* Herbert Xu <[email protected]> wrote:
> Ob Tue, Dec 04, 2007 at 12:17:23AM +1100, Herbert Xu wrote:
> >
> > Never mind, we already have that in local_t and as Alexey correctly
> > points out, USER is still going to be the expensive variant with the
> > preempt_disable (well until BH gets threaded). So how about this patch?
>
> I didn't hear any objections so here is the patch again.
>
> [SNMP]: Fix SNMP counters with PREEMPT
>
> The SNMP macros use raw_smp_processor_id() in process context which is
> illegal because the process may be preempted and then migrated to
> another CPU.
nit: please use 'invalid' instead of 'illegal'.
> This patch makes it use get_cpu/put_cpu to disable preemption.
>
> Signed-off-by: Herbert Xu <[email protected]>
> - (per_cpu_ptr(mib[1], raw_smp_processor_id())->mibs[field]++)
> + do { \
> + per_cpu_ptr(mib[1], get_cpu())->mibs[field]++; \
> + put_cpu(); \
> + } while (0)
> - (per_cpu_ptr(mib[1], raw_smp_processor_id())->mibs[field] += addend)
> + do { \
> + per_cpu_ptr(mib[1], get_cpu())->mibs[field] += addend; \
> + put_cpu(); \
> + } while (0)
we could perhaps introduce stat_smp_processor_id(), which signals that
the CPU id is used for statistical purposes and does not have to be
exact? In any case, your patch looks good too.
Ingo
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