From: sashiko-bot@kernel.org
To: "Nicolai Buchwitz" <nb@tipi-net.de>
Cc: linux-usb@vger.kernel.org
Subject: Re: [PATCH net v3 1/2] net: usb: cdc_ncm: don't enable BHs in tx_fixup under netpoll
Date: Sat, 24 Oct 2026 13:33:37 +0000 [thread overview]
Message-ID: <sashiko-outbox-183742@kernel.org> (raw)
In-Reply-To: <20261024-cdc-ncm-netpoll-v3-1-6284ca03f967@tipi-net.de>
> 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.
>
> Every caller of cdc_ncm_tx_fixup() holds the txq lock with BHs or IRQs
> off, so the softirq user of ctx->mtx cannot interrupt it. Use plain
> spin_lock().
>
> 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/
> Signed-off-by: Nicolai Buchwitz <nb@tipi-net.de>
Sashiko has reviewed this patch and found no issues.
--
Sashiko AI review · https://sashiko.dev/#/patchset/20261024-cdc-ncm-netpoll-v3-0-6284ca03f967@tipi-net.de?part=1
next prev parent reply other threads:[~2026-10-24 13:33 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-24 13:23 [PATCH net v3 0/2] net: usb: cdc_ncm/cdc_mbim: fix netpoll lockup in tx_fixup Nicolai Buchwitz
2026-10-24 13:23 ` [PATCH net v3 1/2] net: usb: cdc_ncm: don't enable BHs in tx_fixup under netpoll Nicolai Buchwitz
2026-10-24 13:33 ` sashiko-bot [this message]
2026-10-24 13:23 ` [PATCH net v3 2/2] net: usb: cdc_mbim: " Nicolai Buchwitz
2026-10-24 13:33 ` sashiko-bot
2026-10-27 1:40 ` [PATCH net v3 0/2] net: usb: cdc_ncm/cdc_mbim: fix netpoll lockup in tx_fixup patchwork-bot+netdevbpf
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