From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.tipi-net.de (mail.tipi-net.de [194.13.80.246]) (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 F1A5B4FE2F1; Tue, 13 Oct 2026 13:54:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=194.13.80.246 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791899687; cv=none; b=XfQQ66Z3xFeR0yAC8zsfOklJXxBY0Co0iiQdNPHfRKEFv30y74zaGDCaTaSHfbTSIb5n7rnmghV0u0jFJ25rHMbLtM1AK6FZl0oHY5igGGKHTofMxnQtd2ghxgqFHgsqPtfiEJHZAYbKwMIwIpoqkUEqzUh53wko9Equi6u6Zyw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791899687; c=relaxed/simple; bh=3PtGvoeT9m7Y4DmAr46TMvrMB44lIaxu8GMYoaFQUlI=; h=MIME-Version:Date:From:To:Cc:Subject:In-Reply-To:References: Message-ID:Content-Type; b=LzznRXlYYa0qbXZZTrr0Ly8u36fnfvUois3jE6vsAnJL4FhaziWhFAglaltbDMLBUQ3/E76TwIjLE7TaHg65O9mYFthsUEmga8SWWBsmhK6d3UQm5GeMVeb2R9okZt/jL8VOWrAKV7R2/P8ma4ic3ZGnS3PUMvwHARkGNYeoQNE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=tipi-net.de; spf=pass smtp.mailfrom=tipi-net.de; dkim=pass (2048-bit key) header.d=tipi-net.de header.i=@tipi-net.de header.b=vkOnxMQc; arc=none smtp.client-ip=194.13.80.246 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=tipi-net.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=tipi-net.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=tipi-net.de header.i=@tipi-net.de header.b="vkOnxMQc" Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id DCEADA05A6; Tue, 13 Oct 2026 15:54:41 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=tipi-net.de; s=dkim; t=1791899683; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=ggmQ0VJqPDmKU8eTBEH1GzV2i54bDKySbMFuZrvZpi4=; b=vkOnxMQck/dOnXagzX8Ga0MOiUAgYvpOFLSOrP+DkchS9G+w+MDytLH6U4cJWPCGV1AOXh PAANUVjl101XGVbn1SJc/PlyNlFY55xrnmUJypRhX3FlCvWKIzAgMtgMz9q0cNGstfbYxK 6a6Cu8KG8gyIjhH9F3JSgLrsEsLoDTt3yfpqWwPUu0QDujBOlQU6whTP0RpKDtm2eZvaR/ CzMKLUT/FD9XFkRUDw+7qXK7s4a3ALqBXZHiHleINTlH4e0UtX2W6VQL3XGCHtRQA/EvwH 8+RpprrfsyjzNzFD37PNE34LtGocr1snERmsS+AqaRFsF6qhSFp7lMbUeY0ZOA== Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Tue, 13 Oct 2026 15:54:41 +0200 From: Nicolai Buchwitz To: =?UTF-8?Q?Th=C3=A9o_Lebrun?= Cc: Conor Dooley , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Richard Cochran , Russell King , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Paolo Valerio , Vladimir Kondratiev , Gregory CLEMENT , =?UTF-8?Q?Beno=C3=AEt_Monin?= , Tawfik Bayouk , Thomas Petazzoni , stable+noautosel@kernel.org, Sashiko Subject: Re: [PATCH net-next v11 1/9] net: macb: close race between NAPI polls & ndo_stop In-Reply-To: <20261013-macb-context-v11-1-b27785167566@bootlin.com> References: <20261013-macb-context-v11-0-b27785167566@bootlin.com> <20261013-macb-context-v11-1-b27785167566@bootlin.com> Message-ID: <09659ad051e83174f82ecd74a4c9a49f@tipi-net.de> X-Sender: nb@tipi-net.de Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Last-TLS-Session-Version: TLSv1.3 Hi Théo On 13.10.2026 15:16, Théo Lebrun wrote: > In ndo_close, we call napi_disable() then free the ring buffers > queue->rx_ring|tx_ring. In the NAPI poll functions, after > napi_complete_done() we might enable interrupts and might re-check the > next ring buffer slot. > > This is a use-after-free race on our ring buffers because > napi_disable() > only waits for napi_complete_done() to return, it does not wait for > NAPI poll functions to finish. > > The poll function sequence must stay as-is, see commit 0bf476fc3624 > ("net: macb: Fix lost RX packet wakeup race in NAPI receive") which > explains why the sequence must be napi_complete_done() -> arm IRQs > -> re-check ring slot. > > Fix by waiting for full end of NAPI poll functions using > synchronize_net() in our ndo_close implementation. > > This bug has never been reproduced and was reported by Sashiko. The > chances of facing it in practice sound tiny: it needs a system without > any phylink attached, running PREEMPT_RT and with a kernel preemption > on the NAPI poll at the right instant. > > We fix it here before introducing context swapping, which is another > place where the race could appear (and Sashiko complains on this > series). > > Fixes: 138badbc21a0 ("net: macb: use NAPI for TX completion path") > Fixes: 1900e30d0ef7 ("net: macb: simplify/cleanup NAPI reschedule > checking") > Cc: stable+noautosel@kernel.org # too unlikely and never reported by > users > Reported-by: Sashiko > Link: > https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20261001-macb-context-v10-0-beb541bbb7df%40bootlin.com?part=7 > Link: > https://lore.kernel.org/all/179115680572.434549.1016291990685937691@kernel.org/ > Signed-off-by: Théo Lebrun > --- > drivers/net/ethernet/cadence/macb_main.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/drivers/net/ethernet/cadence/macb_main.c > b/drivers/net/ethernet/cadence/macb_main.c > index 020a47353d01..d414d00d93ce 100644 > --- a/drivers/net/ethernet/cadence/macb_main.c > +++ b/drivers/net/ethernet/cadence/macb_main.c > @@ -2059,6 +2059,12 @@ static void macb_quiesce_start(struct macb *bp) > napi_disable(&queue->napi_tx); > } > > + /* NAPI instances still access Rx/Tx rings after their > + * napi_complete_done() calls! Callers to macb_quiesce_start() > + * free rings, so wait for all NAPI handlers to be done. > + */ > + synchronize_net(); > + > /* Must be done after napi_tx is disabled: its completion re-arms > * the LPI timer. > */ Reviewed-by: Nicolai Buchwitz Thanks, Nicolai