From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DC1952D73B0 for ; Fri, 3 Oct 2025 17:05:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759511117; cv=none; b=sZOwYNZc0hU/PAw4gTeo/9IkgMnsWv1Zb1k0x/jMNGZlQPWZo/sbReXLK8E6KlWN0bXX+vUd+xIJt/mK6ur3hjhU1/jozTVoYkq0eRMsU6ypNyAFEjR37FCRr7LfhoPaVanCaBwhsGswzklbhQ/7V0FDBdnkskI5jhvh+w8wuV8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759511117; c=relaxed/simple; bh=dCKrt8dplsaCnu926SB7MnYRZ15xSlDKLeikRK7Sik8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=VapgcX4uM4AbMuJC0msvW5sYTItWgwngJkTZsgkFYw56hwgsSvgxzQmRFVFtbagflExCRmj1Hlwmsr82aPUtj6I4OpPMOZrs3XWOMgszNSiVWe5yf/T0cn9b/se2DzGmOvh4WQKLSqUOZAyi7pnelaLKx27VCtYdB1ugnyEyoNk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 17081C4CEF5; Fri, 3 Oct 2025 17:05:15 +0000 (UTC) Date: Fri, 3 Oct 2025 18:05:13 +0100 From: Catalin Marinas To: syzbot Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, will@kernel.org, David Hildenbrand Subject: Re: [syzbot] [arm?] WARNING in copy_highpage Message-ID: References: <68dda1ae.a00a0220.102ee.0065.GAE@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <68dda1ae.a00a0220.102ee.0065.GAE@google.com> Thanks for the report (for some reason, outlook did not deliver this to my inbox; Will pointed me at the message) Adding David H as well, he may have some ideas. I haven't tried to reproduce it yet. On Wed, Oct 01, 2025 at 02:48:30PM -0700, syzbot wrote: > syzbot found the following issue on: > > HEAD commit: fec734e8d564 Merge tag 'riscv-for-linus-v6.17-rc8' of git:.. So that's just before 6.17, not something that turned up during the merging window. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=12187d34580000 > kernel config: https://syzkaller.appspot.com/x/.config?x=13bd892ec3b155a2 > dashboard link: https://syzkaller.appspot.com/bug?extid=d1974fc28545a3e6218b > compiler: aarch64-linux-gnu-gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40 > userspace arch: arm64 > > Unfortunately, I don't have any reproducer for this issue yet. > > Downloadable assets: > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/fa3fbcfdac58/non_bootable_disk-fec734e8.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/d7e18b408aea/vmlinux-fec734e8.xz > kernel image: https://storage.googleapis.com/syzbot-assets/9b7984f47117/Image-fec734e8.gz.xz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+d1974fc28545a3e6218b@syzkaller.appspotmail.com > > ------------[ cut here ]------------ > WARNING: CPU: 1 PID: 25189 at arch/arm64/mm/copypage.c:55 try_page_mte_tagging arch/arm64/include/asm/mte.h:93 [inline] > WARNING: CPU: 1 PID: 25189 at arch/arm64/mm/copypage.c:55 copy_highpage+0x150/0x334 arch/arm64/mm/copypage.c:55 This warning means that the destination page is already tagged (PG_mte_tagged set) when it got to copy_page(). In general it is fine as we copy into and override all the tags but my assumption until now has been that such new pages are always untagged. > Modules linked in: > CPU: 1 UID: 0 PID: 25189 Comm: syz.2.7336 Not tainted syzkaller #0 PREEMPT > Hardware name: linux,dummy-virt (DT) > pstate: 00402009 (nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) > pc : copy_highpage+0x150/0x334 arch/arm64/mm/copypage.c:55 > lr : copy_highpage+0xb4/0x334 arch/arm64/mm/copypage.c:25 > sp : ffff800088053940 > x29: ffff800088053940 x28: ffffc1ffc0acf800 x27: ffff800088053b10 > x26: ffffc1ffc0acf808 x25: ffffc1ffc037b1c0 x24: ffffc1ffc037b1c0 > x23: ffffc1ffc0acf800 x22: ffffc1ffc0acf800 x21: fff000002b3e0000 > x20: fff000000dec7000 x19: ffffc1ffc037b1c0 x18: 0000000000000000 > x17: fff07ffffcffa000 x16: ffff800080008000 x15: 0000000000000001 > x14: 0000000000000000 x13: 0000000000000003 x12: 000000000006d9ad > x11: 0000000000000000 x10: 0000000000000010 x9 : 0000000000000000 > x8 : 0000000000000000 x7 : 0000000000000000 x6 : 0000000000000000 > x5 : ffff800088053b18 x4 : ffff80008032df94 x3 : 00000000ff000000 > x2 : 01ffc00003000001 x1 : 01ffc00003000001 x0 : 01ffc00003000001 > Call trace: > try_page_mte_tagging arch/arm64/include/asm/mte.h:93 [inline] (P) > copy_highpage+0x150/0x334 arch/arm64/mm/copypage.c:55 (P) > copy_mc_highpage include/linux/highmem.h:383 [inline] > folio_mc_copy+0x44/0x6c mm/util.c:740 > __migrate_folio.constprop.0+0xc4/0x23c mm/migrate.c:851 > migrate_folio+0x1c/0x2c mm/migrate.c:882 > move_to_new_folio+0x58/0x144 mm/migrate.c:1097 > migrate_folio_move mm/migrate.c:1370 [inline] > migrate_folios_move mm/migrate.c:1719 [inline] > migrate_pages_batch+0xaf4/0x1024 mm/migrate.c:1966 > migrate_pages_sync mm/migrate.c:2023 [inline] > migrate_pages+0xb9c/0xcdc mm/migrate.c:2105 > do_mbind+0x20c/0x4a4 mm/mempolicy.c:1539 > kernel_mbind mm/mempolicy.c:1682 [inline] > __do_sys_mbind mm/mempolicy.c:1756 [inline] I don't think we ever stressed MTE with mbind before. I have a suspicion this problem has been around for some time. My reading of do_mbind() is that it ends up allocating pages for migrating into via alloc_migration_target_by_mpol() -> folio_alloc_mpol(). Pages returned should be untagged and uninitialised unless the PG_* flags have not been cleared on a prior free. Or migrate_pages_batch() somehow reuses some pages instead of reallocating. -- Catalin