Re: [PATCH v2 1/2] kasan: support instrumented bitops combined with generic bitops

[Daniel Axtens <dja@axtens.net>]

> test_bit() is an atomic bitop. I assume it was meant to be in
> instrumented-atomic.h?

Hmm, interesting.

I was tricked by the generic version doing just a simple read, with only
a volatile attribute to ensure the read occurs more-or-less as written:

/**
 * test_bit - Determine whether a bit is set
 * @nr: bit number to test
 * @addr: Address to start counting from
 */
static inline int test_bit(int nr, const volatile unsigned long *addr)
{
        return 1UL & (addr[BIT_WORD(nr)] >> (nr & (BITS_PER_LONG-1)));
}

But the docs do seem to indicate that it's atomic (for whatever that
means for a single read operation?), so you are right, it should live in
instrumented-atomic.h.

Sadly, only x86 and s390 specify an arch_test_bit, which will make moving it
into instumented-atomic.h break powerpc :(

I'll have a crack at something next week, probably with a similar trick
to arch_clear_bit_unlock_is_negative_byte.

Regards,
Daniel


>
> Thanks,
> -- Marco
>
>> >> +
>> >> +#endif /* _ASM_GENERIC_BITOPS_INSTRUMENTED_NON_ATOMIC_H */
>> >> --
>> >> 2.20.1
>>
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