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

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Date:	Sat, 15 Dec 2007 21:58:52 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Alexey Kuznetsov <kuznet@....inr.ac.ru>
Cc:	Wang Chen <wangchen@...fujitsu.com>,
	Gerrit Renker <gerrit@....abdn.ac.uk>, davem@...emloft.net,
	andi@...stfloor.org, netdev@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Christoph Lameter <clameter@....com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH 3/3] [UDP6]: Counter increment on BH mode

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@...dor.apana.org.au>

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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--
diff --git a/include/net/snmp.h b/include/net/snmp.h
index ea206bf..9444b54 100644
--- a/include/net/snmp.h
+++ b/include/net/snmp.h
@@ -23,6 +23,7 @@
 
 #include <linux/cache.h>
 #include <linux/snmp.h>
+#include <linux/smp.h>
 
 /*
  * Mibs are stored in array of unsigned long.
@@ -137,7 +138,10 @@ struct linux_mib {
 #define SNMP_INC_STATS_OFFSET_BH(mib, field, offset)	\
 	(per_cpu_ptr(mib[0], raw_smp_processor_id())->mibs[field + (offset)]++)
 #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]++)
 #define SNMP_DEC_STATS(mib, field) 	\
@@ -145,6 +149,9 @@ struct linux_mib {
 #define SNMP_ADD_STATS_BH(mib, field, addend) 	\
 	(per_cpu_ptr(mib[0], raw_smp_processor_id())->mibs[field] += addend)
 #define SNMP_ADD_STATS_USER(mib, field, addend) 	\
-	(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)
 
 #endif
--
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