linux-kernel - Re: -next regression: "driver cohandle -EPROBE_DEFER from bus

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Date:	Fri, 18 Dec 2015 13:18:36 +0900
From:	Yoshinori Sato <ysato@...rs.sourceforge.jp>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	tomeu.vizoso@...labora.com, m.szyprowski@...sung.com,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-nvdimm@...ts.01.org" <linux-nvdimm@...1.01.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: -next regression: "driver cohandle -EPROBE_DEFER from bus_type.match()"

On Fri, 18 Dec 2015 03:46:41 +0900,
Russell King - ARM Linux wrote:
> 
> 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
0/1
I think same return of other architecture.

> 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)
> 
> -- 
> FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
> according to speedtest.net.
> --
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-- 
Yoshinori Sato
<ysato@...rs.sourceforge.jp>
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