Re: [PATCH] cxl: Convert pioson ops rwsem usages to scope based resource management

[Dan Williams <dan.j.williams@intel.com>]

Alison Schofield wrote:
> On Wed, Nov 15, 2023 at 04:55:11PM -0700, Dave Jiang wrote:
> > 
> > 
> > On 11/15/23 16:32, Alison Schofield wrote:
> > > On Tue, Nov 14, 2023 at 11:25:20AM -0700, Dave Jiang wrote:
> > >> Cleanup the rwsem usages in the poison ops to reduce complexity and reduce
> > >> code lines.
> > >>
> > >> Signed-off-by: Dave Jiang <dave.jiang@intel.com>
> > >> ---
> > >>
> > >> Hi Alison, follow on patch to yours. Can't be backported, but nice clean
> > >> up going forward.
> > > 
> > > Tell me more about your backport worry.  Are we expected to avoid using
> > > the new guard any place where there is a backport possibility?  
> > 
> > Given that there's none of the cleanup.h support in stable kernels, I don't see how we can backport the guard() code automatically. Thus your original fix with a fixes tag plus a new cleanup patch follow on w/o backport issues seems necessary. Otherwise a separate backport patch would be needed no?
> 
> Sure, it would be needed. I guess I'm looking for why this backport
> issue is so special. (not being sarcastic). Is there specific guidance
> not to use the cleanup stuff if we think a patch might be backported?
> I don't usually consider backportability when adding a Fixes tag to a
> Patch. Have 'backport folks' asked us not to use it?
> 
> I'm imagining the slippery slope of not fixing something the best way
> because we are worried that backport folks can't figure out how to
> merge it.

Upstream should be fixing things "the best way" in the current kernel.
If the best way requires some work when backporting, so be it.

The general rule for making backports easier is for when a fix
identifies additional cleanups. In that scenario the fix should be made
first and then the cleanups layered on top.

The cleanup.h helpers are an interesting case because they allow adding
new locking calls and defining the scope of the lock at the same time. I
submit that cleanup.h helpers are as easy / difficult to backport as
open-coded lock / unlock calls.