Subject: Re: [PATCH bpf-next v3 15/16] stmmac: remove rcu_read_lock() around XDP program invocation

From: Wong Vee Khee <[email-masked]>
Date: Fri, 18 Jun 2021 17:47:35 +0800

On Thu, Jun 17, 2021 at 11:27:47PM +0200, Toke Høiland-Jørgensen wrote:
> The stmmac driver has rcu_read_lock()/rcu_read_unlock() pairs around XDP
> program invocations. However, the actual lifetime of the objects referred
> by the XDP program invocation is longer, all the way through to the call to
> xdp_do_flush(), making the scope of the rcu_read_lock() too small. This
> turns out to be harmless because it all happens in a single NAPI poll
> cycle (and thus under local_bh_disable()), but it makes the rcu_read_lock()
> misleading.
> 
> Rather than extend the scope of the rcu_read_lock(), just get rid of it
> entirely. With the addition of RCU annotations to the XDP_REDIRECT map
> types that take bh execution into account, lockdep even understands this to
> be safe, so there's really no reason to keep it around.
> 
> Cc: Giuseppe Cavallaro <[email-masked]>
> Cc: Alexandre Torgue <[email-masked]>
> Cc: Jose Abreu <[email-masked]>
> Signed-off-by: Toke Høiland-Jørgensen <[email-masked]>

Acked-by: Wong Vee Khee <[email-masked]>
Tested-by: Song, Yoong Siang <[email-masked]>

> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 13 +++++--------
>  1 file changed, 5 insertions(+), 8 deletions(-)