From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from m16.mail.126.com (m16.mail.126.com [220.197.31.6]) (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 7DDC63F58E9; Thu, 3 Sep 2026 06:38:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=220.197.31.6 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788417505; cv=none; b=tvVbooxBdef/0ziOvk2MvBq6/qJZ6ck5ohO2EsUjw54TvQ9s+P4ZqjHZs/oayXY52axq5PPSFRJ+0ju3A9xHscEAsbkg777jPU3psprKDgWX7HGLmdUGnWqG+lcq3gjC+cxTZqCvTj3okKHGbwQtsPjK0WSMWy9QvM96JNx9T3w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788417505; c=relaxed/simple; bh=WHzN8whD/sPVFMbaTppMqhjZBhAguwvoXnPwSSu9ehY=; h=Message-ID:Date:From:MIME-Version:To:CC:Subject:References: In-Reply-To:Content-Type; b=hx9dhEU76ypWA2UQVJt2QFXO+uME6Y8SvFnsRlstvel6c96K1qfNU6L1ilM+P1C4nOy3CPmsaCxEoqluV0I+n6ga4WpCeL9BocyE5mLjUy0iA5skJqqNexOjBzyolHyYAAJ3e0YsQRqThpCF1CykD/52QCdX4B6iWD3Do5lQid0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=126.com; spf=pass smtp.mailfrom=126.com; dkim=pass (1024-bit key) header.d=126.com header.i=@126.com header.b=dh/fCS7G; arc=none smtp.client-ip=220.197.31.6 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=126.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=126.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=126.com header.i=@126.com header.b="dh/fCS7G" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=126.com; s=s110527; h=Message-ID:Date:From:MIME-Version:To:Subject: Content-Type; bh=QhhhQWqk/C4nR9X6FXtttU/PKvCAIlbq/hLOZ5YeK4Y=; b=dh/fCS7G0OJqoZRU1MMXilaZclxQLnSGH9pxl1+hGwO2xyhIhXmRNiDba0i10v /Ov6SbbD5ffZT01ipwBqjVz0pfNGwxyp6af9gINSOkapB+ih2a/dz2gu5PMR3OEr BjWkQLnVic2s2jKbOY55AwXOknOlYrSV37dEE7YhVLv88= Received: from localhost.localdomain (unknown []) by gzga-smtp-mtada-g1-0 (Coremail) with SMTP id _____wDnt5mpFZlq41LHAA--.43306S2; Thu, 03 Sep 2026 14:37:30 +0800 (CST) Message-ID: <6A99158E.2040006@126.com> Date: Thu, 03 Sep 2026 14:37:02 +0800 From: Hongling Zeng User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 To: liubaolin , Hongling Zeng , linkinjeon@kernel.org, hyc.lee@gmail.com CC: ntfs@lists.linux.dev, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 1/2] ntfs: fix volume flag update races References: <20260903012104.185926-1-zenghongling@kylinos.cn> In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-CM-TRANSID:_____wDnt5mpFZlq41LHAA--.43306S2 X-Coremail-Antispam: 1Uf129KBjvJXoW3WF4UWrWUCF18ZFWkGw1xKrg_yoWfAr4fpr s2yF9rKa1qyr1xuws7t3yIga1S934kGr48Cry7Jw1av3s0kr18XFy8K3WrZa4vyr9rAw1I qFWUtrW3uw1UZFDanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07j-sqJUUUUU= X-CM-SenderInfo: x2kr0wpolqwiqxrzqiyswou0bp/xtbBrgpwQWqZFarT4QAA3r 在 2026年09月03日 11:01, liubaolin 写道: > > > 在 2026/9/3 09:21, Hongling Zeng 写道: >> ntfs_set_volume_flags() and ntfs_clear_volume_flags() both read >> vol->vol_flags outside any lock to compute the new value before handing >> it to ntfs_write_volume_flags(), which only takes ni->mrec_lock around >> the actual write. The read-modify-write is therefore not atomic, and two >> concurrent callers can lose an update: ntfs_sync_fs() may derive a >> "clean" value from vol->vol_flags while a writer concurrently records an >> error and sets VOLUME_IS_DIRTY; the locked write then silently >> overwrites the freshly-set dirty bit. The on-disk volume looks clean >> despite the recorded errors, so chkdsk will not run on the next mount >> and corrupted metadata can persist. >> >> Fix by moving the read-modify-write inside the mrec_lock: pass the bits >> to set and to clear separately, and combine them with the current flag >> state under the lock inside ntfs_write_volume_flags(). The set/clear >> helpers pass only the bits to modify, not the complete flag state. The >> bit manipulation is done on CPU-endian values, and the result is >> converted back to little-endian before storing it. The wrappers keep >> their signatures so callers are unchanged. >> >> Cc: stable@vger.kernel.org >> Signed-off-by: Hongling Zeng >> --- >> - Also fix the ntfs_sync_fs() race by checking NVolErrors() and clearing >> VOLUME_IS_DIRTY under ni->mrec_lock. >> - Keep ntfs_set_volume_flags() and ntfs_clear_volume_flags() semantics >> unchanged. >> - Do not tie setting VOLUME_IS_DIRTY to NVolSetErrors() in the generic >> set helper. >> --- >> fs/ntfs/super.c | 62 +++++++++++++++++++++++++++++++++++-------------- >> 1 file changed, 45 insertions(+), 17 deletions(-) >> >> diff --git a/fs/ntfs/super.c b/fs/ntfs/super.c >> index a1813093222b..a7977b95b967 100644 >> --- a/fs/ntfs/super.c >> +++ b/fs/ntfs/super.c >> @@ -353,31 +353,45 @@ void ntfs_handle_error(struct super_block *sb) >> } >> /* >> - * ntfs_write_volume_flags - write new flags to the volume >> information flags >> + * ntfs_write_volume_flags - apply flag changes to the volume >> information flags >> * @vol: ntfs volume on which to modify the flags >> - * @flags: new flags value for the volume information flags >> + * @set_bits: bits to set in the volume information flags >> + * @clear_bits: bits to clear in the volume information flags >> * >> * Internal function. You probably want to use >> ntfs_{set,clear}_volume_flags() >> * instead (see below). >> * >> - * Replace the volume information flags on the volume @vol with the >> value >> - * supplied in @flags. Note, this overwrites the volume information >> flags, so >> - * make sure to combine the flags you want to modify with the old >> flags and use >> - * the result when calling ntfs_write_volume_flags(). >> + * Combine @set_bits and @clear_bits with the current in-memory flag >> state and >> + * write the result back. The set/clear helpers pass only the bits >> to modify, >> + * not the complete flag state. The read-modify-write happens under >> + * ni->mrec_lock so that concurrent set/clear operations cannot lose >> updates. >> + * All bit manipulation is done on CPU-endian values, and the result is >> + * converted back to little-endian before storing it. >> * >> * Return 0 on success and -errno on error. >> */ >> -static int ntfs_write_volume_flags(struct ntfs_volume *vol, const >> __le16 flags) >> +static int ntfs_write_volume_flags(struct ntfs_volume *vol, >> + const __le16 set_bits, const __le16 clear_bits, >> + const bool skip_if_errors) >> { >> struct ntfs_inode *ni = NTFS_I(vol->vol_ino); >> struct volume_information *vi; >> struct ntfs_attr_search_ctx *ctx; >> + u16 flags; >> int err; >> - ntfs_debug("Entering, old flags = 0x%x, new flags = 0x%x.", >> - le16_to_cpu(vol->vol_flags), le16_to_cpu(flags)); >> mutex_lock(&ni->mrec_lock); >> - if (vol->vol_flags == flags) >> + >> + if (skip_if_errors && NVolErrors(vol)) >> + goto done; >> + >> + flags = le16_to_cpu(vol->vol_flags); >> + flags |= le16_to_cpu(set_bits) & le16_to_cpu(VOLUME_FLAGS_MASK); >> + flags &= ~(le16_to_cpu(clear_bits) & >> le16_to_cpu(VOLUME_FLAGS_MASK)); >> + ntfs_debug("Entering, old flags = 0x%x, new flags = 0x%x.", >> + le16_to_cpu(vol->vol_flags), flags); >> + >> + if (le16_to_cpu(vol->vol_flags) == flags) >> goto done; >> ctx = ntfs_attr_get_search_ctx(ni, NULL); >> @@ -393,7 +407,7 @@ static int ntfs_write_volume_flags(struct >> ntfs_volume *vol, const __le16 flags) >> vi = (struct volume_information *)((u8 *)ctx->attr + >> le16_to_cpu(ctx->attr->data.resident.value_offset)); >> - vol->vol_flags = vi->flags = flags; >> + vol->vol_flags = vi->flags = cpu_to_le16(flags); >> mark_mft_record_dirty(ctx->ntfs_ino); >> ntfs_attr_put_search_ctx(ctx); >> done: >> @@ -414,13 +428,14 @@ static int ntfs_write_volume_flags(struct >> ntfs_volume *vol, const __le16 flags) >> * @flags: flags to set on the volume >> * >> * Set the bits in @flags in the volume information flags on the >> volume @vol. >> + * The bits are combined with the current flag state under the lock in >> + * ntfs_write_volume_flags(), so concurrent updates are not lost. >> * >> * Return 0 on success and -errno on error. >> */ >> int ntfs_set_volume_flags(struct ntfs_volume *vol, __le16 flags) >> { >> - flags &= VOLUME_FLAGS_MASK; >> - return ntfs_write_volume_flags(vol, vol->vol_flags | flags); >> + return ntfs_write_volume_flags(vol, flags, 0, false); >> } >> /* >> @@ -429,14 +444,27 @@ int ntfs_set_volume_flags(struct ntfs_volume >> *vol, __le16 flags) >> * @flags: flags to clear on the volume >> * >> * Clear the bits in @flags in the volume information flags on the >> volume @vol. >> + * The bits are combined with the current flag state under the lock in >> + * ntfs_write_volume_flags(), so concurrent updates are not lost. >> * >> * Return 0 on success and -errno on error. >> */ >> int ntfs_clear_volume_flags(struct ntfs_volume *vol, __le16 flags) >> { >> - flags &= VOLUME_FLAGS_MASK; >> - flags = vol->vol_flags & cpu_to_le16(~le16_to_cpu(flags)); >> - return ntfs_write_volume_flags(vol, flags); >> + return ntfs_write_volume_flags(vol, 0, flags, false); >> +} >> + >> +/* >> + * ntfs_clear_volume_dirty_if_no_errors - clear dirty bit if no >> errors exist >> + * @vol: ntfs volume whose dirty bit should be cleared >> + * >> + * Check NVolErrors() and clear VOLUME_IS_DIRTY under the same >> mrec_lock so >> + * ntfs_sync_fs() cannot clear the dirty bit after a concurrent >> error has been >> + * recorded. >> + */ >> +static int ntfs_clear_volume_dirty_if_no_errors(struct ntfs_volume >> *vol) >> +{ >> + return ntfs_write_volume_flags(vol, 0, VOLUME_IS_DIRTY, true); >> } >> int ntfs_write_volume_label(struct ntfs_volume *vol, char *label) >> @@ -1862,7 +1890,7 @@ static int ntfs_sync_fs(struct super_block *sb, >> int wait) >> return 0; >> /* If there are some dirty buffers in the bdev inode */ >> - if (ntfs_clear_volume_flags(vol, VOLUME_IS_DIRTY)) { >> + if (ntfs_clear_volume_dirty_if_no_errors(vol)) { >> ntfs_warning(sb, "Failed to clear dirty bit in volume >> information flags. Run chkdsk."); >> err = -EIO; >> } > > Hi Hongling, > Patch 1 fixes the race in ntfs_sync_fs(), but there are two other > sites with the same check-outside-lock-then-clear-inside-lock pattern: > > 1. super.c:315 (ntfs_reconfigure, remount read-only path) > 2. super.c:1755 (ntfs_put_super, umount path) > > Both use: > if (!NVolErrors(vol)) { // check outside lock > if (ntfs_clear_volume_flags(vol, VOLUME_IS_DIRTY)) // clear > inside lock > > The same race can occur: if an error thread sets NVolErrors() and the > dirty bit after the check but before the lock acquisition, the clear > operation will overwrite the freshly-set dirty bit. > > Although the race window is much narrower for remount/umount, should > these two sites also be converted to use > ntfs_clear_volume_dirty_if_no_errors() for consistency? > > Reviewed-by: Baolin Liu > > > Thanks, > Baolin. Thanks for the careful reading These two sites cannot actually race ntfs_sync_fs(): ntfs_reconfigure() (via do_remount()) and ntfs_put_super() (via generic_shutdown_super()) both run with sb->s_umount held for write, while the sync(2)/syncfs(2) paths only take it for read through iterate_supers(). So the check and the clear inside ntfs_clear_volume_flags() are effectively a single non-interleavable pair with respect to sync — the window is not merely narrow but structurally closed. We deliberately keep ntfs_clear_volume_dirty_if_no_errors() for the paths that can genuinely race sync (currently only ntfs_sync_fs() itself), so converting these two would blur that line rather than improve consistency.