From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792739777; b=NhFXbseEf3sfC070/noIpEq5UE6Q0gkvCWwJL19P51dleU3ohStV0mJGvlJS68v2Vs5h 3+XGrhxSVCLVWjeweFXwdqg0ErT1cNyR7VxUWEm4TxlIxi2rhQ42PzXvPkUFTCK/64BG/ yobLY7YJeyOiMhvWNmMytYjUYNB0x1YREU6XnBR3uZG6/86u7FUiUR+J5DVPLvbhUljkn WxYfQ42cu+ZiIDqIgLzmuVM6o9RHvtOWdUx8j9ASjRzEn+DO6RWlnwW8dAIN4yxVJHPbD YyLdywoizliGATChsXx5RlImWfZuldQu01fWyVsoBFADCCCMKPqfal8gFjwZNQGGmRQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792739777; h=Received:DKIM-Signature:Message-ID:Date:MIME-Version:User-Agent: Subject:To:Cc:References:From:Content-Language:Autocrypt:In-Reply-To: Content-Type:Content-Transfer-Encoding; bh=pkqrD//fnGQ72hjouszMioilp+NszrPnGIYWVd5G9RA=; b=pSGxoNQQgXU/zfTmHL1M/4tOjPjAEhlTbF4ErMQ84W2igM/w8wUzXl8s/pD+OP4b30AM ABNmJ0sbFNQs1Dhqb4ICm0KTGvEEHIJ17v/OInOvo2YnncCy7ieLa91eSYLEfoXvbSdNe aWV2jW8MCcSSUCLqFH3pCh/LCaF0E0zXp8k8p4PW/FDrRo2Q7l5phBEbd2InfUCEYa8/t OWGqMX48/LMwfcIlWbAuaG4NmnF+3wwxGzby4yDziVSrSkhh98Ryi0SKwZhmt5Bo627Kf 29A4G10I89qW55nNiqKkRelpA3NM0RZbW1VbD2mTYVQWtNGklJ961mtUyxMZqzLmohQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=G285uqat; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 07453606A31E for ; Fri, 23 Oct 2026 07:16:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=G285uqat Received: by smtp.kernel.org (Postfix) with ESMTPSA id A7F771F01825; Fri, 23 Oct 2026 07:16:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792739776; bh=pkqrD//fnGQ72hjouszMioilp+NszrPnGIYWVd5G9RA=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=G285uqatlfpZ6ocauqOB0OLsQ70I1Dgw7gK2NxUGwd/MJRYS7Y6vqNl+H7gQbGOcK ftTeh0DVX4xAqez6LW/Vht3wP+DRN48+3dv2nf50i8NnbwNXWGOp2NWv7uMAtIwl/B wn131MQ1wIWH1p4Fxfow5ose0tQU+YmBccoXuePJXI4+LieWBCayhLnw/BIreTaCcf SGriwCo3bcjVU9kJmUHE7nBCVWx0ouoPkS0fHzvpWNGjMVD5RsT83KGen5F+L1fzOA Skf1aCe4gwU8hoEyy1eTHSXTX0MTUtX/eDuHaHy8C+I0b8AklN7DahVTc92e5aUbi5 tIKR+bgmltb0w== Message-ID: <8c53e58c-f7d2-4e98-8d03-7ff1163c1159@kernel.org> Date: Fri, 23 Oct 2026 09:16:12 +0200 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [REGRESSION] mremap() fails VMA expansion when VM_MIXEDMAP is set To: Luiz Capitulino , Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes Cc: Jann Horn , Pedro Falcato , David Hildenbrand , Jakub Matena , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20261023023106.515365-1-luizcap@redhat.com> From: "Vlastimil Babka (SUSE)" Content-Language: en-US Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <20261023023106.515365-1-luizcap@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/23/26 04:31, Luiz Capitulino wrote: > Growing a VM_MIXEDMAP VMA with mremap(), with or without MREMAP_MAYMOVE, fails > with -ENOMEM when the address range after the VMA is free. > > This regression was introduced in v6.1 by commit ca3d76b0aa80 ("mm: add merging > after mremap resize"). This commit changed mremap() to use vma_merge() instead > of vma_adjust() for the expansion case. However, vma_merge() returns NULL for > a VMA that has any of the VM_SPECIAL flags set. Hi, 6.1 was a rather long time ago. How was it discovered just now? I.e. what use case broke by the change and prompted creating the reproducer? Thanks, Vlastimil > The issue is also present in latest Linus tree, except that the code has been > refactored. In the current tree, the path now is expand_vma_in_place() -> > vma_merge_extend() -> vma_merge_new_range(), which performs the check: > > /* Special VMAs are unmergeable, also if no prev/next. */ > if (vma_flags_test_any_mask(&vmg->vma_flags, VMA_SPECIAL_FLAGS) || > (!prev && !next)) > return NULL; > > This issue was originally reproduced with an external module that sets > VM_MIXEDMAP on a VMA because it wants to insert pages with vm_insert_page(). > However, there's at least one in-tree reproducer: tcp_mmap(). > > Note that commit ca3d76b0aa80 introduced other VMA expansion regressions, > but they were caught and fixed early: > > - 6f12be792fde ("mm, mremap: fix mremap() expanding vma with addr inside vma") > - d014cd7c1c35 ("mm, mremap: fix mremap() expanding for vma's with vm_ops->close()") > > Below you'll find a reproducer and an attempted fix. > > Reproducer > ========== > > This reproducer was written by an LLM and uses tcp_mmap(). It reproduces > against v6.1 and latest Linus tree (2a08195e4db5). The issue is not > reproduced on v6.0. > > #define _GNU_SOURCE > #include > #include > #include > #include > #include > > int main(void) > { > int fd, pagesize; > void *p, *ret; > > fd = socket(AF_INET, SOCK_STREAM, 0); > if (fd < 0) { > perror("socket"); > return 1; > } > > pagesize = getpagesize(); > > /* tcp_mmap() sets VM_MIXEDMAP on this vma. */ > p = mmap(NULL, 2 * pagesize, PROT_READ, MAP_SHARED, fd, 0); > if (p == MAP_FAILED) { > perror("mmap"); > return 1; > } > > /* Drop the upper half, so growing back into it can happen in place. */ > if (munmap((char *)p + pagesize, pagesize)) { > perror("munmap"); > return 1; > } > > errno = 0; > ret = mremap(p, pagesize, 2 * pagesize, MREMAP_MAYMOVE); > if (ret == MAP_FAILED) { > printf("BUG REPRODUCED errno=%d\n", errno); > return 1; > } > > printf("NOT REPRODUCED\n"); > > return 0; > } > > Sketch fix > ========== > > In the fix below, I started with the same idea as d014cd7c1c35: on v6.1 I > made mremap() expand VM_MIXEDMAP VMAs the same way that commit did for > VMAs with vm_ops->close(). Then I adapted it to the current tree. It fixes > the reproducer and I didn't get regressions in MM kselftests nor the > tools/testing/vma test. > > However, I'm not posting this as a fix because I'm unfamiliar with the VMA > code so I'm not confident this is the right approach. > > I really don't mind someone more familiar with the code taking this over. > > diff --git a/mm/vma.c b/mm/vma.c > index 6c35f0d775ab..ac9a0a8a4be9 100644 > --- a/mm/vma.c > +++ b/mm/vma.c > @@ -851,9 +851,15 @@ static int commit_merge(struct vma_merge_struct *vmg) > return 0; > } > > -/* We can only remove VMAs when merging if they do not have a close hook. */ > static bool can_merge_remove_vma(struct vm_area_struct *vma) > { > + if (vma_flags_test(&vma->flags, VMA_MIXEDMAP_BIT)) > + return false; > + > + /* > + * We can only remove VMAs when merging if they do not have a > + * close hook. > + */ > return !vma->vm_ops || !vma->vm_ops->close; > } > > @@ -1093,6 +1099,20 @@ static __must_check struct vm_area_struct *vma_merge_existing_range( > return NULL; > } > > +static bool can_merge_vma(const struct vma_merge_struct *vmg) > +{ > + /* VMAs without prev/next are unmergeable */ > + if (!vmg->prev && !vmg->next) > + return false; > + > + /* We can't merge VMA_IO, VMA_DONTEXPAND or VMA_PFNMAP */ > + if (vma_flags_test_any(&vmg->vma_flags, VMA_IO_BIT, VMA_DONTEXPAND_BIT, > + VMA_PFNMAP_BIT)) > + return false; > + > + return true; > +} > + > /* > * vma_merge_new_range - Attempt to merge a new VMA into address space > * > @@ -1152,9 +1172,7 @@ struct vm_area_struct *vma_merge_new_range(struct vma_merge_struct *vmg) > > vmg->state = VMA_MERGE_NOMERGE; > > - /* Special VMAs are unmergeable, also if no prev/next. */ > - if (vma_flags_test_any_mask(&vmg->vma_flags, VMA_SPECIAL_FLAGS) || > - (!prev && !next)) > + if (!can_merge_vma(vmg)) > return NULL; > > can_merge_left = can_vma_merge_left(vmg); >