(netdev Cc:-ed)
* Christoph Lameter <[email protected]> wrote:
> These location triggered during testing with KVM.
>
> These are fetches without preemption off where we judged that
> to be more performance efficient or where other means of
> providing synchronization (BH handling) are available.
> Index: linux/include/net/snmp.h
> ===================================================================
> --- linux.orig/include/net/snmp.h 2013-09-12 13:26:29.216103951 -0500
> +++ linux/include/net/snmp.h 2013-09-12 13:26:29.208104037 -0500
> @@ -126,7 +126,7 @@ struct linux_xfrm_mib {
> extern __typeof__(type) __percpu *name[SNMP_ARRAY_SZ]
>
> #define SNMP_INC_STATS_BH(mib, field) \
> - __this_cpu_inc(mib[0]->mibs[field])
> + raw_cpu_inc(mib[0]->mibs[field])
>
> #define SNMP_INC_STATS_USER(mib, field) \
> this_cpu_inc(mib[0]->mibs[field])
> @@ -141,7 +141,7 @@ struct linux_xfrm_mib {
> this_cpu_dec(mib[0]->mibs[field])
>
> #define SNMP_ADD_STATS_BH(mib, field, addend) \
> - __this_cpu_add(mib[0]->mibs[field], addend)
> + raw_cpu_add(mib[0]->mibs[field], addend)
Are the networking folks fine with allowing unafe operations of SNMP stats
in preemptible sections, or should the kernel produce an optional warning
message if CONFIG_PREEMPT_DEBUG=y and these ops are used in preemptible
(non-bh, non-irq-handler, non-irqs-off, etc.) sections?
RAW_SNMP_*_STATS() ops could be used to annotate those places where that
kind of usage is safe.
Thanks,
Ingo
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