From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 D0A1C1CA84; Mon, 23 Sep 2024 19:57:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727121471; cv=none; b=DncUnhu8AnPCfR5vkMXRRkrmCL6Ujf+7CWp7EwpCPlUWyzUNFjphRDAfPKDwueyasYYccqQZvMRGwqYbCG5PqUTdH7xo578zYe7549ApKe/sSQUfiB3OAQplv3Rh7xbLuEJZZx9eBzwWP341Gie82U1YABLJz0i+5lAUgO1NR9c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727121471; c=relaxed/simple; bh=j3GLpyNYImX/2q/swXZVeynGwkFbrkAuEiTemEHwQfY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Iv7zn1NmRNVi56oi1ad6wZyuOtQ/vDcMzibgKRXmf6DTcpqDmP/jKo5Yr+ZecyMaI52Jff3l7mOVfa2pm8svbReTGLU0EMb3HVIgZAfRVhSpSg7F7BLNHvYx8rYUM49VAU85jspcQOlxh32lNuDJyNQBkzCb2S//XdoyFlQez5M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=eA0VMEbQ; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="eA0VMEbQ" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=XVNIglgCnWlcmQeWjuludc9gerVDM3DtscyXtyevQA0=; b=eA0VMEbQv8Vvzhas7owyR9f0xB IUJVLeEU3befr/ZRhRs/Udxp1DkOmE24hGCK0FIXDFGqOIgs1TNiUSopHQXYc7BfEc0gYkG8Oyyxu 3QFeE45ki5oa8ERVOLe7Z4bJ9SRKFYGD7ImywD1/BzajFU2LuPwbMqHzUQ4ASO4RlaGKqE1tjwdlr qCJWl0p8P7KWOkSinAKMpU4gztoIrwI4qwytpm4nGQlYfE7tCVQPmg74LfpR6a0ot85vXuqMViTlX 8NWDM08ZSRnlxZgmOYiQhi3dUbg4lFjApyFUKnTtUH8laP8gq90JErScf/2W4McmFCcFLB3oVXQcj okDBN9Ww==; Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1sspBb-0000000GstZ-16he; Mon, 23 Sep 2024 19:57:31 +0000 Date: Mon, 23 Sep 2024 20:57:31 +0100 From: Matthew Wilcox To: David Hildenbrand Cc: Jeongjun Park , akpm@linux-foundation.org, wangkefeng.wang@huawei.com, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, syzbot Subject: Re: [PATCH] mm: migrate: fix data-race in migrate_folio_unmap() Message-ID: References: <20240922151708.33949-1-aha310510@gmail.com> <31e90b74-8bd1-4bfe-9384-8d479735d2be@redhat.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: <31e90b74-8bd1-4bfe-9384-8d479735d2be@redhat.com> On Mon, Sep 23, 2024 at 05:56:40PM +0200, David Hildenbrand wrote: > On 22.09.24 17:17, Jeongjun Park wrote: > > I found a report from syzbot [1] > > > > When __folio_test_movable() is called in migrate_folio_unmap() to read > > folio->mapping, a data race occurs because the folio is read without > > protecting it with folio_lock. > > > > This can cause unintended behavior because folio->mapping is initialized > > to a NULL value. Therefore, I think it is appropriate to call > > __folio_test_movable() under the protection of folio_lock to prevent > > data-race. > > We hold a folio reference, would we really see PAGE_MAPPING_MOVABLE flip? > Hmm No; this shows a page cache folio getting truncated. It's fine; really a false alarm from the tool. I don't think the proposed patch introduces any problems, but it's all a bit meh. > Even a racing __ClearPageMovable() would still leave PAGE_MAPPING_MOVABLE > set. > > > [1] > > > > ================================================================== > > BUG: KCSAN: data-race in __filemap_remove_folio / migrate_pages_batch > > > > write to 0xffffea0004b81dd8 of 8 bytes by task 6348 on cpu 0: > > page_cache_delete mm/filemap.c:153 [inline] > > __filemap_remove_folio+0x1ac/0x2c0 mm/filemap.c:233 > > filemap_remove_folio+0x6b/0x1f0 mm/filemap.c:265 > > truncate_inode_folio+0x42/0x50 mm/truncate.c:178 > > shmem_undo_range+0x25b/0xa70 mm/shmem.c:1028 > > shmem_truncate_range mm/shmem.c:1144 [inline] > > shmem_evict_inode+0x14d/0x530 mm/shmem.c:1272 > > evict+0x2f0/0x580 fs/inode.c:731 > > iput_final fs/inode.c:1883 [inline] > > iput+0x42a/0x5b0 fs/inode.c:1909 > > dentry_unlink_inode+0x24f/0x260 fs/dcache.c:412 > > __dentry_kill+0x18b/0x4c0 fs/dcache.c:615 > > dput+0x5c/0xd0 fs/dcache.c:857 > > __fput+0x3fb/0x6d0 fs/file_table.c:439 > > ____fput+0x1c/0x30 fs/file_table.c:459 > > task_work_run+0x13a/0x1a0 kernel/task_work.c:228 > > resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] > > exit_to_user_mode_loop kernel/entry/common.c:114 [inline] > > exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline] > > __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline] > > syscall_exit_to_user_mode+0xbe/0x130 kernel/entry/common.c:218 > > do_syscall_64+0xd6/0x1c0 arch/x86/entry/common.c:89 > > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > > > read to 0xffffea0004b81dd8 of 8 bytes by task 6342 on cpu 1: > > __folio_test_movable include/linux/page-flags.h:699 [inline] > > migrate_folio_unmap mm/migrate.c:1199 [inline] > > migrate_pages_batch+0x24c/0x1940 mm/migrate.c:1797 > > migrate_pages_sync mm/migrate.c:1963 [inline] > > migrate_pages+0xff1/0x1820 mm/migrate.c:2072 > > do_mbind mm/mempolicy.c:1390 [inline] > > kernel_mbind mm/mempolicy.c:1533 [inline] > > __do_sys_mbind mm/mempolicy.c:1607 [inline] > > __se_sys_mbind+0xf76/0x1160 mm/mempolicy.c:1603 > > __x64_sys_mbind+0x78/0x90 mm/mempolicy.c:1603 > > x64_sys_call+0x2b4d/0x2d60 arch/x86/include/generated/asm/syscalls_64.h:238 > > do_syscall_x64 arch/x86/entry/common.c:52 [inline] > > do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83 > > entry_SYSCALL_64_after_hwframe+0x77/0x7f > > > > value changed: 0xffff888127601078 -> 0x0000000000000000 > > Note that this doesn't flip PAGE_MAPPING_MOVABLE, just some unrelated bits. > > > > > Reported-by: syzbot > > Cc: stable@vger.kernel.org > > Fixes: 7e2a5e5ab217 ("mm: migrate: use __folio_test_movable()") > > Signed-off-by: Jeongjun Park > > --- > > mm/migrate.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/mm/migrate.c b/mm/migrate.c > > index 923ea80ba744..e62dac12406b 100644 > > --- a/mm/migrate.c > > +++ b/mm/migrate.c > > @@ -1118,7 +1118,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio, > > int rc = -EAGAIN; > > int old_page_state = 0; > > struct anon_vma *anon_vma = NULL; > > - bool is_lru = !__folio_test_movable(src); > > + bool is_lru; > > bool locked = false; > > bool dst_locked = false; > > @@ -1172,6 +1172,7 @@ static int migrate_folio_unmap(new_folio_t get_new_folio, > > locked = true; > > if (folio_test_mlocked(src)) > > old_page_state |= PAGE_WAS_MLOCKED; > > + is_lru = !__folio_test_movable(src); > > > Looks straight forward, though > > Acked-by: David Hildenbrand > > > -- > Cheers, > > David / dhildenb >