CVE-2026-68132super: fix emergency thaw deadlock on frozen block devices

In the Linux kernel, the following vulnerability has been resolved: 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] <TASK> [ 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] </TASK> 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().

CVSS

Not yet scored

Weakness (CWE)

Not given

Known exploited

Not in CISA's KEV catalog

EPSS (exploitation in the next 30 days)

Not loaded for this CVE

Assigned by

Linux

NVD analysis

Received

Record last updated

Aug 23, 2026

First seen by InfoSec Signals

Oct 9, 2026

The CVE record on cve.org · NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.