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 0D08B50094E for ; Fri, 9 Jan 2026 08:44:41 +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=1767948282; cv=none; b=NNYQJ7IdVLTucZgQR6gyhPwoJsnVN16pU4u8LUEQUWkpaxXSOQkhMCYf8hWZPkCfVnqKwUs60MNMJ3SdAwDTRAIMjgWbQhNbym1UO8yYFKginr32JDdoVrSlngo6p1kz/W9r1oncue9txwWqqPftgdzfEbzmMzwJoNL5gFiN18E= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767948282; c=relaxed/simple; bh=sazsN0oeUYHYmnMpAFAzwhhfQCumopnAD0FOsYp4zss=; h=Message-ID:Date:MIME-Version:Cc:Subject:To:References:From: In-Reply-To:Content-Type; b=iqT4RPfzw4yP+wNgXmUyVj7I/SvjnUHyLoSFXpkGjDm53xpODzzkYOt+YhiwpVse/aVN8O147X6bVVtjRh85eSmvs0PiDTxgLRv2OL5/G0481ssCRpwl5uPGpYSa3iFZBMbFlLumVpfHhgCQQMfqrz2r9w/xMBIdGPOXcxqj7+M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=AH9wqouL; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="AH9wqouL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8E36CC4CEF1; Fri, 9 Jan 2026 08:44:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767948281; bh=sazsN0oeUYHYmnMpAFAzwhhfQCumopnAD0FOsYp4zss=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=AH9wqouL1l3oXd2PFe3XtJbe2E2xsGGLctqhH7OvXA5uQgtAq9VTyZ4Rro33vkMVQ UpYniigvaDhTxkSap0+TuvPB4gVh3RU9VWta8P/NmM84wLK5Ti3YC/xjqvwF1ELdj4 cYxZHOJZs9dGWgmmm6hA6zaEFuP0f7kBiLIDvjh2tKOx1zYUoGgl8E+4foD8AI3jlw EEJvmrUEvXYxbDfHiJ/R+zTQaeIvZvoymisGBG43Y72sOgPWLh3sL1nrpO8ikkD4EM bPgcP5xhqFHoxHLdpKbjbbL3pLsW9amveLLkHcQO4iWBBHBK3X4gpap8FIYer8J12/ SKwL9hS15kL3A== Message-ID: <8c13ca69-a08a-41c7-bbef-0a79a5f44f93@kernel.org> Date: Fri, 9 Jan 2026 16:44:53 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: chao@kernel.org, jaegeuk@kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH] f2fs: fix to prevent clearing immutable for large folio supported inode To: Barry Song <21cnbao@gmail.com> References: <20260109024716.12047-1-chao@kernel.org> <2cdd4281-7e37-4dd0-91b1-1ab16ef772aa@kernel.org> Content-Language: en-US From: Chao Yu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 1/9/2026 11:57 AM, Barry Song wrote: > On Fri, Jan 9, 2026 at 4:45 PM Chao Yu wrote: >> >> On 1/9/2026 11:05 AM, Barry Song wrote: >>> On Fri, Jan 9, 2026 at 3:47 PM Chao Yu wrote: >>>> >>>> Below testcase can change large folio supported inode from immutable >>>> to mutable, it's not as expected, let's add a new check condition in >>>> f2fs_setflags_common() to detect and reject it. >>>> >>>> - dd if=/dev/zero of=/mnt/f2fs/test bs=32k count=4 >>>> - f2fs_io setflags immutable /mnt/f2fs/test >>>> - echo 3 > /proc/sys/vm/drop_caches >>>> : to reload inode with large folio >>>> - f2fs_io read 32 0 1 mmap 0 0 /mnt/f2fs/test >>>> - f2fs_io clearflags immutable /mnt/f2fs/test >>>> >>>> Signed-off-by: Chao Yu >>>> --- >>>> fs/f2fs/file.c | 6 ++++++ >>>> 1 file changed, 6 insertions(+) >>>> >>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c >>>> index ce291f152bc3..f7f9da0b215f 100644 >>>> --- a/fs/f2fs/file.c >>>> +++ b/fs/f2fs/file.c >>>> @@ -2155,6 +2155,12 @@ static int f2fs_setflags_common(struct inode *inode, u32 iflags, u32 mask) >>>> } >>>> } >>>> >>>> + if ((iflags ^ masked_flags) & F2FS_IMMUTABLE_FL) { >>>> + if ((masked_flags & F2FS_IMMUTABLE_FL) && >>>> + mapping_large_folio_support(inode->i_mapping)) >>>> + return -EINVAL; >>> >> >> Barry, >> >> I noticed that we are allowed to clear immutable if large folio are supported >> in target inode, since we can prevent to open w/ write permission in ->open after >> immutable is cleared, see details in f2fs doc below. >> >> So, anyway, I guess my patch should be ignored. >> >> Per-file Read-Only Large Folio Support >> -------------------------------------- >> >> F2FS implements large folio support on the read path to leverage high-order >> page allocation for significant performance gains. To minimize code complexity, >> this support is currently excluded from the write path, which requires handling >> complex optimizations such as compression and block allocation modes. >> >> This optional feature is triggered only when a file's immutable bit is set. >> Consequently, F2FS will return EOPNOTSUPP if a user attempts to open a cached >> file with write permissions, even immediately after clearing the bit. Write >> access is only restored once the cached inode is dropped. The usage flow is >> demonstrated below: >> >> .. code-block:: >> >> # f2fs_io setflags immutable /data/testfile_read_seq >> >> /* flush and reload the inode to enable the large folio */ >> # sync && echo 3 > /proc/sys/vm/drop_caches >> >> /* mmap(MAP_POPULATE) + mlock() */ >> # f2fs_io read 128 0 1024 mmap 1 0 /data/testfile_read_seq >> >> /* mmap() + fadvise(POSIX_FADV_WILLNEED) + mlock() */ >> # f2fs_io read 128 0 1024 fadvise 1 0 /data/testfile_read_seq >> >> /* mmap() + mlock2(MLOCK_ONFAULT) + madvise(MADV_POPULATE_READ) */ >> # f2fs_io read 128 0 1024 madvise 1 0 /data/testfile_read_seq >> >> # f2fs_io clearflags immutable /data/testfile_read_seq >> >> # f2fs_io write 1 0 1 zero buffered /data/testfile_read_seq >> Failed to open /mnt/test/test: Operation not supported >> >> /* flush and reload the inode to disable the large folio */ >> # sync && echo 3 > /proc/sys/vm/drop_caches > > Right, I see. The only concern is that this would require dropping > the page cache for the entire system, rather than for a single inode. Yes, maybe, one way to avoid "sync && echo 3" is introducing a new ioctl interface to hold inode's parent lock, and call d_invalidate(inode_dentry) to evict the inode which is not opened by anyone. > > >> >> # f2fs_io write 1 0 1 zero buffered /data/testfile_read_seq >> Written 4096 bytes with pattern = zero, total_time = 29 us, max_latency = 28 us >> >> # rm /data/testfile_read_seq >> >>> Hi Yu, I find it a bit odd to prevent unsetting immutable solely >>> because large folios are in use. If unsetting immutable is considered >>> unexpected behavior, it should be disallowed regardless of whether >>> large folios are used, and apply equally in both cases. >> >> To confirm, you mean if clearing immutable is considered unexpected behavior, >> we need to prevent clearing immutable for inode which doesn't enable large folio? > > Right. It feels unfair to prevent clearing immutable solely because > the file happens to have large folios. > >> >>> >>> I'm not sure whether reverting the large folios setting is the >>> better approach: >>> truncate_pagecache(inode, inode->i_size); >>> mapping_set_folio_order_range(inode->i_mapping, 0, 0); >> >> If we want to support reverting the large folios setting dynamically as you >> proposed above, it need to consider more race case and corner case, so, a >> little bit complicated. > > Right. The idea is to truncate the page cache via > truncate_pagecache(inode, 0) and set the maximum page-cache order > to 0. That said, we still need to consider whether any related > locks are held. > > From the comment, it seems that we may need to hold i_rwsem and > invalidate_lock. w/ above locks, it seems there is still a race condition as below: f2fs_fileattr_set read - f2fs_setflags_common - truncate_pagecache - f2fs_read_data_large_folio : read large folios - mapping_set_folio_order_range Thanks, > > /** > * truncate_inode_pages - truncate *all* the pages from an offset > * @mapping: mapping to truncate > * @lstart: offset from which to truncate > * > * Called under (and serialised by) inode->i_rwsem and > * mapping->invalidate_lock. > * > * ... > */ > void truncate_inode_pages(struct address_space *mapping, loff_t lstart) > { > truncate_inode_pages_range(mapping, lstart, (loff_t)-1); > } > EXPORT_SYMBOL(truncate_inode_pages); > > > If clearing immutable is indeed rare, we may leave this as is, since > writes are not supported until the page cache is fully dropped. > Eventually, we will support large folios on non-immutable files. > > Thanks > Barry