Re: [PATCH v2 net] net: xfrm: use preempt-safe this_cpu_read() in ipcomp_alloc_tfms()

[Herbert Xu]

On Wed, Mar 07, 2018 at 02:42:53PM -0800, Greg Hackmann wrote:
> f7c83bcbfaf5 ("net: xfrm: use __this_cpu_read per-cpu helper") added a
> __this_cpu_read() call inside ipcomp_alloc_tfms().
> 
> At the time, __this_cpu_read() required the caller to either not care
> about races or to handle preemption/interrupt issues.  3.15 tightened
> the rules around some per-cpu operations, and now __this_cpu_read()
> should never be used in a preemptible context.  On 3.15 and later, we
> need to use this_cpu_read() instead.
> 
> syzkaller reported this leading to the following kernel BUG while
> fuzzing sendmsg:

Please explain why we can't revert f7c83bcbfaf5 instead.

Your patch contradicts the comment above the line that you're
changing.

Thanks,
-- 
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
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