Re: [PATCH] riscv: Use an atomic xchg in pudp_huge_get_and_clear()

[Alexandre Ghiti]

On 9/20/25 03:39, Paul Walmsley wrote:
> Hi Alex,
>
> On Thu, 14 Aug 2025, Alexandre Ghiti wrote:
>
> > Make sure we return the right pud value and not a value that could
> > have been overwritten in between by a different core.
> >
> > Fixes: c3cc2a4a3a23 ("riscv: Add support for PUD THP")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> > ---
> > Note that this will conflict with
> > https://lore.kernel.org/linux-riscv/20250625063753.77511-1-ajd@xxxxxxxxxxxxx/
> > if applied after 6.17.
> Two quick questions on this one:
>
> - I see that you're using atomic_long_xchg() here and in some similar
> functions in pgtable.h, rather than xchg().  Was curious about the
> rationale for that?


Both functions amount to the same, I just used the same function as for 
existing similar functions.


> - x86 avoids the xchg() for !CONFIG_SMP.  Should we do the same?


Sounds like micro optimization to me, but up to you.


> thanks,
>
> - Paul