From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3CEB7C433F5 for ; Mon, 10 Oct 2022 15:37:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229725AbiJJPhS (ORCPT ); Mon, 10 Oct 2022 11:37:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54174 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229487AbiJJPhQ (ORCPT ); Mon, 10 Oct 2022 11:37:16 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5C88771BC5; Mon, 10 Oct 2022 08:37:15 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id ED6C660F69; Mon, 10 Oct 2022 15:37:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 293DBC433C1; Mon, 10 Oct 2022 15:37:13 +0000 (UTC) Authentication-Results: smtp.kernel.org; dkim=pass (1024-bit key) header.d=zx2c4.com header.i=@zx2c4.com header.b="ppcXTPB+" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zx2c4.com; s=20210105; t=1665416231; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=sBj5n8AeywXS5nBd6mMPaCC8APWIC2bqj8ZV7OMzNDI=; b=ppcXTPB+D/rSVYbNWHtYjGfYdaN+yA7n5mGjk25di8AVpcNxtQSABFIFG1CpPPJbIXU4tl MU+fr/ns+9f2eNYvubOh9Row2wL/0AnrM39wFla0zzfBjmFiuA0Ana3LVk18Wnb/uyRa25 jck+BzVaDZYmAgC6aK77KsFdlzNReII= Received: by mail.zx2c4.com (ZX2C4 Mail Server) with ESMTPSA id 3616f1ca (TLSv1.3:TLS_AES_256_GCM_SHA384:256:NO); Mon, 10 Oct 2022 15:37:11 +0000 (UTC) Date: Mon, 10 Oct 2022 09:37:07 -0600 From: "Jason A. Donenfeld" To: Mark Brown , Florian Fainelli , Dominik Brodowski , Herbert Xu , kernelci-results@groups.io, bot@kernelci.org, gtucker@collabora.com, linux-arm-kernel@lists.infradead.org, linux-rpi-kernel@lists.infradead.org, bcm-kernel-feedback-list@broadcom.com, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] hw_random: bcm2835: use hwrng_msleep() instead of cpu_relax() Message-ID: References: <20221010150607.720600-1-Jason@zx2c4.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20221010150607.720600-1-Jason@zx2c4.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 10, 2022 at 09:06:07AM -0600, Jason A. Donenfeld wrote: > Rather than busy looping, yield back to the scheduler and sleep for a > bit in the event that there's no data. This should hopefully prevent the > stalls that Mark reported: > > <6>[ 3.362859] Freeing initrd memory: 16196K > <3>[ 23.160131] rcu: INFO: rcu_sched self-detected stall on CPU > <3>[ 23.166057] rcu: 0-....: (2099 ticks this GP) idle=03b4/1/0x40000002 softirq=28/28 fqs=1050 > <4>[ 23.174895] (t=2101 jiffies g=-1147 q=2353 ncpus=4) > <4>[ 23.180203] CPU: 0 PID: 49 Comm: hwrng Not tainted 6.0.0 #1 > <4>[ 23.186125] Hardware name: BCM2835 > <4>[ 23.189837] PC is at bcm2835_rng_read+0x30/0x6c > <4>[ 23.194709] LR is at hwrng_fillfn+0x71/0xf4 > <4>[ 23.199218] pc : [] lr : [] psr: 40000033 > <4>[ 23.205840] sp : f093df70 ip : 00000000 fp : 00000000 > <4>[ 23.211404] r10: c3c7e800 r9 : 00000000 r8 : c17e6b20 > <4>[ 23.216968] r7 : c17e6b64 r6 : c18b0a74 r5 : c07ccd99 r4 : c3f171c0 > <4>[ 23.223855] r3 : 000fffff r2 : 00000040 r1 : c3c7e800 r0 : c3f171c0 > <4>[ 23.230743] Flags: nZcv IRQs on FIQs on Mode SVC_32 ISA Thumb Segment none > <4>[ 23.238426] Control: 50c5387d Table: 0020406a DAC: 00000051 > <4>[ 23.244519] CPU: 0 PID: 49 Comm: hwrng Not tainted 6.0.0 #1 > > Link: https://lore.kernel.org/all/Y0QJLauamRnCDUef@sirena.org.uk/ > Signed-off-by: Jason A. Donenfeld > --- > I haven't tested this. Somebody with access to that kernel CI infra that > triggered this will need to test. So I succeeded at testing this, sort of. I was able to reproduce the hang on a CONFIG_PREEMPT=n kernel with this diff: diff --git a/drivers/net/wireguard/main.c b/drivers/net/wireguard/main.c index ee4da9ab8013..19e1186f0db0 100644 --- a/drivers/net/wireguard/main.c +++ b/drivers/net/wireguard/main.c @@ -15,12 +15,29 @@ #include #include #include +#include #include +static int derp_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait) +{ + if (wait) { + for (;;) + cpu_relax(); + } + return 0; +} + +static struct hwrng derp_ops = { + .name = "flurpderp", + .read = derp_rng_read, +}; + static int __init wg_mod_init(void) { int ret; + hwrng_register(&derp_ops); + ret = wg_allowedips_slab_init(); if (ret < 0) goto err_allowedips; Next, I changed the cpu_relax() into hwrng_msleep(), as this patch does: diff --git a/drivers/net/wireguard/main.c b/drivers/net/wireguard/main.c index ee4da9ab8013..19e1186f0db0 100644 --- a/drivers/net/wireguard/main.c +++ b/drivers/net/wireguard/main.c @@ -15,12 +15,29 @@ #include #include #include +#include #include +static int derp_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait) +{ + if (wait) { + for (;;) + hwrng_msleep(rng, 1000); + } + return 0; +} + +static struct hwrng derp_ops = { + .name = "flurpderp", + .read = derp_rng_read, +}; + static int __init wg_mod_init(void) { int ret; + hwrng_register(&derp_ops); + ret = wg_allowedips_slab_init(); if (ret < 0) goto err_allowedips; And then the problem went away. So I think this patch is a good one. Jason