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SubjectRe: Stack traces in 2.6.9-rc2-mm4
Ingo Molnar wrote:
> * Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
>
>>>+ preempt_disable();
>>> /* if over the trickle threshold, use only 1 in 4096 samples */
>>> if ( random_state->entropy_count > trickle_thresh &&
>>> (__get_cpu_var(trickle_count)++ & 0xfff))
>>>- return;
>>>+ goto out;
>>>
>>
>>It looks like upstream code *is* buggy because that is a non-atomic
>>RMW operation on the per-cpu var, no? Hence you must disable preempt.
>
>
> no, the upstream code (i.e. BK-curr) is not buggy, because there this
> code runs under the BKL, implicitly as part of vt_ioctl() - and the BKL
> disables preemption in the upstream kernel.
>
> Yes, the code is fragile, but it's not buggy. With the remove-bkl patch
> this fragility turned into an outright bug. (Fortunately the patch
> detects all such incidents.)
>

Ahh yeah you're right, sorry.
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