Daniel Axtens <dja@xxxxxxxxxx> writes:
> Lukas Bulwahn <lukas.bulwahn@xxxxxxxxx> writes:
>
>> Commit 66f24fa766e3 ("mm: drop redundant ARCH_ENABLE_SPLIT_PMD_PTLOCK")
>> selects the non-existing config ARCH_ENABLE_PMD_SPLIT_PTLOCK in
>> ./arch/powerpc/platforms/Kconfig.cputype, but clearly it intends to select
>> ARCH_ENABLE_SPLIT_PMD_PTLOCK here (notice the word swapping!), as this
>> commit does select that for all other architectures.
>>
>> Rectify selection to ARCH_ENABLE_SPLIT_PMD_PTLOCK instead.
>>
>
> Yikes, yes, 66f24fa766e3 does seem to have got that wrong. It looks like
> that went into 5.13.
>
> I think we want to specifically target this for stable so that we don't
> lose the perfomance and scalability benefits of split pmd ptlocks:
>
> Cc: stable@xxxxxxxxxxxxxxx # v5.13+
>
> (I don't think you need to do another revision for this, I think mpe
> could add it when merging.)
Yeah. I rewrote the change log a bit to make it clear this is a bug fix,
not a harmless cleanup.
cheers
powerpc: Re-enable ARCH_ENABLE_SPLIT_PMD_PTLOCK
Commit 66f24fa766e3 ("mm: drop redundant ARCH_ENABLE_SPLIT_PMD_PTLOCK")
broke PMD split page table lock for powerpc.
It selects the non-existent config ARCH_ENABLE_PMD_SPLIT_PTLOCK in
arch/powerpc/platforms/Kconfig.cputype, but clearly intended to
select ARCH_ENABLE_SPLIT_PMD_PTLOCK (notice the word swapping!), as
that commit did for all other architectures.
Fix it by selecting the correct symbol ARCH_ENABLE_SPLIT_PMD_PTLOCK.
Fixes: 66f24fa766e3 ("mm: drop redundant ARCH_ENABLE_SPLIT_PMD_PTLOCK")
Cc: stable@xxxxxxxxxxxxxxx # v5.13+
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@xxxxxxxxx>
Reviewed-by: Daniel Axtens <dja@xxxxxxxxxx>
[mpe: Reword change log to make it clear this is a bug fix]
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20210819113954.17515-3-lukas.bulwahn@xxxxxxxxx
