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 50CAC471D15 for ; Wed, 29 Jul 2026 13:54:44 +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=1785333290; cv=none; b=b7d1IFUmBwLt/81TxbF4NZX3mpC9GrwweyTSAWW0ogkFRDrJ9hV2JESKhYuAmIJ6QyWQR7I8hzIDflwo1UCi69eQUlW4/wuc9dsS/1q0U/gAx451vQ3DhtW5g6bJgIKjelNO589bFHqYlv2ehGUqQx+loxcvyF5Cc0B8WFHaVc4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785333290; c=relaxed/simple; bh=vtha1mHdPagNC9wTFBtIFOD5agYBdLYKlJ417mzOmtE=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=XKvRRM49JNyKcb0rkRdhbPslFFGMQxdZe66PKhVQ2LBGTEM3BaoKU/gKxgZ8VqTXXNFZ1AzXcjXBEE+BXMmC+onN5+kBDXFUjQtHf6K0ISu9uUmUviaQxK2dHY61zxrMTwNK/X7QMmdbMJdwQA9TWTTv456SM7cyNw9alVwA2VY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Zvmqynpg; 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="Zvmqynpg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 17B621F000E9; Wed, 29 Jul 2026 13:54:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1785333280; bh=9PgffDJrQm6W7S0UmMMDlaruWq4D698xICj2akUFzx8=; h=Subject:To:Cc:From:Date; b=Zvmqynpg6RcPsjraGMdG1+7WAi9fP4NIkHvvnYIGpyxpcUv+jjTYHaiqRxJCsaWqr y71kCgepTS9vQkr3sfrPznVFjH1RjgMKtoj9GnFFSPyeaPZLM7VAZcJf2auf6/05fo GdnM4we4MN7i8ZxBsDJ4RW3UiePo6kmQ1MyBYg2I= Subject: FAILED: patch "[PATCH] super: fix emergency thaw deadlock on frozen block devices" failed to apply to 6.12-stable tree To: brauner@kernel.org Cc: From: Date: Wed, 29 Jul 2026 15:54:27 +0200 Message-ID: <2026072927-mom-flyover-909f@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.12-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y git checkout FETCH_HEAD git cherry-pick -x 749d7aa0377aae32af8c0a4ad43371e7bf830ab5 # git commit -s git send-email --to '' --in-reply-to '2026072927-mom-flyover-909f@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 749d7aa0377aae32af8c0a4ad43371e7bf830ab5 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Thu, 23 Jul 2026 11:37:05 +0200 Subject: [PATCH] super: fix emergency thaw deadlock on frozen block devices do_thaw_all_callback() calls bdev_thaw() while holding sb->s_umount exclusively. If the block device was frozen via bdev_freeze() dropping the last block layer freeze reference calls fs_bdev_thaw() which reacquires s_umount: do_thaw_all_callback(sb) super_lock_excl(sb) # holds sb->s_umount bdev_thaw(sb->s_bdev) mutex_lock(&bdev->bd_fsfreeze_mutex) # bd_fsfreeze_count drops 1 -> 0 bd_holder_ops->thaw == fs_bdev_thaw get_bdev_super(bdev) bdev_super_lock(bdev, true) super_lock(sb, true) down_write(&sb->s_umount) # same task: deadlock The emergency thaw worker deadlocks against itself holding both s_umount and bd_fsfreeze_mutex. That fscks any subsequent unmount, freeze, or thaw of that filesystem and block device. [ 81.878470] sysrq: Show Blocked State [ 81.880140] task:kworker/0:1 state:D stack:0 pid:11 tgid:11 ppid:2 task_flags:0x4208060 flags:0x00080000 [ 81.884876] Workqueue: events do_thaw_all [ 81.886656] Call Trace: [ 81.887759] [ 81.888763] __schedule+0x579/0x1420 [ 81.890372] schedule+0x3a/0x100 [ 81.891794] schedule_preempt_disabled+0x15/0x30 [ 81.893848] rwsem_down_write_slowpath+0x1ea/0x900 [ 81.895191] ? __pfx_do_thaw_all_callback+0x10/0x10 [ 81.896528] down_write+0xbd/0xc0 [ 81.897505] super_lock+0x91/0x180 [ 81.898457] ? __mutex_lock+0xa99/0x1140 [ 81.900748] ? __mutex_unlock_slowpath+0x1f/0x400 [ 81.902069] bdev_super_lock+0x5b/0x150 [ 81.903132] get_bdev_super+0x10/0x60 [ 81.904042] fs_bdev_thaw+0x23/0xf0 [ 81.904755] bdev_thaw+0x82/0x100 [ 81.905484] do_thaw_all_callback+0x2c/0x50 [ 81.906298] __iterate_supers+0x5d/0x130 [ 81.907067] do_thaw_all+0x20/0x40 [ 81.907739] process_one_work+0x206/0x5e0 [ 81.908545] worker_thread+0x1e2/0x3c0 [ 81.909339] ? __pfx_worker_thread+0x10/0x10 [ 81.910171] kthread+0xf4/0x130 [ 81.910799] ? __pfx_kthread+0x10/0x10 [ 81.911528] ret_from_fork+0x2e2/0x3b0 [ 81.912259] ? __pfx_kthread+0x10/0x10 [ 81.913010] ret_from_fork_asm+0x1a/0x30 [ 81.913806] bdev_super_lock() even documents the violated requirement with lockdep_assert_not_held(&sb->s_umount). Acquiring bd_fsfreeze_mutex under s_umount also inverts the bd_fsfreeze_mutex vs. s_umount ordering established by bdev_{freeze,thaw}() and can thus ABBA against a concurrent block-layer freeze even when the recursive path isn't hit. Fix this by not holding s_umount around the bdev_thaw() loop at all. Pin the superblock with an active reference instead as filesystems_freeze_callback() does. The active reference keeps the superblock from being shut down and so ->s_bdev stays valid without holding s_umount. The block-layer-held freeze is dropped by fs_bdev_thaw() with FREEZE_MAY_NEST | FREEZE_HOLDER_USERSPACE exactly as a regular unfreeze would and thaw_super_locked() handles filesystem-level freezes as before. The emergency thaw path has deadlocked like this in one form or another for a long long time but the current exclusively-held shape dates back to commit [1] where thaw_bdev() already ended in thaw_super() with s_umount held by do_thaw_all_callback(). Fixes: 08fdc8a0138a ("buffer.c: call thaw_super during emergency thaw") [1] Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260723-work-super-emergency_thaw-v1-1-7c315c600245@kernel.org Signed-off-by: Christian Brauner (Amutable) diff --git a/fs/super.c b/fs/super.c index 70dcb07e7fa5..ffdcc6a2e0de 100644 --- a/fs/super.c +++ b/fs/super.c @@ -1082,16 +1082,30 @@ void emergency_remount(void) } } +static inline bool get_active_super(struct super_block *sb) +{ + bool active = false; + + if (super_lock_excl(sb)) { + active = atomic_inc_not_zero(&sb->s_active); + super_unlock_excl(sb); + } + return active; +} + static void do_thaw_all_callback(struct super_block *sb, void *unused) { - if (!super_lock_excl(sb)) + if (!get_active_super(sb)) return; + /* fs_bdev_thaw() acquires s_umount so it must not be held here */ if (IS_ENABLED(CONFIG_BLOCK)) while (sb->s_bdev && !bdev_thaw(sb->s_bdev)) pr_warn("Emergency Thaw on %pg\n", sb->s_bdev); - thaw_super_locked(sb, FREEZE_HOLDER_USERSPACE, NULL); + if (super_lock_excl(sb)) + thaw_super_locked(sb, FREEZE_HOLDER_USERSPACE, NULL); + deactivate_super(sb); } static void do_thaw_all(struct work_struct *work) @@ -1117,17 +1131,6 @@ void emergency_thaw_all(void) } } -static inline bool get_active_super(struct super_block *sb) -{ - bool active = false; - - if (super_lock_excl(sb)) { - active = atomic_inc_not_zero(&sb->s_active); - super_unlock_excl(sb); - } - return active; -} - static const char *filesystems_freeze_ptr = "filesystems_freeze"; static void filesystems_freeze_callback(struct super_block *sb, void *freeze_all_ptr)