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SubjectRe: [PATCH] net: xfrm: use preempt-safe this_cpu_read() in ipcomp_alloc_tfms()
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On 03/07/2018 11:33 PM, Herbert Xu wrote:
> On Wed, Mar 07, 2018 at 11:24:16AM -0800, Greg Hackmann wrote:
>> f7c83bcbfaf5 ("net: xfrm: use __this_cpu_read per-cpu helper") added a
>> __this_cpu_read() call inside ipcomp_alloc_tfms(). Since this call was
>> introduced, the rules around per-cpu accessors have been tightened and
>> __this_cpu_read() cannot be used in a preemptible context.
>>
>> syzkaller reported this leading to the following kernel BUG while
>> fuzzing sendmsg:
>
> How about reverting f7c83bcbfaf5 instead?
>
> Thanks,
>

Because that would not be nice.

this_cpu_read() is faster than going through raw_smp_processor_id() and
per_cpu_ptr()

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