On 2018年05月25日 21:43, Toshiaki Makita wrote:
[...]
@@ -1917,16 +1923,22 @@ static ssize_t tun_get_user(struct
tun_struct *tun, struct tun_file *tfile,
struct bpf_prog *xdp_prog;
int ret;
+ local_bh_disable();
+ preempt_disable();
rcu_read_lock();
xdp_prog = rcu_dereference(tun->xdp_prog);
if (xdp_prog) {
ret = do_xdp_generic(xdp_prog, skb);
if (ret != XDP_PASS) {
rcu_read_unlock();
+ preempt_enable();
+ local_bh_enable();
return total_len;
}
}
rcu_read_unlock();
+ preempt_enable();
+ local_bh_enable();
}
rcu_read_lock();
Good catch, thanks.
But I think we can just replace preempt_disable()/enable() with
local_bh_disable()/local_bh_enable() ?
I actually thought the same, but noticed this patch.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9ea4c380066fbe
It looks like they do not think local_bh_disable() implies
preempt_disable(). But I'm not sure why..
Toshiaki Makita
I see, there're probably have some subtle differences and implications
for e.g scheduler or others.
What we what here is to make sure the process is not moved to another
CPU and bh is enabled. By checking preemptible() function, preemption
should be disabled after local_bh_disable(). So I think we're safe here.
Thanks
