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 dbd2915ce8 ("[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
dbd2915ce8 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 <cl@linux.com>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Ingo Molnar <mingo@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
3ed66e910c