From 3ed66e910c91eb914b5c1f2d434538fe68bb8a56 Mon Sep 17 00:00:00 2001 From: Christoph Lameter Date: Mon, 7 Apr 2014 15:39:40 -0700 Subject: [PATCH] net: replace __this_cpu_inc in route.c with raw_cpu_inc The RT_CACHE_STAT_INC macro triggers the new preemption checks for __this_cpu ops. I do not see any other synchronization that would allow the use of a __this_cpu operation here however in commit dbd2915ce87e ("[IPV4]: RT_CACHE_STAT_INC() warning fix") Andrew justifies the use of raw_smp_processor_id() here because "we do not care" about races. In the past we agreed that the price of disabling interrupts here to get consistent counters would be too high. These counters may be inaccurate due to race conditions. The use of __this_cpu op improves the situation already from what commit dbd2915ce87e did since the single instruction emitted on x86 does not allow the race to occur anymore. However, non x86 platforms could still experience a race here. Trace: __this_cpu_add operation in preemptible [00000000] code: avahi-daemon/1193 caller is __this_cpu_preempt_check+0x38/0x60 CPU: 1 PID: 1193 Comm: avahi-daemon Tainted: GF 3.12.0-rc4+ #187 Call Trace: check_preemption_disabled+0xec/0x110 __this_cpu_preempt_check+0x38/0x60 __ip_route_output_key+0x575/0x8c0 ip_route_output_flow+0x27/0x70 udp_sendmsg+0x825/0xa20 inet_sendmsg+0x85/0xc0 sock_sendmsg+0x9c/0xd0 ___sys_sendmsg+0x37c/0x390 __sys_sendmsg+0x49/0x90 SyS_sendmsg+0x12/0x20 tracesys+0xe1/0xe6 Signed-off-by: Christoph Lameter Acked-by: David S. Miller Acked-by: Ingo Molnar Cc: Eric Dumazet Cc: Tejun Heo Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- net/ipv4/route.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/ipv4/route.c b/net/ipv4/route.c index 1be9e990514d..34d094cadb11 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -188,7 +188,7 @@ const __u8 ip_tos2prio[16] = { EXPORT_SYMBOL(ip_tos2prio); static DEFINE_PER_CPU(struct rt_cache_stat, rt_cache_stat); -#define RT_CACHE_STAT_INC(field) __this_cpu_inc(rt_cache_stat.field) +#define RT_CACHE_STAT_INC(field) raw_cpu_inc(rt_cache_stat.field) #ifdef CONFIG_PROC_FS static void *rt_cache_seq_start(struct seq_file *seq, loff_t *pos)