From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 9676536A009; Mon, 12 Oct 2026 08:58:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791795492; cv=none; b=NFvZ5tQVRVfXFjlUGOmrrjDg92QJK1usQ7lUn9eqQD2kPRpgqas/uIczxlbV/uoeo70nC8cz/z+6UTRE47wv1oTyr6sKmS5hoBL7ip6rBkIS13SvJhd7izk0i1NI1CaXSLUiN7JePxthW2enucrNqBOhULLdeEbj/AnGaDcMV9I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791795492; c=relaxed/simple; bh=30VFGCRA0qJB0Bq1PBBcD4DWnr/FP3m5761PkCZqa38=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=W2I/Rty27c//S8hBfMZxNKTE9bVnU8B2BNGgWBJwQLVpOdgOi1ayESLLi+QnCnK8Gu89UPXzGwrkImYC9gAEuQpDphgljl2UA8blMJVMj6PRR+tAP7x8+US/m8oDkG43b6Wl5K8I6NIzAfIham64fzBOBJvxzKeRxg+3c7CxoTs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=ZwaqRO+A; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=BIj6kN4l; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="ZwaqRO+A"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="BIj6kN4l" From: Kurt Kanzenbach DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1791795488; 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: in-reply-to:in-reply-to:references:references; bh=lEhppZbolJBBfUeHZTohEYrvVBHJFyiflHzlpvjk9QY=; b=ZwaqRO+AkpSt8dmvPcJKjxaAhjQqh1xmhmr2sVDa3CSZo7pgZbtlQ5JSC2lA1aSpULfjB+ KKDUaazdj9Ax24BADaroUKqsZW7XBKQcMwInH2sIe/4rujkF+l7mLIhX/cM0MBjDyR/yGF 9Rpz/mQtyeQ94swd4bDOqWukW/0+mVh/GvPUdqf+SSUz3X/OpjonTU7AvnzrKdgCNjV+9K UKxj+h3bKPze02npvbVBZqp0CA6p9H0hX1FUFx9roJpmUZrCwZZ/AWG2hjSEGKv1DMHgqf 8AeextzcuGB+Oco2Q2j2nDlfvYx3ScvtWIv8yx7SF0nU5vKw+SJuMNvmPkJfog== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1791795488; 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: in-reply-to:in-reply-to:references:references; bh=lEhppZbolJBBfUeHZTohEYrvVBHJFyiflHzlpvjk9QY=; b=BIj6kN4lEHbjxXiTrT+37wQM8K+6Afcl/eks2A4k2ZATpXO7IU6m7ME5XDz5/kMWncAJB0 b0Vn6A3T6/h9UFCw== To: netdev-bot+sashiko@kernel.org Cc: maxime.chevallier@bootlin.com, andrew+netdev@lunn.ch, davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, edumazet@kernel.org, mcoquelin.stm32@gmail.com, alexandre.torgue@foss.st.com, ast@kernel.org, daniel@iogearbox.net, hawk@kernel.org, john.fastabend@gmail.com, sdf@fomichev.me, yoong.siang.song@intel.com, noor.azura.ahmad.tarmizi@intel.com, faizal.abdul.rahim@intel.com, boon.leong.ong@intel.com, bigeasy@linutronix.de, netdev@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, linux-arm-kernel@lists.infradead.org, bpf@vger.kernel.org Subject: Re: [PATCH net v2 1/2] net: stmmac: Disable NAPI before stopping Tx queues in stmmac_xdp_release() In-Reply-To: <179148659257.434549.8899547962974012240@kernel.org> References: <20261005-stmmac_xsk_crashes-v2-1-46c60cba6421@linutronix.de> <179148659257.434549.8899547962974012240@kernel.org> Date: Mon, 12 Oct 2026 10:58:06 +0200 Message-ID: <878q43gush.fsf@jax.kurt.home> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha512; protocol="application/pgp-signature" --=-=-= Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On Thu Oct 08 2026, netdev-bot+sashiko@kernel.org wrote: > Thank you for your contribution! Sashiko AI review found 2 potential > issue(s) to consider. > > Critical: 0 =C2=B7 High: 2 (1) =C2=B7 Medium: 0 (1) =C2=B7 Low: 0 > > If you believe none of the issues are legitimate, please reply to each > issue of Medium severity or higher and explain why the AI is wrong. > If any of them are legitimate and you plan to respin, please let patchwork > know by including "pw-bot: cr" as a separate line at the end of your reply > (one such reply per series is enough). > > - [High] Baseline decision: false. > - [High] This patch reorders stmmac_xdp_release() so that > hrtimer_cancel() on every tx_q->txtimer now runs before=E2=80=A6 > > Pre-existing issues: > - [High] This problem was not introduced by this patch, but it is a use- > after-free in the same teardown sequence, and moving=E2=80=A6 > - [Medium] Baseline decision: false. > > -- > > net: stmmac: Disable NAPI before stopping Tx queues in stmmac_xdp_release= () > > This commit reorders stmmac_xdp_release() so that NAPI is disabled and the > Tx coalescing timers are cancelled before netif_tx_disable() is called. > The goal is to stop an in-flight Tx NAPI poll from waking the Tx queue > again while free_dma_desc_resources() releases the descriptor rings. > >> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers= /net/ethernet/stmicro/stmmac/stmmac_main.c >> index 9741f97fa37a2..796817caf7af0 100644 >> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c >> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c >> @@ -7178,15 +7178,15 @@ void stmmac_xdp_release(struct net_device *dev) >> struct stmmac_priv *priv =3D netdev_priv(dev); >> u8 chan; >>=20=20 >> - /* Ensure tx function is not running */ >> - netif_tx_disable(dev); >> - >> /* Disable NAPI process */ >> stmmac_disable_all_queues(priv); >>=20=20 >> for (chan =3D 0; chan < priv->plat->tx_queues_to_use; chan++) >> hrtimer_cancel(&priv->dma_conf.tx_queue[chan].txtimer); >>=20=20 >> + /* Ensure tx function is not running */ >> + netif_tx_disable(dev); > > [Severity: High] > Now that netif_tx_disable() runs after the hrtimer_cancel() loop, can > stmmac_xmit() re-arm tx_q->txtimer after it has been cancelled? > > Before this change, netif_tx_disable() took every txq lock first. Any > running stmmac_xmit() had finished and the queues were stopped before the > timers were cancelled. > > Now stmmac_xmit() can run at the same time as stmmac_disable_all_queues() > and the cancel loop. It always ends by calling stmmac_tx_timer_arm(): > > stmmac_tx_timer_arm() { > ... > if (unlikely(!napi_is_scheduled(napi))) { > if (unlikely(!(hrtimer_active(&tx_q->txtimer)))) > hrtimer_start(&tx_q->txtimer, > STMMAC_COAL_TIMER(tx_coal_timer), > HRTIMER_MODE_REL); > ... > } > > One possible interleaving: > > CPU1 (stmmac_xmit) CPU0 (stmmac_xdp_release) > stmmac_tx_timer_arm() > napi_is_scheduled() =3D=3D false > stmmac_disable_all_queues() > napi_disable() sets SCHED > hrtimer_cancel(&tx_q->txtimer) > timer not armed, returns 0 > hrtimer_start(&tx_q->txtimer) > netif_tx_disable(dev) > > The timer then stays queued while the rings are freed. The timeout is 5ms > by default and up to 100ms through ethtool -C tx-usecs. > > stmmac_xdp_set_prog() then calls stmmac_xdp_open(), which does: > > hrtimer_setup(&tx_q->txtimer, stmmac_tx_timer, CLOCK_MONOTONIC, HRTIMER_= MODE_REL); > > __hrtimer_setup() memsets the timer while it is still linked in the > hrtimer base timerqueue. > > Could that corrupt the timerqueue rbtree when the timer expires or is > started again? > > Would this order avoid the problem: disable NAPI, then netif_tx_disable(), > then hrtimer_cancel()? > > __stmmac_release() is cited in the commit message as the reference order, > but it also cancels the timers before netif_tx_disable(). It may have the > same window. Looks like a possible issue even though I did not observe this. The common cleanup code between stmmac_xdp_release() and __stmmac_release() can be moved into a helper function in a later patch. This issue can be addressed then. > > [Severity: High] > The reproducer in the commit message opens an AF_XDP/ZC socket. When an > XDP program is already attached, that goes through stmmac_xdp_setup_pool() > -> stmmac_xdp_enable_pool() in stmmac_xdp.c, not stmmac_xdp_release(): > > stmmac_xdp_enable_pool() { > ... > if (need_update) { > napi_disable(&ch->rx_napi); > napi_disable(&ch->tx_napi); > stmmac_disable_rx_queue(priv, queue); > stmmac_disable_tx_queue(priv, queue); > } > ... > } > > stmmac_disable_tx_queue() frees the ring with stmmac_stop_tx_dma() and > __free_dma_tx_desc_resources(). Nothing stops the netdev Tx queue. > stmmac_xdp_disable_pool() follows the same pattern with ch->rxtx_napi. > > At this commit, can stmmac_xmit() keep writing into tx_q->dma_tx while the > ring is freed and reallocated on these paths? > > The next patch in the series, "net: stmmac: Stop Tx queue when > (en|dis)abling XSK pools", appears to address this. It adds > stmmac_xdp_stop_tx_queue() after napi_disable() and netif_tx_wake_queue() > after the queues are re-enabled, which closes the gap by the end of the > series. Yes, that's fixed in the second patch. > >> + >> /* Free the IRQ lines */ >> stmmac_free_irq(dev, REQ_IRQ_ERR_ALL, 0); > > [Severity: Medium] > This isn't a bug introduced by this patch, but the TX/DMA IRQ handlers > stay registered after netif_tx_disable() until stmmac_free_irq() runs. > STMMAC_DOWN is not set on this path. > > If a TX hard error arrives in that window, stmmac_msi_intr_tx() or > stmmac_dma_interrupt() calls stmmac_tx_err(), which ends with: > > stmmac_tx_err() { > ... > priv->xstats.tx_errors++; > netif_tx_wake_queue(netdev_get_tx_queue(priv->dev, chan)); > } > > Can that reopen the queue so that stmmac_xmit() runs on rings that > free_dma_desc_resources() is about to release? > > The window existed before this patch and was larger then. Hitting it needs > a hardware DMA TX fatal error during XDP attach or detach. Yes, i did not observe this while testing. > > [Severity: High] > This is a pre-existing issue, not introduced by this patch. Moving > netif_tx_disable() does not change it. Yes, that's a separate issue. 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