Re: -next regression: "driver cohandle -EPROBE_DEFER from bus_type.match()"

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Thu, Dec 17, 2015 at 07:51:14AM -0800, Dan Williams wrote:
> The commit below causes the libnvdimm sub-system to stop loading.
> This is due to the fact that nvdimm_bus_match() returns the result of
> test_bit() which may be negative.  If there are any other bus match
> functions using test_bit they may be similarly impacted.
> 
> Can we queue a fixup like the following to libnvdimm, and maybe
> others, ahead of this driver core change?

This is rather annoying.  Have we uncovered a latent bug in other
architectures?  Well, looking through the test_bit() implementations,
it looks like it.

I'll drop the patch set for the time being, we can't go around breaking
stuff like this.  However, I think the test_bit() result should be
regularised across different architectures - it _looks_ to me like most
implementations return 0/1 values, but there may be some that don't
(maybe the assembly versions?)

Here's the list I've pulled out so far from the "easy" cases, which all
look like they're returning 0/1 values.

asm-generic: 0/1

/**
 * 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)));
}

alpha: 0/1

static inline int
test_bit(int nr, const volatile void * addr)
{
        return (1UL & (((const int *) addr)[nr >> 5] >> (nr & 31))) != 0UL;
}

arm: 0/1

test_bit(unsigned int nr, const volatile unsigned long *addr)
{
        unsigned long mask;

        addr += nr >> 5;

        mask = 1UL << (nr & 0x1f);

        return ((mask & *addr) != 0);
}

blackfin: 0/1

static inline int test_bit(int nr, const volatile unsigned long *addr)
{
        volatile const unsigned long *a = addr + (nr >> 5);
        return __raw_bit_test_asm(a, nr & 0x1f) != 0;
}

frv: 0/1

static inline int
__constant_test_bit(unsigned long nr, const volatile void *addr)
{
        return ((1UL << (nr & 31)) & (((const volatile unsigned int *) addr)[nr >> 5])) != 0;
}
(and similar for __test_bit)

h8300 uses assembly... no idea

hexagon uses assembly as well... no idea

ia64: 0/1

static __inline__ int
test_bit (int nr, const volatile void *addr)
{
        return 1 & (((const volatile __u32 *) addr)[nr >> 5] >> (nr & 31));
}

m68k: 0/1

static inline int test_bit(int nr, const unsigned long *vaddr)
{
        return (vaddr[nr >> 5] & (1UL << (nr & 31))) != 0;
}

mn10300: 0/1

static inline int test_bit(unsigned long nr, const volatile void *addr)
{
        return 1UL & (((const volatile unsigned int *) addr)[nr >> 5] >> (nr & 31));
}

s390: 0/1

static inline int test_bit(unsigned long nr, const volatile unsigned long *ptr)
{
        const volatile unsigned char *addr;

        addr = ((const volatile unsigned char *)ptr);
        addr += (nr ^ (BITS_PER_LONG - 8)) >> 3;
        return (*addr >> (nr & 7)) & 1;
}

x86: 0/1 for constant, ? for variable

static __always_inline int constant_test_bit(long nr, const volatile unsigned long *addr)
{
        return ((1UL << (nr & (BITS_PER_LONG-1))) &
                (addr[nr >> _BITOPS_LONG_SHIFT])) != 0;
}
(presumably variable_test_bit is the same, but I don't know)

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