linux-kernel - Re: [PATCH] sysfs: move assignment to be under lock in sysfs_remove

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Message-ID: <20131030223832.GA29216@kroah.com>
Date:	Wed, 30 Oct 2013 15:38:32 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Tejun Heo <tj@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sysfs: move assignment to be under lock in
 sysfs_remove_dir()

On Wed, Oct 30, 2013 at 02:41:16PM -0700, Eric W. Biederman wrote:
> One of the particularly problematic things that can happen with sysfs is
> that we can get a hotplug event in userspace and then examine sysfs and
> not find the attributes of the device because the kernel has not added
> them yet.
> 
> Which is a particularly good reason to have a campaign against
> independent usage of device_create_file and device_remove_file in the
> device users.

I have been working on that over the past few months, there are now
default attribute groups for all things, and those are used to create
the files _before_ the hotplug event goes to userspace.  I still have
more work to do to clean this up, but my goal is to remove
device_create_file() entirely, although we still have some work to go
for the platform driver case, which will take some time.

But we will get there eventually, it's a problem that has to be fixed as
more and more people hit this with multi-core, fast systems these days.

> At which point really the right thing to do when we delete a directory
> is to WARN and be very grumpy if there are any attributes in the
> directory we were removing.

We tried this once, and it was a mess.  But that was a long time ago,
maybe it's better now, I'll look and see...

thanks,

greg k-h
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