From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 318EF30C613; Mon, 16 Feb 2026 12:11:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771243905; cv=none; b=f4X+HDeCWHJGULlrQpEyiPE6V4n5UKLFdpoE9KAuMCTcJ0SvAV2UY1XnVoJ79BAbz+9TxT5TMPak4c9gFp4lEC9MDlou6RMwWVtJFhgj8oTgbfuopBoZoworBbqyncQX96gE/huLpgxVWNBKX0A03ilrjTa80nBQaFmxTNQduzI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1771243905; c=relaxed/simple; bh=VrzPRqY2WAT6Xt7UjSu8aww5moulArYPq1BlYuYkS9Q=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ZLnslJlBL7EHXyU8Ei9BphqYntL2bYf6U9WqWn/GO8+4hiDv/LTTGbmglF6jW9yNavUExNbeYCcvPEbLIZoGuNPQLdP/XRWNjy4nCku9JXgDxJ/KJsiOb25I0M5NQuCsiz7wGwnXiS144lrTNWDsLJL+UjALb4mbyRuj9rM+ihY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=LOFLYMeq; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="LOFLYMeq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AF2AAC19423; Mon, 16 Feb 2026 12:11:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1771243904; bh=VrzPRqY2WAT6Xt7UjSu8aww5moulArYPq1BlYuYkS9Q=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=LOFLYMeqWPd4M5tToXP5cuD0dGmL+Rlcvcl/DjcdlTeUQJ4RGOzXNur28NDZSe9TK iDrPinK0s0tEoJ0hAJe3be+PUchsT5De8xjEzgRXa2EUREtNSKTYvFdx6UZCVEKix4 YXaL2wZEyjE2Sb+jneFANXDWbkG8wNpJwqS9PXVhm7/Qv9PIcRYhXiguX9bT9wGw9P Gbs7b2fmfolVQHrRRvt2Ndg8X2EqwtRmVDZJka5zJp9GKLI4D4sX/G5uZp3JwbRAoP IxdNxDMcZIUZinDYhS0yYgSteSa2MNj0qP7GX5pMPu5/TB7s3OQ2g6LdXVMJxt4YvL +4NknfF+DL6Xg== Date: Mon, 16 Feb 2026 12:11:40 +0000 From: Simon Horman To: Jakub Kicinski Cc: davem@davemloft.net, netdev@vger.kernel.org, edumazet@google.com, pabeni@redhat.com, andrew+netdev@lunn.ch, shuah@kernel.org, marcelo.leitner@gmail.com, jhs@mojatatu.com, dcaratti@redhat.com, linux-kselftest@vger.kernel.org Subject: Re: [PATCH net] selftests: tc_actions: don't dump 2MB of \0 to stdout Message-ID: References: <20260214035159.2119699-1-kuba@kernel.org> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260214035159.2119699-1-kuba@kernel.org> On Fri, Feb 13, 2026 at 07:51:59PM -0800, Jakub Kicinski wrote: > Since we started running selftests in NIPA we have been seeing > tc_actions.sh generate a soft lockup warning on ~20% of the runs. > On the pre-netdev foundation setup it was actually a missed irq > splat from the console. Now it's either that or a lockup. > > I initially suspected a socket locking issue since the test > is exercising local loopback with act_mirred. > After hours of staring at this I noticed in strace that ncat Ouch! > when -o $file is specified _both_ saves the output to the file > and still prints it to stdout. Because the file being sent > is constructed with: > > dd conv=sparse status=none if=/dev/zero bs=1M count=2 of=$mirred > ^^^^^^^^^ > > the data printed is all \0. Most terminals don't display nul > characters (and neither does vng output capture save them). > But QEMU's serial console still has to poke them thru which > is very slow and causes the lockup (if the file is >600kB). > > Replace the '-o $file' with '> $file'. This speeds the test up > from 2m20s to 18s on debug kernels, and prevents the warnings. > > Fixes: ca22da2fbd69 ("act_mirred: use the backlog for nested calls to mirred ingress") > Signed-off-by: Jakub Kicinski I exercise this by running ncat locally on Fedora 43. $ ncat --version Ncat: Version 7.92 ( https://nmap.org/ncat ) And confirmed the behaviour you describe. Reviewed-by: Simon Horman