linux-kernel - Re: [RFC][PATCH] epoll: allow EPOLLWAKEUP flag if PM

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Message-ID: <12494461.XagJySeqkW@vostro.rjw.lan>
Date:	Wed, 13 Nov 2013 00:46:15 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Amit Pundir <amit.pundir@...aro.org>,
	Arve Hjønnevåg <arve@...roid.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>,
	Android Kernel Team <kernel-team@...roid.com>
Subject: Re: [RFC][PATCH] epoll: allow EPOLLWAKEUP flag if PM_SLEEP is enabled

On Tuesday, November 12, 2013 11:24:05 AM John Stultz wrote:
> On Mon, Nov 11, 2013 at 1:22 PM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> > On Monday, November 11, 2013 11:26:31 PM Amit Pundir wrote:
> >> While looking into the problem, I found that ep_create_wakeup_source()
> >> reports ENOMEM if wakeup_source_register() returns NULL.
> >> ep_create_wakeup_source() assumes that NULL is only returned if we run
> >> into ENOMEM but NULL is also returned when CONFIG_PM_SLEEP is disabled.
> >
> > So the error value should not be ENOMEM.
> 
> Right, ENOMEM is clearly wrong. I think its just not clear what the
> right thing to do is.
> 
> 
> >> If CONFIG_PM_SLEEP is disabled, stripping the EPOLLWAKEUP flag seems to
> >> be a reasonable solution here, allowing the call to succeed, while
> >> dropping the wakeup logic.  While returning EINVAL might also be a good
> >> solution, stripping the flag seems to follow the established behavior,
> >> as is done when the process doesn't have sufficient capabilities to
> >> block suspend.
> >
> > Which is a different thing.
> 
> Well, in the case of the process not having sufficient capabilities,
> -EPERM seems like a reasonable return value.  But instead the wakeup
> flag is silently dropped.  That's why Amit is asking if dropping the
> wakeup flag is also the right approach for the !PM_SLEEP case instead
> of returning EINVAL.
> 
> Dropping the wakeup flag is the easier solution, since we don't have
> to then go through all the userspace code and have it handle the error
> and resubmit without the wakeup flag.  I suspect this was the same
> consideration for the decision in the insufficient capabilities case,
> but I don't really know.

Yes, it was.

Thanks!

-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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