From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792673900; b=DwJbkf4grAqPFB7o4quGpe9vECjsiTxe8wVz/tSw7iVxzx8PMGhaHo2qevEJdtJ2POtF AmgxMGjshUNlmpkG9HASeu7EYd2jUl4y7bWezVnbtPUfnNTFUhZpMF3k6BaXvGVI3q+XZ gLiuXQfjX6vB+OPk+EDb5+HiIgJVLHYqVODZ/yiDlAfY0rIXztjH9KQkX3WXwMAJPRAj+ 7PANL4xpnYHxMt7g9fOYcrL0eLa+ob9JaM7zaiw5xJS/l7d0Yif7QmDxyaLgAbqYyCQuA JlZEFWeJVXE//17UGSRtd/HKq3/csuzyga2yDLIp2iX5dUX7vGNfsu4XQEk7LVf7X1Q== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792673900; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=+y1K/aWGH6oaTGR8AaGUm8uDDh2ORJLAY2tcU/RT7Ss=; b=fgafRka5enJnBdn75UNcaUynFK3cyl8rUbok/q7dVLb/BQsZngkynYrNzYSBIPZbvker b79cOIMeOftfnabNccSah/vLdocCdRLuvVqH+fTXaK7/dO8E/2j20LGFi8g4EBWHNvtn+ eSgoTiFgdOO69y5oZ5CbpkPGqbJMXpfTJ3sMC2zzigSkN1A/NfwxyBEf0Ug7cnToqcFEE 4hXeoUO6NJOdp0oGo4+4JIxaDAMbIWpR3VebNTeZlIbvhmdHpKWeJ7rsjlJ4aLRlkRmH7 wK1owHDpI6yNeYzqNSxLnbFKNLj+0n+i1QsY182+cJyaq0z6zdzlcu6phL+Y1V2uqNw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=SOQZ1Dse; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C94E9606A320; Thu, 22 Oct 2026 12:58:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=SOQZ1Dse Received: by smtp.kernel.org (Postfix) with ESMTPSA id A9A1B1F000C2; Thu, 22 Oct 2026 12:58:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792673899; bh=+y1K/aWGH6oaTGR8AaGUm8uDDh2ORJLAY2tcU/RT7Ss=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=SOQZ1DseXpQrKmekZL3IEfrzzRNZ81u3L1vRcm9BznD/+56innnLAQ1Yca0yDYtKb VXgHJ3cO5dOt/3Etib/aeAWd9fD97Ni7LMIhKOhp5ML57Ejt66VrAeaP3mU4b+wGq7 vqUEqSInv3EyNpsDt7nlqgg5sR9bDpRb7PZJYgb8yPzXUEIP0Px7o24L7R/0RkV5jz UK5ty0rMjGih5MBQgdonyf+oIdMzlinnbKmsYktCYXLtiHWtx+oU3JJbVCq0BP8wNE +gF8zMpufhLrPqVbL5kw4Jmuse34QzsCQs0TG4nfpb+Noabp8ReVGgzK/eDy0qF2SU tWCciq6C2NVOQ== Date: Thu, 22 Oct 2026 13:58:14 +0100 From: Simon Horman To: Nicolai Buchwitz Cc: Oliver Neukum , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Sjur =?utf-8?Q?Br=C3=A6ndeland?= , Alexey Orishko , =?utf-8?B?QmrDuHJu?= Mork , Greg Suarez , Breno Leitao , linux-usb@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Mikkel Eskildsen Subject: Re: [PATCH net v2 1/2] net: usb: cdc_ncm: don't enable BHs in tx_fixup under netpoll Message-ID: <20261022125814.GE708417@horms.kernel.org> References: <20261021-cdc-ncm-netpoll-v2-0-8818965bbb69@tipi-net.de> <20261021-cdc-ncm-netpoll-v2-1-8818965bbb69@tipi-net.de> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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 > Closes: https://lore.kernel.org/netdev/PRAP189MB185019A5A8D411482BB6E0CDA9982@PRAP189MB1850.EURP189.PROD.OUTLOOK.COM/ > Tested-by: Mikkel Eskildsen > Signed-off-by: Nicolai Buchwitz Reviewed-by: Simon Horman