netdev - Re: [PATCH bpf-next 06/17] bnxt: remove rcu_read

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20210609135834.GC4397@paulmck-ThinkPad-P17-Gen-1>
Date:   Wed, 9 Jun 2021 06:58:34 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org,
        Martin KaFai Lau <kafai@...com>,
        Hangbin Liu <liuhangbin@...il.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Magnus Karlsson <magnus.karlsson@...il.com>,
        Michael Chan <michael.chan@...adcom.com>
Subject: Re: [PATCH bpf-next 06/17] bnxt: remove rcu_read_lock() around XDP
 program invocation

On Wed, Jun 09, 2021 at 12:33:15PM +0200, Toke Høiland-Jørgensen wrote:
> The bnxt 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.

And same for the rest of these removals.  Someone might be very happy
to have that comment at some later date, and that someone just might
be you.  ;-)

							Thanx, Paul

> Cc: Michael Chan <michael.chan@...adcom.com>
> Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
> ---
>  drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
> index ec9564e584e0..bee6e091a997 100644
> --- a/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
> +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_xdp.c
> @@ -138,9 +138,7 @@ bool bnxt_rx_xdp(struct bnxt *bp, struct bnxt_rx_ring_info *rxr, u16 cons,
>  	xdp_prepare_buff(&xdp, *data_ptr - offset, offset, *len, false);
>  	orig_data = xdp.data;
>  
> -	rcu_read_lock();
>  	act = bpf_prog_run_xdp(xdp_prog, &xdp);
> -	rcu_read_unlock();
>  
>  	tx_avail = bnxt_tx_avail(bp, txr);
>  	/* If the tx ring is not full, we must not update the rx producer yet
> -- 
> 2.31.1
>