From: Eric Dumazet <[email protected]>
Date: Wed, 02 Sep 2015 15:48:57 -0700
> On Wed, 2015-09-02 at 14:52 -0700, Martin KaFai Lau wrote:
>> On Wed, Sep 02, 2015 at 02:30:45PM -0700, Eric Dumazet wrote:
>> > Object cannot be freed until all cpus have exited their RCU sections.
>> You meant the dst_destroy() here will wait for all cpus exited their RCU
>> sections?
>>
>> static inline void dst_free(struct dst_entry *dst)
>> {
>> if (dst->obsolete > 0)
>> return;
>> if (!atomic_read(&dst->__refcnt)) {
>> dst = dst_destroy(dst);
>> if (!dst)
>> return;
>> }
>> __dst_free(dst);
>> }
>
> dst_free() is called after RCU grace period, in the case you are
> interested in.
>
> Look at dst_rcu_free() and rt_free()
For ipv4, this is true, but in ipv6, it is not necessarily done in
this way. And I think that is the point Martin is trying to make.
If you look, the dst_free() calls in ipv6 are basically synchronous,
it does not use dst_rcu_free().
And thus, the fix is to make ipv6 properly RCU free route entries.
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