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 C8E93C433EF for ; Fri, 22 Apr 2022 07:35:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1444900AbiDVHh5 (ORCPT ); Fri, 22 Apr 2022 03:37:57 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52056 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1444876AbiDVHhy (ORCPT ); Fri, 22 Apr 2022 03:37:54 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D9AA1260F; Fri, 22 Apr 2022 00:35:00 -0700 (PDT) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 9226E210F4; Fri, 22 Apr 2022 07:34:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1650612899; 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=CoKlO+fXUiau8VMVUQKx3k/6EuFzG9GIbfxFrogHx6w=; b=dySGsqJdEmSJDYmSvOklfVpkuZHJ23u9g1XhRJDcQoLdKgRG5kmI1lpiTUWcSy7MtqR7zM kXwCyLTlbnp+iE9neiu8jg1lhFPIDng+OjhqwbJ52cuWGbwwYU1o5p6p+n2i/KC3xGvKZl 0hE/7gJMEJKlgdQaF4sMg91/V0j/qiM= Received: from suse.cz (unknown [10.100.201.86]) (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 6010B2C146; Fri, 22 Apr 2022 07:34:59 +0000 (UTC) Date: Fri, 22 Apr 2022 09:34:57 +0200 From: Michal Hocko To: Christophe JAILLET Cc: Greg Kroah-Hartman , "Rafael J. Wysocki" , Scott Cheloha , Andrew Morton , Nathan Lynch , David Hildenbrand , linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org Subject: Re: [PATCH] drivers/base/memory: Fix a reference counting issue in __add_memory_block() Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 22-04-22 09:15:21, Christophe JAILLET wrote: > There is no point in doing put_device()/device_unregister() on a > device that has just been registered a few lines above. This will lead to > a double reference decrement. This is a bit confusing. I would rephrase. " __add_memory_block calls both put_device and device_unregister when storing the memory block into the xarray. This is incorrect because xarray doesn't take an additional reference and device_unregister already calls put_device. " Btw. I do not think this failure path can be triggered, or is there a way to hit it? > I guess that this put_device()/device_unregister() is a cut'n'paste from > remove_memory_block() (i.e. unregister_memory() at the time being) which > does need it. > > Fixes: 4fb6eabf1037 ("drivers/base/memory.c: cache memory blocks in xarray to accelerate lookup") > Signed-off-by: Christophe JAILLET Other than that looks good to me. With the changelog clarified, especially the part that evaluates whether this is a real or a theoretical problem, feel free to add Acked-by: Michal Hocko Thanks! > --- > drivers/base/memory.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/drivers/base/memory.c b/drivers/base/memory.c > index 7222ff9b5e05..084d67fd55cc 100644 > --- a/drivers/base/memory.c > +++ b/drivers/base/memory.c > @@ -636,10 +636,9 @@ static int __add_memory_block(struct memory_block *memory) > } > ret = xa_err(xa_store(&memory_blocks, memory->dev.id, memory, > GFP_KERNEL)); > - if (ret) { > - put_device(&memory->dev); > + if (ret) > device_unregister(&memory->dev); > - } > + > return ret; > } > > -- > 2.32.0 -- Michal Hocko SUSE Labs