linux-kernel - Re: Large modules with 6.15 [was: [PATCH v4 6/6] percpu/x86: Enable strict percpu checks via named AS qualifiers]

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Message-ID: <b67d720104bf97cfeb5c34132f75edc9bf97cb3a.camel@HansenPartnership.com>
Date: Sat, 07 Jun 2025 10:31:05 -0400
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: Dave Hansen <dave.hansen@...el.com>, Uros Bizjak <ubizjak@...il.com>
Cc: Jiri Slaby <jirislaby@...nel.org>, x86@...nel.org, linux-mm@...ck.org, 
 linux-kernel@...r.kernel.org, linux-bcachefs@...r.kernel.org, 
 linux-arch@...r.kernel.org, netdev@...r.kernel.org, Nadav Amit
 <nadav.amit@...il.com>, Dennis Zhou <dennis@...nel.org>, Tejun Heo
 <tj@...nel.org>,  Christoph Lameter <cl@...ux.com>, Thomas Gleixner
 <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>, Borislav Petkov
 <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin"
 <hpa@...or.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Andy
 Lutomirski <luto@...nel.org>, Brian Gerst <brgerst@...il.com>, Peter
 Zijlstra <peterz@...radead.org>, Shung-Hsi Yu <shung-hsi.yu@...e.com>,
 Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: Large modules with 6.15 [was: [PATCH v4 6/6] percpu/x86: Enable
 strict percpu checks via named AS qualifiers]

On Sat, 2025-06-07 at 07:12 -0700, Dave Hansen wrote:
[...]
> James, by partial revert, did you mean to revert in stable but not
> mainline? I assumed you meant to just revert patch 6/6 of the series
> (stable and mainline) but leave 1-5 in place so turning it back on
> later was easier.

No, we had to put the revert through mainline because too many people
who build their own kernels use the firmware service.

We definitely didn't revert the entire series.  I constructed a new
patch which was effectively a partial revert only of the behaviour that
was tickling the bug.

For the record, this was the series containing the problem:

https://lore.kernel.org/all/20250119151214.23562-1-James.Bottomley@HansenPartnership.com/

And this is the revert we eventually came up with:

https://lore.kernel.org/all/63837c36eceaf8cf2af7933dccca54ff4dd9f30d.camel@HansenPartnership.com/

So it was specifically not a general revert but a narrowly crafted one
to get firmware services working again.

The mechanism we did was to queue the revert as an -rc fix so it went
in immediately and got backported to stable and then queue the revert
of the revert for the next merge window (and check before sending to
Linus that the user space update had spread far enough otherwise we'd
have skipped to the merge window after).

Regards,

James