linux-kernel - Re: [PATCH] epoll

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Message-ID: <20130624170856.GA475@redhat.com>
Date:	Mon, 24 Jun 2013 19:08:56 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] epoll_wait: fix EINTR leak

On 06/24, Denys Vlasenko wrote:
>
> Usage of EINTR is wrong.

I agree, this is not nice. However "fix EINTR leak" doesn't look
accurate, -EINTR is fine as an error code. Just the syscall should
restart if possible.

> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -1598,7 +1598,7 @@ fetch_events:
>  			if (ep_events_available(ep) || timed_out)
>  				break;
>  			if (signal_pending(current)) {
> -				res = -EINTR;
> +				res = -ERESTARTNOHAND;

This and other similar changes do look right.

Say, sys_epoll_wait(). With this patch it can sleep, then return
ERESTARTNOHAND.

And we restart it with the same timeout again. If you want to
make it restartable, you need ERESTART_RESTARTBLOCK and
do_restart_epoll_wait() which we do not have.

See for example sys_poll() which implements this logic.

Oleg.

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