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

[Vlastimil Babka]

On 1/5/26 22:40, Steven Rostedt wrote:
> On Mon, 05 Jan 2026 16:08:56 +0100
> Vlastimil Babka <vbabka@xxxxxxx> wrote:
> 
>> +++ b/mm/page_alloc.c
>> @@ -167,6 +167,31 @@ static inline void __pcp_trylock_noop(unsigned long *flags) { }
>>  	pcp_trylock_finish(UP_flags);					\
>>  })
>>  
>> +/*
>> + * With the UP spinlock implementation, when we spin_lock(&pcp->lock) (for i.e.
>> + * a potentially remote cpu drain) and get interrupted by an operation that
>> + * attempts pcp_spin_trylock(), we can't rely on the trylock failure due to UP
>> + * spinlock assumptions making the trylock a no-op. So we have to turn that
>> + * spin_lock() to a spin_lock_irqsave(). This works because on UP there are no
>> + * remote cpu's so we can only be locking the only existing local one.
>> + */
>> +#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:

----8<----