Re: [PATCH v6 27/39] kasan, mm: only define ___GFP_SKIP_KASAN_POISON with HW_TAGS

[Vlastimil Babka <vbabka@suse.cz>]

On 3/23/22 14:02, Sebastian Andrzej Siewior wrote:
> On 2022-03-23 12:48:29 [+0100], Vlastimil Babka wrote:
>>> +#ifdef CONFIG_KASAN_HW_TAGS
>>>  #define ___GFP_SKIP_KASAN_POISON	0x1000000u
>>> +#else
>>> +#define ___GFP_SKIP_KASAN_POISON	0
>>> +#endif
>>>  #ifdef CONFIG_LOCKDEP
>>>  #define ___GFP_NOLOCKDEP	0x2000000u
>>>  #else
>>> @@ -251,7 +255,9 @@ struct vm_area_struct;
>>>  #define __GFP_NOLOCKDEP ((__force gfp_t)___GFP_NOLOCKDEP)
>>>  
>>>  /* Room for N __GFP_FOO bits */
>>> -#define __GFP_BITS_SHIFT (25 + IS_ENABLED(CONFIG_LOCKDEP))
>>> +#define __GFP_BITS_SHIFT (24 +					\
>>> +			  IS_ENABLED(CONFIG_KASAN_HW_TAGS) +	\
>>> +			  IS_ENABLED(CONFIG_LOCKDEP))
>>
>> This breaks __GFP_NOLOCKDEP, see:
>> https://lore.kernel.org/all/YjoJ4CzB3yfWSV1F@linutronix.de/
> 
> This could work because ___GFP_NOLOCKDEP is still 0x2000000u. In

Hm but already this patch makes gfp_allowed_mask to be 0x1ffffff (thus
not covering 0x2000000u) when CONFIG_LOCKDEP is enabled and the KASAN
stuff not? 0x8000000u is just even further away.

> 	("kasan, page_alloc: allow skipping memory init for HW_TAGS")
> 	https://lore.kernel.org/all/0d53efeff345de7d708e0baa0d8829167772521e.1643047180.git.andreyknvl@google.com/
> 
> This is replaced with 0x8000000u which breaks lockdep.
> 
> Sebastian
>