From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 AFF514DA9A9; Thu, 17 Sep 2026 15:50:38 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789660244; cv=none; b=FmQae5EfWsAlizD2hjARciY8d/p8JJcADNnGFOBYOyviaE4Y4tDiwjvibPcB6Klr1VTjeHnKQhh9J9l1tk+bjM0KdnVu2kLUU3JFf/JIv1vIpDgUZn17IpRsERn3rh92sEX5cloJCKeGb1hxR+e3baj3EQdznn0YUZoZn+31fTk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789660244; c=relaxed/simple; bh=YukoIh3H93hzzFJtyz7HvyoEeRTcVpu/zAcuxk28+dw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=BT38r+7JEXjyuCfV489stBEFjEQbjTVfEO5KJo6uBMVHAIkgTVShGE2gTb6WxxW/Ca0E//XVY6RQLlF6uTVHtdiTip36PhW5l8JjUOgerJuZOmsTZQszVdf+qK1xjPkLkI4mrJIwEMBlkPpmui2tMt7L7S7Jh9BOI3mzPshDLlk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=GTgAnmhm; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="GTgAnmhm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 394001F000FF; Thu, 17 Sep 2026 15:50:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789660235; bh=K0R2O8u6dEx7RdMZFX5XaCs4N8ABsRoVq24yRhHaU48=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=GTgAnmhmEBtvQRaKkpnDk/4bmn5VK54HkBjKReYOAAEYogc6k0YEAbkEyDBCS7LRs 1qQy+29J733LH4r0TDf2Kuhnf5Fj1+C/LLtfsjUKcBG/+h+Xalw4jQu2q4xT0ypVLX T/KBiiO9rdfcgTx7mqdWTmTc1gX0r81psbVhbVAI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Moritz Tanner , Lars Ellenberg , "Christian Brauner (Amutable)" Subject: [PATCH 7.2 523/733] fs: dont return -EINVAL for successful nested thaw Date: Thu, 17 Sep 2026 16:13:51 +0100 Message-ID: <20260917151405.202069445@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260917151350.597953846@linuxfoundation.org> References: <20260917151350.597953846@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Moritz Tanner commit fe967191e5851ea79818c5fe4e781c3882139218 upstream. Commit 7366f8b6fc6a ("fs: handle freezing from multiple devices") replaced the freeze_holders bitmask with per-holder counters to allow nested freezes. In the bitmask version, a thaw that released a shared hold while another holder remained returned 0. Since the rework, thaw_super_locked() drops the freeze reference via freeze_dec() but then returns -EINVAL when other freezers remain, misinforming the caller: the thaw did succeed, the superblock just stays frozen for the remaining holders. This breaks bdev-initiated freezing. When a filesystem is frozen with FIFREEZE and additionally frozen via bdev_freeze() -- which nests by design, see fs_bdev_freeze() -- the subsequent bdev_thaw() receives -EINVAL from the holder op although its freeze reference was dropped, and therefore keeps bd_fsfreeze_count elevated. Then device-mapper's unlock_fs() ignores bdev_thaw()'s return value, so nothing rebalances the count. After the user's FITHAW and umount, the block device can never be mounted again: dm-1: Can't mount, blockdev is frozen There is no way for userspace to drop the leaked count; only destroying the block device (or a reboot) recovers the device. Reproducer (any kernel since v6.8): dmsetup create dut --table "0 $(blockdev --getsz "$DEV") linear $DEV 0" mkfs.ext4 /dev/mapper/dut mount /dev/mapper/dut /mnt fsfreeze --freeze /mnt # freeze_ucount == 1 dmsetup suspend dut # bd_fsfreeze_count == 1, ucount == 2 dmsetup resume dut # ucount 2 -> 1, but thaw_super() # returns -EINVAL, so bdev_thaw() # keeps bd_fsfreeze_count at 1 fsfreeze --unfreeze /mnt # filesystem thaws fine umount /mnt mount /dev/mapper/dut /mnt # EBUSY, forever The same happens with fsfreeze held across an LVM snapshot of the origin volume. fs_bdev_thaw()'s documentation already describes the intended semantics: "If this function returns zero it doesn't mean that the filesystem is unfrozen as it may have been frozen multiple times". Restore them by returning 0 when a nested thaw drops its hold while other freezers remain. Thawing without holding a freeze still fails with -EINVAL as may_unfreeze() rejects that case before the reference count is touched. Fixes: 7366f8b6fc6a ("fs: handle freezing from multiple devices") Cc: stable@vger.kernel.org # needs adjustments for < 6.17 (no may_unfreeze()) Signed-off-by: Moritz Tanner Link: https://patch.msgid.link/20260821085451.65206-1-moritz.tanner@linbit.com Tested-by: Lars Ellenberg Reviewed-by: Lars Ellenberg Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Greg Kroah-Hartman --- fs/super.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) --- a/fs/super.c +++ b/fs/super.c @@ -2122,11 +2122,14 @@ static int thaw_super_locked(struct supe goto out_unlock; /* - * All freezers share a single active reference. - * So just unlock in case there are any left. + * All freezers share a single active reference. If other freezers + * remain, drop our hold and report success; the superblock stays + * frozen until the last holder thaws it. */ - if (freeze_dec(sb, who)) + if (freeze_dec(sb, who)) { + error = 0; goto out_unlock; + } if (sb_rdonly(sb)) { sb->s_writers.frozen = SB_UNFROZEN;