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 X-Spam-Level: X-Spam-Status: No, score=-9.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 26A76C433E2 for ; Fri, 10 Jul 2020 16:25:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0136D206F4 for ; Fri, 10 Jul 2020 16:25:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=bgdev-pl.20150623.gappssmtp.com header.i=@bgdev-pl.20150623.gappssmtp.com header.b="hobbJLEq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728220AbgGJQZC (ORCPT ); Fri, 10 Jul 2020 12:25:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33622 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728156AbgGJQZC (ORCPT ); Fri, 10 Jul 2020 12:25:02 -0400 Received: from mail-il1-x141.google.com (mail-il1-x141.google.com [IPv6:2607:f8b0:4864:20::141]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EC878C08C5DD for ; Fri, 10 Jul 2020 09:25:01 -0700 (PDT) Received: by mail-il1-x141.google.com with SMTP id r12so5568612ilh.4 for ; Fri, 10 Jul 2020 09:25:01 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bgdev-pl.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=H7XPdCmgMImqZF5JZngrO4+1byShoBQA2GaG6Zy8eaQ=; b=hobbJLEqmM+wICRtCGxo8FSciKrE87YjCY5bfIUhTss0vkvgGWa+D+W96pQg9tNjrk JuNjLXEhmjktE4CmN/yuM7qa2QoMD6HKRBB4viJeUCZxI9GJtZs/QuPlw+XZ2Ng8/XKu 8yiHkY90GhRsU/J1avCZ6B6ly27LYnl/fVFG8A404lZ2uB5K5oREfCmsZaXnOMVED+an O6/GiT0Vyxn4ja3ox5HA8S5l24/2WmtnB/9zIcM7kvN+tT5bS8RVQfKxXeugk6V3l6zx lkH+zAhVf3W7YdCv0MeR6Ia7W7wuYJ9jjiBVDNDm7KJSBcxL1ieYnKSpJm/vd1p7U858 /+0w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=H7XPdCmgMImqZF5JZngrO4+1byShoBQA2GaG6Zy8eaQ=; b=M7yPnrUCZvDItYxbGXUIKKF2l3gxfvFP36d2MK92zkOEN++BFKh4IOClcOmflQ6lEW jEECRQyNNvthJkNDKN3bSzkqTO8OMUZMUV9ZJ1tWhGrEz62Q8M8bhw2bEUd3S/VSMd+M WMZ3c3RGquuqPHVZJT3JqDS2tXVC+Suyr/n1VJTCRCKwdDqcolbpcZhponJlRKb6bwAL SOGdIwpdiD0NcodMO/CBPANIWVpXVGBmeGl6HYMJh/gVZpsaiLB1b7D7msOE0v0kxZ8M QueHe8EPyaOrhImaI+xeL3DDVR3HmoVgp6LSPBf21hGXbgG21As416ZvwtcUOfaF/blT IMxQ== X-Gm-Message-State: AOAM531M0KQKlJyETGah1kgQovY4Fy/usm6BID8tT+n2vkNfMew7tuRM JjsqtsmCxx2d3TqS/62inI75r+e2BQ5wBB+f2sZ2zg== X-Google-Smtp-Source: ABdhPJzmLRXRa132tJNdcpdJ4Dy0Mb5/hs/BvJA3zvV0lcrgQHupJU92RI4frdEdYqeKnxmpOFkBkaI7MpLUlGHuja0= X-Received: by 2002:a92:c00a:: with SMTP id q10mr29286029ild.220.1594398301007; Fri, 10 Jul 2020 09:25:01 -0700 (PDT) MIME-Version: 1.0 References: <20200629065008.27620-1-brgl@bgdev.pl> <20200629065008.27620-5-brgl@bgdev.pl> <5c2e7514-b6d0-1331-37b0-d17a0cdb9693@nvidia.com> <9cd4521b-aba0-616b-8957-8f21b9ba3068@nvidia.com> In-Reply-To: <9cd4521b-aba0-616b-8957-8f21b9ba3068@nvidia.com> From: Bartosz Golaszewski Date: Fri, 10 Jul 2020 18:24:50 +0200 Message-ID: Subject: Re: [PATCH v2 4/6] devres: handle zero size in devm_kmalloc() To: Jon Hunter Cc: Jonathan Corbet , Greg Kroah-Hartman , "Rafael J . Wysocki" , Guenter Roeck , Jean Delvare , linux-doc , Linux Kernel Mailing List , linux-hwmon@vger.kernel.org, Bartosz Golaszewski Content-Type: text/plain; charset="UTF-8" Sender: linux-hwmon-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-hwmon@vger.kernel.org On Fri, Jul 10, 2020 at 6:11 PM Jon Hunter wrote: > > > On 10/07/2020 17:03, Bartosz Golaszewski wrote: > > On Fri, Jul 10, 2020 at 3:46 PM Jon Hunter wrote: > >> > >> Hi Bartosz, > >> > >> On 29/06/2020 07:50, Bartosz Golaszewski wrote: > >>> From: Bartosz Golaszewski > >>> > >>> Make devm_kmalloc() behave similarly to non-managed kmalloc(): return > >>> ZERO_SIZE_PTR when requested size is 0. Update devm_kfree() to handle > >>> this case. > >>> > >>> Signed-off-by: Bartosz Golaszewski > >>> --- > >>> drivers/base/devres.c | 9 ++++++--- > >>> 1 file changed, 6 insertions(+), 3 deletions(-) > >>> > >>> diff --git a/drivers/base/devres.c b/drivers/base/devres.c > >>> index 1df1fb10b2d9..ed615d3b9cf1 100644 > >>> --- a/drivers/base/devres.c > >>> +++ b/drivers/base/devres.c > >>> @@ -819,6 +819,9 @@ void *devm_kmalloc(struct device *dev, size_t size, gfp_t gfp) > >>> { > >>> struct devres *dr; > >>> > >>> + if (unlikely(!size)) > >>> + return ZERO_SIZE_PTR; > >>> + > >>> /* use raw alloc_dr for kmalloc caller tracing */ > >>> dr = alloc_dr(devm_kmalloc_release, size, gfp, dev_to_node(dev)); > >>> if (unlikely(!dr)) > >>> @@ -950,10 +953,10 @@ void devm_kfree(struct device *dev, const void *p) > >>> int rc; > >>> > >>> /* > >>> - * Special case: pointer to a string in .rodata returned by > >>> - * devm_kstrdup_const(). > >>> + * Special cases: pointer to a string in .rodata returned by > >>> + * devm_kstrdup_const() or NULL/ZERO ptr. > >>> */ > >>> - if (unlikely(is_kernel_rodata((unsigned long)p))) > >>> + if (unlikely(is_kernel_rodata((unsigned long)p) || ZERO_OR_NULL_PTR(p))) > >>> return; > >>> > >>> rc = devres_destroy(dev, devm_kmalloc_release, > >> > >> > >> This change caught a bug in one of our Tegra drivers, which I am in the > >> process of fixing. Once I bisected to this commit it was easy to track > >> down, but I am wondering if there is any reason why we don't add a > >> WARN_ON() if size is 0 in devm_kmalloc? It was essentially what I ended > >> up doing to find the bug. > >> > >> Jon > >> > >> -- > >> nvpublic > > > > Hi Jon, > > > > this is in line with what the regular kmalloc() does. If size is zero, > > it returns ZERO_SIZE_PTR. It's not an error condition. Actually in > > user-space malloc() does a similar thing: for size == 0 it allocates > > one-byte and returns a pointer to it (at least in glibc). > > > Yes that's fine, I was just wondering if there is any reason not to WARN > as well? > > Cheers > Jon > Why? Nothing bad happens. Regular kmalloc() doesn't warn, why should devm_kmalloc() do? Bartosz