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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BEE39C433EF for ; Mon, 1 Nov 2021 10:06:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A043561051 for ; Mon, 1 Nov 2021 10:06:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232298AbhKAKJN (ORCPT ); Mon, 1 Nov 2021 06:09:13 -0400 Received: from smtp-out2.suse.de ([195.135.220.29]:39852 "EHLO smtp-out2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231958AbhKAKI6 (ORCPT ); Mon, 1 Nov 2021 06:08:58 -0400 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out2.suse.de (Postfix) with ESMTP id 4C6491FD29; Mon, 1 Nov 2021 10:06:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1635761184; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=WH7VChrDI+e9Uk1fqS2sz7sqWyDarVDdnxdnYZmqXAk=; b=vHTq/U3Id6FrBhLsYrLNIAncwMSC+Auwky48/YfxU80iYDZ/NpKm4Q5X+AK+Mku2Vplu4z 62bOyc4rgBXHnlCEvBRRueCkPtt8DAJJX1x5BBP0bCkaH52L6AjLNpzblJdaKjUfUfLWYW JB1ABBbVTMLdFBEMsLncLOHaQxmQKw0= Received: from suse.cz (unknown [10.100.224.162]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id C5293A3B83; Mon, 1 Nov 2021 10:06:23 +0000 (UTC) Date: Mon, 1 Nov 2021 11:06:23 +0100 From: Petr Mladek To: John Ogness Cc: "chunlei.wang" , Sergey Senozhatsky , Steven Rostedt , Matthias Brugger , linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] printk: ringbuffer: Improve prb_next_seq() performance Message-ID: References: <875ytih3j9.fsf@jogness.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <875ytih3j9.fsf@jogness.linutronix.de> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 2021-10-27 17:54:42, John Ogness wrote: > On 2021-10-27, Petr Mladek wrote: > > diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c > > index 8a7b7362c0dd..24f47fbefbb5 100644 > > --- a/kernel/printk/printk_ringbuffer.c > > +++ b/kernel/printk/printk_ringbuffer.c > > @@ -474,8 +474,10 @@ static enum desc_state desc_read(struct prb_desc_ring *desc_ring, > > * state has been re-checked. A memcpy() for all of @desc > > * cannot be used because of the atomic_t @state_var field. > > */ > > - memcpy(&desc_out->text_blk_lpos, &desc->text_blk_lpos, > > - sizeof(desc_out->text_blk_lpos)); /* LMM(desc_read:C) */ > > + if (desc_out) { > > + memcpy(&desc_out->text_blk_lpos, &desc->text_blk_lpos, > > + sizeof(desc_out->text_blk_lpos)); /* LMM(desc_read:C) */ > > + } > > if (seq_out) > > *seq_out = info->seq; /* also part of desc_read:C */ > > if (caller_id_out) > > You also need this hunk: > > @@ -530,7 +530,8 @@ static enum desc_state desc_read(struct prb_desc_ring *desc_ring, > state_val = atomic_long_read(state_var); /* LMM(desc_read:E) */ > d_state = get_desc_state(id, state_val); > out: > - atomic_long_set(&desc_out->state_var, state_val); > + if (desc_out) > + atomic_long_set(&desc_out->state_var, state_val); > return d_state; > } > > Sorry, I missed it in my last review. This time I build+boot tested the patch. Urgh. Great catch! It seems that my testing was not good enough. Or that I was just lucky. > With this hunk added: > > Reviewed-by: John Ogness I am going to queue it for 5.17 after the pull request for 5.16 is accepted. I do not feel comfortable to rush this into 5.16, especially after finding the bug. The merge window has just started... Anyway, thanks a lot for review and catching the mistake. Best Regards, Petr