linux-kernel - Re: [RFC PATCH] epoll: Add synchronous wakeup support for ep_poll

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Message-ID: <2024121705-unrigged-sanitary-7b19@gregkh>
Date: Tue, 17 Dec 2024 16:34:08 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Brian Geffon <bgeffon@...gle.com>
Cc: "# v4 . 10+" <stable@...r.kernel.org>,
	Xuewen Yan <xuewen.yan@...soc.com>,
	Christian Brauner <brauner@...nel.org>, jack@...e.cz,
	dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
	mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
	cmllamas@...gle.com, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, ke.wang@...soc.com,
	jing.xia@...soc.com, xuewen.yan94@...il.com,
	viro@...iv.linux.org.uk, mingo@...hat.com, peterz@...radead.org,
	juri.lelli@...hat.com, vincent.guittot@...aro.org, lizeb@...gle.com
Subject: Re: [RFC PATCH] epoll: Add synchronous wakeup support for
 ep_poll_callback

On Tue, Dec 17, 2024 at 09:30:51AM -0500, Brian Geffon wrote:
> On Thu, Dec 12, 2024 at 12:14 PM Brian Geffon <bgeffon@...gle.com> wrote:
> >
> > On Wed, Oct 16, 2024 at 03:05:38PM -0400, Brian Geffon wrote:
> > > On Wed, Oct 16, 2024 at 03:10:34PM +0200, Christian Brauner wrote:
> > > > On Fri, 26 Apr 2024 16:05:48 +0800, Xuewen Yan wrote:
> > > > > Now, the epoll only use wake_up() interface to wake up task.
> > > > > However, sometimes, there are epoll users which want to use
> > > > > the synchronous wakeup flag to hint the scheduler, such as
> > > > > Android binder driver.
> > > > > So add a wake_up_sync() define, and use the wake_up_sync()
> > > > > when the sync is true in ep_poll_callback().
> > > > >
> > > > > [...]
> > > >
> > > > Applied to the vfs.misc branch of the vfs/vfs.git tree.
> > > > Patches in the vfs.misc branch should appear in linux-next soon.
> > > >
> > > > Please report any outstanding bugs that were missed during review in a
> > > > new review to the original patch series allowing us to drop it.
> > > >
> > > > It's encouraged to provide Acked-bys and Reviewed-bys even though the
> > > > patch has now been applied. If possible patch trailers will be updated.
> > > >
> > > > Note that commit hashes shown below are subject to change due to rebase,
> > > > trailer updates or similar. If in doubt, please check the listed branch.
> > > >
> > > > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
> > > > branch: vfs.misc
> > >
> > > This is a bug that's been present for all of time, so I think we should:
> > >
> > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > > Cc: stable@...r.kernel.org
> >
> > This is in as 900bbaae ("epoll: Add synchronous wakeup support for
> > ep_poll_callback"). How do maintainers feel about:
> >
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Cc: stable@...r.kernel.org
> 
> Dear stable maintainers, this fixes a bug goes all the way back and
> beyond Linux 2.6.12-rc2. Can you please add this commit to the stable
> releases?
> 
> commit 900bbaae67e980945dec74d36f8afe0de7556d5a upstream.

How is this a bugfix?  It looks like it is just a new feature being
added to epoll, what bug does it "fix"?

confused,

greg k-h