Re: [PATCH 3/3] [UDP6]: Counter increment on BH mode

[Eric Dumazet]

Herbert Xu a écrit :
> 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.
>
> This patch makes it use get_cpu/put_cpu to disable preemption.
>
> Signed-off-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
>
> Cheers,
 #define SNMP_INC_STATS_USER(mib, field) \
-	(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)
 #define SNMP_INC_STATS(mib, field) 	\
 	(per_cpu_ptr(mib[!in_softirq()], raw_smp_processor_id())->mibs[field]++)


How come you change SNMP_INC_STATS_USER() but not SNMP_INC_STATS() ?


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