From: Simon Horman <horms@kernel.org>
To: Nicolai Buchwitz <nb@tipi-net.de>
Cc: "Oliver Neukum" <oliver@neukum.org>,
"Andrew Lunn" <andrew+netdev@lunn.ch>,
"David S. Miller" <davem@davemloft.net>,
"Eric Dumazet" <edumazet@kernel.org>,
"Jakub Kicinski" <kuba@kernel.org>,
"Paolo Abeni" <pabeni@redhat.com>,
"Sjur Brændeland" <sjur.brandeland@stericsson.com>,
"Alexey Orishko" <alexey.orishko@gmail.com>,
"Bjørn Mork" <bjorn@mork.no>,
"Greg Suarez" <gsuarez@smithmicro.com>,
"Breno Leitao" <leitao@debian.org>,
linux-usb@vger.kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org,
"Mikkel Eskildsen" <mke@visotia.com>
Subject: Re: [PATCH net v2 1/2] net: usb: cdc_ncm: don't enable BHs in tx_fixup under netpoll
Date: Thu, 22 Oct 2026 13:58:14 +0100 [thread overview]
Message-ID: <20261022125814.GE708417@horms.kernel.org> (raw)
In-Reply-To: <20261021-cdc-ncm-netpoll-v2-1-8818965bbb69@tipi-net.de>
On Wed, Oct 21, 2026 at 09:56:18AM +0200, Nicolai Buchwitz wrote:
> netpoll holds the txq lock and calls ndo_start_xmit() with IRQs off but
> BHs on. The spin_unlock_bh() in cdc_ncm_tx_fixup() then runs pending
> softirqs. If one of them transmits, it spins on the txq lock that
> netpoll holds. With netconsole on a cdc_ncm device this ends in a soft
> or hard lockup.
>
> Use spin_lock_irqsave(), which is safe both under netpoll and on the
> normal xmit path.
>
> Fixes: c84ff1d6dff3 ("cdc_ncm: reduce driver latency in the data path")
> Reported-by: Mikkel Eskildsen <mke@visotia.com>
> Closes: https://lore.kernel.org/netdev/PRAP189MB185019A5A8D411482BB6E0CDA9982@PRAP189MB1850.EURP189.PROD.OUTLOOK.COM/
> Tested-by: Mikkel Eskildsen <mke@visotia.com>
> Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>
Reviewed-by: Simon Horman <horms@kernel.org>
next prev parent reply other threads:[~2026-10-22 12:58 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-21 7:56 [PATCH net v2 0/2] net: usb: cdc_ncm/cdc_mbim: fix netpoll lockup in tx_fixup Nicolai Buchwitz
2026-10-21 7:56 ` [PATCH net v2 1/2] net: usb: cdc_ncm: don't enable BHs in tx_fixup under netpoll Nicolai Buchwitz
2026-10-22 12:58 ` Simon Horman [this message]
2026-10-21 7:56 ` [PATCH net v2 2/2] net: usb: cdc_mbim: " Nicolai Buchwitz
2026-10-22 12:58 ` Simon Horman
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