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Date: Thu, 5 May 2022 19:20:24 -0400
From: Joseph Salisbury <joseph.salisbury@...onical.com>
To: tglx@...utronix.de
Cc: linux-kernel@...r.kernel.org, dave.hansen@...ux.intel.com,
linux-rt-users@...r.kernel.org
Subject: Re: Issue With real-time patches on 5.15.y
On 5/5/22 19:18, Joseph Salisbury wrote:
> Hello,
>
> I ran into a build failure after applying the rt40 real-time
> patches[0] to an Ubuntu 22.04 kernel. The Ubuntu kernel is based on
> upstream stable 5.15.y(5.15.34 currently). I believe this patch is
> the specific one that introduces the build issue:
> 0086-locking-Allow-to-include-asm-spinlock_types.h-from-l.patch.
>
> After a bisect, the following commit was identified as the cause for
> the build failure:
> b50854eca0e0 ("x86/pkru: Remove useless include")
>
> This commit was added to mainline as of 5.16-rc1 and not Cc'd to
> stable, so it should not exist in 5.15.y. However, it was purposely
> added to the Ubuntu kernel to enable x86 AMX support[1].
>
> The real-time kernel build failure can be resolved by reverting commit
> b50854eca0e0. The failure seems to be due to the removal of an
> include of xstate.h from pkru.h and caused spinlock_t to not be
> defined. The commit would only be reverted for the real-time kernel
> and not any other kernels. I wanted to see if reverting the commit is
> the proper approach, or if cherry-picking additional commits might be
> a better solution in preparation for additional changes that might be
> coming in the future?
>
> Any suggestions would be greatly appreciated.
>
> Thanks,
>
> Joe
>
>
> [0]
> https://cdn.kernel.org/pub/linux/kernel/projects/rt/5.15/older/patches-5.15.34-rt40.tar.gz
> [1] https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1967750
Also, the following is the build failure that happens:
arch/x86/include/asm/pgtable.h:55:8: error: unknown type name 'spinlock_t'
55 | extern spinlock_t pgd_lock;
| ^~~~~~~~~~
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