From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-182.mta1.migadu.com (out-182.mta1.migadu.com [95.215.58.182]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A70AD2E414 for ; Tue, 3 Mar 2026 23:42:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772581346; cv=none; b=HabL7OroGyWZCjz+Gp3M6aC8N8gSvmWHGShshpHI14ndiLzMNqdJfnS+eMEdjPPKuIdFqaZUMryyrrWL369K6jQ/EFI650UeGuNFTyPtu37qdoRoDK15DJBgMVrS35nmbsrME7YVdWK2AqWGkkpOzmyFTqz8fiUvoZjIdtAQLos= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772581346; c=relaxed/simple; bh=kWhijkX4NW9+j8hjQNKVNHbTc1OwH2G//Ljxi1C9zNk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lTF5mbLInZ7HbVTmUQ/WOwDOlmXajDLyvQrqjtxL1Ud4knAGh/eWXMW1xZ48XXpNWj2YyPA1epJ4R+eM+uxnB35jP0l4tr0IFk482Cw2fB1o3D8i6RzZX2gnpQXwDFk0/5pX5LrzOLGfFYp9V60lKp1vW4VOTqK8qA/qM9AkOqw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=WiuJU9xS; arc=none smtp.client-ip=95.215.58.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="WiuJU9xS" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1772581341; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=GZ/CIewNUhK4DMFEo8Ql83aiKEIEGzE6lChFBdbn6Qw=; b=WiuJU9xSpPqUUi0fFmsaSFfdclDs2RnncKi0uexKiZV2/5T4+rQp/AV0D0U+vMuHTPOnJM SQNP2pe4y/+PsPJyUZh/iG8WrSk9ez3KpnRawQZA4Mp7+lrQvzE25mPhAWdLfESidtEZmP QJrH2E7Ss/GwiBZHXDJ5i6lPo3pa2YI= Date: Tue, 3 Mar 2026 15:42:12 -0800 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v1 bpf-next] net: core: allow netdev_upper_get_next_dev_rcu from bh context To: Jakub Kicinski , Kohei Enju Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, "David S. Miller" , Eric Dumazet , Paolo Abeni , Simon Horman , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , =?UTF-8?Q?Toke_H=C3=B8iland-J=C3=B8rgensen?= , kohei.enju@gmail.com References: <20260220110922.94781-1-kohei@enjuk.jp> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau In-Reply-To: <20260220110922.94781-1-kohei@enjuk.jp> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT On 2/20/26 3:09 AM, Kohei Enju wrote: > Since XDP programs are called from a NAPI poll context, the RCU > reference liveness is ensured by local_bh_disable(). > > Commit aeea1b86f936 ("bpf, devmap: Exclude XDP broadcast to master > device") started to call netdev_upper_get_next_dev_rcu() from this > context, but missed adding rcu_read_lock_bh_held() as a condition to the > RCU checks. > While both bh_disabled and rcu_read_lock() provide RCU protection, > lockdep complains since the check condition is insufficient [1]. > > Add rcu_read_lock_bh_held() as condition to help lockdep to understand > the dereference is safe, in the same way as commit 694cea395fde ("bpf: > Allow RCU-protected lookups to happen from bh context"). > > [1] > WARNING: net/core/dev.c:8099 at netdev_upper_get_next_dev_rcu+0x96/0xd0, CPU#0: swapper/0/0 > ... > RIP: 0010:netdev_upper_get_next_dev_rcu+0x96/0xd0 > ... > > dev_map_enqueue_multi+0x411/0x970 > xdp_do_redirect+0xdf2/0x1030 > __igc_xdp_run_prog+0x6a0/0xc80 > igc_poll+0x34b0/0x70b0 > __napi_poll.constprop.0+0x98/0x490 > net_rx_action+0x8f2/0xfa0 > handle_softirqs+0x1c7/0x710 > __irq_exit_rcu+0xb1/0xf0 > irq_exit_rcu+0x9/0x20 > common_interrupt+0x7f/0x90 > > > Signed-off-by: Kohei Enju > --- > net/core/dev.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/net/core/dev.c b/net/core/dev.c > index 096b3ff13f6b..b99d46b682c6 100644 > --- a/net/core/dev.c > +++ b/net/core/dev.c > @@ -8103,7 +8103,8 @@ struct net_device *netdev_upper_get_next_dev_rcu(struct net_device *dev, > { > struct netdev_adjacent *upper; > > - WARN_ON_ONCE(!rcu_read_lock_held() && !lockdep_rtnl_is_held()); > + WARN_ON_ONCE(!rcu_read_lock_held() && !rcu_read_lock_bh_held() && lgtm after re-reading some of the threads related to commit 694cea395fde. Jakub, if it looks good to you also, can you take it to the net-next tree? Thanks. Acked-by: Martin KaFai Lau > + !lockdep_rtnl_is_held()); > > upper = list_entry_rcu((*iter)->next, struct netdev_adjacent, list); >