Re: [PATCH stable 6.1] devlink: Fix RCU stall when unregistering a devlink instance

[Ido Schimmel <idosch@nvidia.com>]

On Tue, Oct 01, 2024 at 02:11:27PM +0200, Greg KH wrote:
> On Tue, Oct 01, 2024 at 02:20:35PM +0300, Ido Schimmel wrote:
> > I read the stable rules and I am not providing an "upstream commit ID"
> > since the code in upstream has been reworked, making this fix
> > irrelevant. The only affected stable kernel is 6.1.y.
> 
> You need to document the heck out of why this is only relevant for this
> one specific kernel branch IN the changelog text, so that we understand
> what is going on, AND you need to get acks from the relevant maintainers
> of this area of the kernel to accept something that is not in Linus's
> tree.
> 
> But first of, why?  Why not just take the upstrema commits instead?

There were a lot of changes as part of the 6.3 cycle to completely
rework the semantics of the devlink instance reference count. As part of
these changes, commit d77278196441 ("devlink: bump the instance index
directly when iterating") inadvertently fixed the bug mentioned in this
patch. This commit cannot be applied to 6.1.y as-is because a prior
commit (also in 6.3) moved the code to a different file (leftover.c ->
core.c). There might be more dependencies that I'm currently unaware of.

The alternative, proposed in this patch, is to provide a minimal and
contained fix for the bug introduced in upstream commit c2368b19807a
("net: devlink: introduce "unregistering" mark and use it during
devlinks iteration") as part of the 6.0 cycle.

The above explains why the patch is only relevant to 6.1.y.

Jakub / Jiri, what is your preference here? This patch or cherry picking
a lot of code from 6.3?