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

Sebastian Andrzej Siewior
2022-03-23T13:03:56Z

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
("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