation of the epoll problem below. > > An alternate version (limited to epoll) would be: > > diff --git a/fs/eventpoll.c b/fs/eventpoll.c > index cd96649..ca5f3d0 100644 > --- a/fs/eventpoll.c > +++ b/fs/eventpoll.c > @@ -1299,6 +1299,7 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi, struct epoll_even > * Get current event bits. We can safely use the file* here because > * its usage count has been increased by the caller of this function. > */ > + smp_mb(); > revents = epi->ffd.file->f_op->poll(epi->ffd.file, &pt); > > /* > > > I suspect a race already existed before this commit, it would be nice to > > track it properly. > > I don't believe this race existed before that change.
I was wrong, rereading 626cf236608505d376e4799adb4f7eb00a8594af, I think this race existed before.
Perhaps my alternate patch above is a better fix.
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