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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 65B61F327CA for ; Tue, 21 Apr 2026 09:08:34 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 955806B0088; Tue, 21 Apr 2026 05:08:33 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8DF006B0089; Tue, 21 Apr 2026 05:08:33 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7A6E76B008A; Tue, 21 Apr 2026 05:08:33 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 6389D6B0088 for ; Tue, 21 Apr 2026 05:08:33 -0400 (EDT) Received: from smtpin02.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 0B8BEE5B74 for ; Tue, 21 Apr 2026 09:08:33 +0000 (UTC) X-FDA: 84681987306.02.1582676 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf27.hostedemail.com (Postfix) with ESMTP id 4999940004 for ; Tue, 21 Apr 2026 09:08:31 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=qHrgWQHh; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf27.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1776762511; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=iCBXrhg7C9/srZBYKXkvWBRwmDURbGGY8aIrv/zoQug=; b=sqouVGxgCOS0QrXENmDM+HKrT/bq6AxQB+uiLHx/KXjNgZ65MfzZHqUTnAoWUsgFaCMV5B m7p56sEKHJwCYGE9LTVkBQAbI4Ck/itneclBPT1JcEy2gPajAG9KhkLEw+OkZqfnhhGYB6 9+Jy8VTUxlEG+MQjo2ZS8xTC2mKHo9I= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=qHrgWQHh; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf27.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1776762511; a=rsa-sha256; cv=none; b=yPXbnAUsGO7DTxb/6OdbxcgOACpp8meD94wdjCdMWG9Y+HuxoIxLLRZtxmcurZskEdKTMZ puaYVglsGGT1eQ6qPqCWoUGhHMah0IihLc0LJJRsMbiMBi09tOz+ND5J1Zx4GILNKn8BtN LrD0uVxwIZXS6QYqQrdNqTP7jR1EMHA= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 12BED40B4C; Tue, 21 Apr 2026 09:08:30 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D4575C2BCB5; Tue, 21 Apr 2026 09:08:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776762509; bh=JnjFXHz/DzaxlCC1EjhtvgOWVsZUYZ1qXPlyL5Gg3Mk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=qHrgWQHhOHD+v7BkML+OGgs7w/nKJBfA8bmC5rZq1RqPZcVUc4LkU4Tp2G0Xekbsf T/ngt4IGDVyFGM2c1dXeWNIJzARNeIZZUr3sKEbXj5zohufQJ7YZ0JoSnGqQMzZIAd wQiCG8b3OuEmQyj/3cAEB6wnRhlkQ64luJuEKnHXe1rf6VTjmscUi4+RwtH1qr6Miz M37r41MIXPe7jmsjSbOzCjsqmJHZJ2nR5BEdHqulAHA1Gg3/S99IHJRjrJ5JTwCx0l kVX2E4Z5FhEBG6sMoXScopZXMVgzM5M2UCqUKH36sWcXh6A60qcGA1S01NTwCVQHKT j8308YPwRtrJw== Date: Tue, 21 Apr 2026 10:08:23 +0100 From: Lorenzo Stoakes To: Ye Liu Cc: Andrew Morton , David Hildenbrand , "Liam R. Howlett" , Ye Liu , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kairui Song , Qi Zheng , Shakeel Butt , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Jann Horn , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: handle potential NULL return from anon_vma_name_reuse() Message-ID: References: <20260421085056.26033-1-ye.liu@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260421085056.26033-1-ye.liu@linux.dev> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 4999940004 X-Stat-Signature: mgzwu54raudrbiq7e5u17w7qqmnrwdur X-Rspam-User: X-HE-Tag: 1776762511-561291 X-HE-Meta: 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 kZbN6/ar GYVLpVE2BlXDPA1ICf/n1P7yP5piHzeZ9nnWZrpN5eFKFa3MJRbhNsgZPxFZmQdWPjiHNjnus4TVfpntuMgsvQARuzUcySCG1nIprLC0qPJZxh9HmVdQmAuIGb/ObKAZtU0Hgrf2BMZGsJF9Aj4bQXEE9Jft6/CcTUYxjHsKakQxv5/H43dafc6WtW7HuIKPla8Tg+ku+H4tF2wkPRSjejMEBpF2mCugw53/V6K0bXE9dYrxNq5XTxCmLO68IgwWJ43rTytHdwRsaGYUdY4M6apr+PfmkQXLkP7dSTH+SMitThWA= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: NAK, expected allocation failures (even if practically impossible) should not cause arbitrary kernel warnings. But also this is very silly, you would need INT_MAX references on the anon_name to happen first... On Tue, Apr 21, 2026 at 04:50:55PM +0800, Ye Liu wrote: > From: Ye Liu > > The anon_vma_name_reuse() function may return NULL if memory allocation > fails in anon_vma_name_alloc(). Currently, callers dup_anon_vma_name() > and replace_anon_vma_name() do not check the return value, which could > lead to NULL pointer dereferences. We assign NULL if the allocation failed. And every code path understands vma->anon_vma_name being NULL to be a valid situation of that VMA not having a name. In the case you're failing an allocation that small, the system is under extreme memory pressure. Not propagating an anon_vma_name, which is cosmetic, is totally fine under those circumstances. But also, you'd require the anon_vma_name to be saturated at REFCOUNT_MAX == INT_MAX. So this is just silly. > > This patch adds proper error handling: > - In dup_anon_vma_name(), if anon_vma_name_reuse() returns NULL, emit a > warning via WARN_ON_ONCE(1) since this is an unexpected condition. It's not? Your whole thesis is that allocation failures can happen here and cause a problem, so you can't simultaneously say it's 'unexpected'? > - In replace_anon_vma_name(), return -ENOMEM to propagate the allocation > failure to the caller. > > These changes improve robustness against memory allocation failures. No, they add a bunch of noise, then make an allocation failure into an arbitrary, new kernel warning. > > Signed-off-by: Ye Liu > --- > include/linux/mm_inline.h | 12 +++++++++--- > mm/madvise.c | 7 ++++++- > 2 files changed, 15 insertions(+), 4 deletions(-) > > diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h > index a171070e15f0..9bbaf8287806 100644 > --- a/include/linux/mm_inline.h > +++ b/include/linux/mm_inline.h > @@ -421,9 +421,15 @@ static inline void dup_anon_vma_name(struct vm_area_struct *orig_vma, > struct vm_area_struct *new_vma) > { > struct anon_vma_name *anon_name = anon_vma_name(orig_vma); > - > - if (anon_name) > - new_vma->anon_name = anon_vma_name_reuse(anon_name); > + struct anon_vma_name *new_name; > + > + if (anon_name) { > + new_name = anon_vma_name_reuse(anon_name); > + if (new_name) > + new_vma->anon_name = new_name; > + else > + WARN_ON_ONCE(1); > + } This is horrible code, but as I said above, this is not only wrong it's actively bad - you're causing an allocation failure to result in a kernel warning. We don't mind anon_vma_name not being propagated after billions of references and under maximally extreme memory pressure/fatal signal propagation. > } > > static inline void free_anon_vma_name(struct vm_area_struct *vma) > diff --git a/mm/madvise.c b/mm/madvise.c > index 69708e953cf5..ccb937a37e70 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -118,6 +118,7 @@ static int replace_anon_vma_name(struct vm_area_struct *vma, > struct anon_vma_name *anon_name) > { > struct anon_vma_name *orig_name = anon_vma_name(vma); > + struct anon_vma_name *new_name; > > if (!anon_name) { > vma->anon_name = NULL; > @@ -128,7 +129,11 @@ static int replace_anon_vma_name(struct vm_area_struct *vma, > if (anon_vma_name_eq(orig_name, anon_name)) > return 0; > > - vma->anon_name = anon_vma_name_reuse(anon_name); > + new_name = anon_vma_name_reuse(anon_name); > + if (!new_name) > + return -ENOMEM; > + > + vma->anon_name = new_name; This is pointless noise. Billions of references, extreme memory pressure (practically impossible anyway). > anon_vma_name_put(orig_name); > > return 0; > -- > 2.43.0 > Thanks, Lorenzo