Re: [PATCH mm-hotfixes] mm/page_alloc: prevent pcp corruption with SMP=n

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 6 Jan 2026 09:28:29 +0100
Vlastimil Babka <vbabka@suse.cz> wrote:

> >> + */
> >> +#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
> >> +static inline void __flags_noop(unsigned long *flags) { }
> >> +#define spin_lock_maybe_irqsave(lock, flags)		\
> >> +({							\
> >> +	 __flags_noop(&(flags));			\
> >> +	 spin_lock(lock);				\
> >> +})
> >> +#define spin_unlock_maybe_irqrestore(lock, flags)	\
> >> +({							\
> >> +	 spin_unlock(lock);				\
> >> +	 __flags_noop(&(flags));			\
> >> +})
> >> +#else
> >> +#define spin_lock_maybe_irqsave(lock, flags)		spin_lock_irqsave(lock, flags)
> >> +#define spin_unlock_maybe_irqrestore(lock, flags)	spin_unlock_irqrestore(lock, flags)
> >> +#endif
> >> +  
> > 
> > These are very generic looking names for something specific for
> > page_alloc.c. Could you add a prefix of some kind to make it easy to see
> > that these are specific to the mm code?
> > 
> >  mm_spin_lock_maybe_irqsave() ?  
> OK, I think it's best like this:

Yeah, thanks.

-- Steve

> 
> ----8<----
> >From a6da5d9e3db005a2f44f3196814d7253dce21d3e Mon Sep 17 00:00:00 2001  
> From: Vlastimil Babka <vbabka@suse.cz>
> Date: Tue, 6 Jan 2026 09:23:37 +0100
> Subject: [PATCH] mm/page_alloc: prevent pcp corruption with SMP=n - fix
> 
> Add pcp_ prefix to the spin_lock_irqsave wrappers, per Steven.
> With that make them also take pcp pointer and reference the lock
> field themselves, to be like the existing pcp trylock wrappers.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>  mm/page_alloc.c | 30 ++++++++++++++++--------------
>  1 file changed, 16 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index ec3551d56cde..dd72ff39da8c 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -177,19 +177,21 @@ static inline void __pcp_trylock_noop(unsigned long *flags) { }
>   */
>  #if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
>  static inline void __flags_noop(unsigned long *flags) { }
> -#define spin_lock_maybe_irqsave(lock, flags)		\
> +#define pcp_spin_lock_maybe_irqsave(ptr, flags)		\
>  ({							\
>  	 __flags_noop(&(flags));			\
> -	 spin_lock(lock);				\
> +	 spin_lock(&(ptr)->lock);			\
>  })