linux-kernel - Re: [PATCH 6.12] Drivers: hv: Make the sysfs node size for the ring buffer dynamic

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Message-ID: <8f642ca2-04dc-4d87-b120-5d128ec3202e@t-8ch.de>
Date: Fri, 1 Aug 2025 12:52:15 +0200
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Naman Jain <namjain@...ux.microsoft.com>
Cc: Michael Kelley <mhklinux@...look.com>, 
	"stable@...r.kernel.org" <stable@...r.kernel.org>, Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>, 
	"K . Y . Srinivasan" <kys@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>, 
	Long Li <longli@...rosoft.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	"linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 6.12] Drivers: hv: Make the sysfs node size for the ring
 buffer dynamic

Hi Naman,

On 2025-07-31 21:13:27+0530, Naman Jain wrote:
> On 7/30/2025 1:15 AM, Michael Kelley wrote:
> > From: Thomas Weißschuh <linux@...ssschuh.net> Sent: Tuesday, July 29, 2025 11:47 AM
> > > On 2025-07-29 18:39:45+0000, Michael Kelley wrote:
> > > > From: Naman Jain <namjain@...ux.microsoft.com> Sent: Wednesday, July 23, 2025 12:02 AM
<snip>

> > > > Unfortunately, I don't see a fix, short of backporting support for the
> > > > .bin_size function, as this is exactly the problem that function solves.
> > > 
> > > It should work out in practice. (I introduced the .bin_size function)
> > 
> > The race I describe is unlikely, particularly if attribute groups are created
> > once and then not disturbed. But note that the Hyper-V fcopy group can
> > get updated in a running VM via update_sysfs_group(), which also calls
> > create_files(). Such an update might marginally increase the potential for
> > the race and for getting the wrong size. Still, I agree it should work out
> > in practice.
> > 
> > Michael
> > 
> > > 
> > > Thomas
> 
> hi Thomas,
> Would it be possible to port your changes on 6.12 kernel, to avoid such
> race conditions?

Possible, surely. But Greg has to accept it.
And you will need to do the backports.

> Or if it has a lot of dependencies, or if you have a
> follow-up advice, please let us us know.

Not more than mentioned before.


Thomas