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SubjectRe: [block IO crash] Re: 2.6.39-rc5-git2 boot crashs

* Pekka Enberg <penberg@kernel.org> wrote:

> Hi Tejun,
>
> On Wed, May 4, 2011 at 2:27 PM, Tejun Heo <tj@kernel.org> wrote:
> > Hmmm... if it's a race caused by preemtion enabled where it shouldn't
> > be, it's most likely the wrong type of this_cpu_cmpxchg_double() being
> > used in SLUB?  ie. __this_cpu_cmpxchg_double() where it should have
> > been this_cpu_cmpxchg_double()?  Christoph?
>
> There's no __this_cpu_cmpxchg_double() usage in mm/slub.c so I don't
> think it's that simple.

Well, AFAICS the problem is:

earth4:~/tip> grep cmpxchg mm/slub.c

if (unlikely(!this_cpu_cmpxchg_double(
if (unlikely(!this_cpu_cmpxchg_double(

Where this macro resolves to:

# define this_cpu_cmpxchg_double_8(pcp1, pcp2, oval1, oval2, nval1, nval2) \
_this_cpu_generic_cmpxchg_double(pcp1, pcp2, oval1, oval2, nval1, nval2)

where:

#define _this_cpu_generic_cmpxchg_double(pcp1, pcp2, oval1, oval2, nval1, nval2) \
({ \
int ret__; \
preempt_disable(); \
ret__ = __this_cpu_generic_cmpxchg_double(pcp1, pcp2, \
oval1, oval2, nval1, nval2); \
preempt_enable();
where:

#define __this_cpu_generic_cmpxchg_double(pcp1, pcp2, oval1, oval2, nval1, nval2) \
({ \
int __ret = 0; \
if (__this_cpu_read(pcp1) == (oval1) && \
__this_cpu_read(pcp2) == (oval2)) { \
__this_cpu_write(pcp1, (nval1)); \
__this_cpu_write(pcp2, (nval2)); \
__ret = 1; \
} \
(__ret); \
})

With is both IRQ and SMP unsafe.

Thanks,

Ingo
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