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 B7E9DC761AF for ; Wed, 22 Mar 2023 09:16:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230021AbjCVJQd (ORCPT ); Wed, 22 Mar 2023 05:16:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50114 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230040AbjCVJQa (ORCPT ); Wed, 22 Mar 2023 05:16:30 -0400 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3ED6E5BCBC for ; Wed, 22 Mar 2023 02:16:29 -0700 (PDT) Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id EF46E33925; Wed, 22 Mar 2023 09:16:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1679476587; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XE710fYEKcswB5J6E1dCWxswIdz0v6nHSjXnchN4Gj8=; b=LrZG1I0XHUtH1qcWUzbG1QDdcWEjVFNOyr2gCFPAmcCl55wKwDpZX2lkum1IXuq/bsMtk0 oXohYQakD4TfmAXfwOLWGr0dghGRvesCE0aGuLXS1INIzdJpRpS/vTLbsxxoSqGurPMgk5 q7/qli1tIcR4BY5DDCLlRrov+z76jsw= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1679476587; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XE710fYEKcswB5J6E1dCWxswIdz0v6nHSjXnchN4Gj8=; b=hLNAqJpza2k2pWnvQLRU29P5a9DDqQjlIQTk7qd3mANKiNFpzl9kNHQ2xRx2WGTC6uYhcx l/AnOzewWkfw4DCg== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id C5F8113416; Wed, 22 Mar 2023 09:16:27 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id ugSKL2vHGmRwXgAAMHmgww (envelope-from ); Wed, 22 Mar 2023 09:16:27 +0000 Message-ID: <08b98b4a-c6cf-b1b7-a4f8-2ebf3c3a0c67@suse.cz> Date: Wed, 22 Mar 2023 10:16:27 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH v2 3/4] mm/mmap/vma_merge: extend invariants, avoid invalid res, vma Content-Language: en-US To: Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton Cc: David Hildenbrand , Matthew Wilcox , "Liam R . Howlett" , maple-tree@lists.infradead.org, Vernon Yang References: <17b6fc3edc46c4b33aa93b9ef17a63a3a76f4b5f.1679431180.git.lstoakes@gmail.com> From: Vlastimil Babka In-Reply-To: <17b6fc3edc46c4b33aa93b9ef17a63a3a76f4b5f.1679431180.git.lstoakes@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/21/23 21:45, Lorenzo Stoakes wrote: > Previously, vma was an uninitialised variable which was only definitely > assigned as a result of the logic covering all possible input cases - for > it to have remained uninitialised, prev would have to be NULL, and next > would _have_ to be mergeable. > > We now reuse vma to assign curr and next, so to be absolutely explicit, > ensure this variable is _always_ assigned, and while we're at it remove the > redundant assignment of both res and vma (if prev is NULL then we simply > assign to NULL). > > In addition, we absolutely do rely on addr == curr->vm_start should curr > exist, so assert as much. > > Signed-off-by: Lorenzo Stoakes Reviewed-by: Vlastimil Babka Nit suggestion below. > --- > mm/mmap.c | 19 ++++++++++++++----- > 1 file changed, 14 insertions(+), 5 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 6361baf75601..7aec49c3bc74 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -911,7 +911,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, > { > pgoff_t pglen = (end - addr) >> PAGE_SHIFT; > pgoff_t vma_pgoff; > - struct vm_area_struct *curr, *next, *res = NULL; > + struct vm_area_struct *curr, *next, *res; > struct vm_area_struct *vma, *adjust, *remove, *remove2; > int err = -1; > bool merge_prev = false; > @@ -940,14 +940,18 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, > /* Is there a VMA next to a hole (case 1 - 3) or prev (4)? */ > next = vma_lookup(mm, end); > > - /* verify some invariant that must be enforced by the caller */ > + /* > + * By default, we return prev. Cases 3, 4, 8 will instead return next > + * and cases 3, 8 will also update vma to point at next. > + */ > + res = vma = prev; Later in the function there's a line: remove = remove2 = adjust = NULL; Now it would make sense to move it up here? > + > + /* Verify some invariant that must be enforced by the caller. */ > VM_WARN_ON(prev && addr <= prev->vm_start); > - VM_WARN_ON(curr && end > curr->vm_end); > + VM_WARN_ON(curr && (addr != curr->vm_start || end > curr->vm_end)); > VM_WARN_ON(addr >= end); > > if (prev) { > - res = prev; > - vma = prev; > vma_start = prev->vm_start; > vma_pgoff = prev->vm_pgoff; > /* Can we merge the predecessor? */ > @@ -958,6 +962,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, > vma_prev(vmi); > } > } > + > /* Can we merge the successor? */ > if (next && mpol_equal(policy, vma_policy(next)) && > can_vma_merge_before(next, vm_flags, > @@ -998,6 +1003,10 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, > adj_start = -(prev->vm_end - addr); > err = dup_anon_vma(next, prev); > } else { > + /* > + * Note that cases 3 and 8 are the ONLY ones where prev > + * is permitted to be (but is not necessarily) NULL. > + */ > vma = next; /* case 3 */ > vma_start = addr; > vma_end = next->vm_end;