# CVE-2026-98818: mm/slab: do not wake up kswapd in __kfree_rcu_sheaf()

CVE-2026-98818 is fixed in linux on 1 platform by DEBIAN-CVE-2026-98818 (version 7.2.10-1), released October 19, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-98818
- Priority: Routine
- CVSS: n/a
- EPSS: 0.0016
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 18, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-98818

## Description

In the Linux kernel, the following vulnerability has been resolved:  mm/slab: do not wake up kswapd in __kfree_rcu_sheaf()  Since kfree_rcu() can be called under pi_lock (a raw spinlock in the scheduler), kfree_rcu() itself should never allocate memory with __GFP_KSWAPD_RECLAIM as waking up kswapd ends up acquiring pi_lock, which leads to a deadlock.  Reproducing the issue even intentionally was not straightforward. The set_cpus_allowed_force() path that is called under pi_lock is exercised very rarely, and competing tasks that allocate memory will most likely wake kswapd up.  Therefore the existence of the deadlock was verified with a modified kernel that has a lockdep map for waking up kswapd:    ======================================================   WARNING: possible circular locking dependency detected   7.2.0-rc1-slab-for-next+ #10 Not tainted   ------------------------------------------------------   git/6660 is trying to acquire lock:   ffff8e524533c550 (&p->pi_lock){-.-.}-{2:2}, at: _raw_spin_lock_irqsave+0x12/0x20    but task is already holding lock:   ffff8e57bffff1a0 (&pgdat->kswapd_wait){....}-{3:3}, at: _raw_spin_lock_irqsave+0x12/0x20    which lock already depends on the new lock.    the existing dependency chain (in reverse order) is:    -> #2 (&pgdat->kswapd_wait){....}-{3:3}:          __lock_acquire+0x5a4/0xc50          lock_acquire.part.0+0xb7/0x240          lock_acquire+0x70/0x170          __raw_spin_lock_irqsave+0x44/0x80          _raw_spin_lock_irqsave+0x12/0x20          __wake_up_common_lock+0x31/0xa0          __wake_up+0x20/0x40          kswapd_wakeup_wake+0x7e/0x110          wakeup_kswapd+0x295/0x320          wake_all_kswapds+0xac/0x1a0          __alloc_pages_slowpath.constprop.0+0x282/0xf80          __alloc_frozen_pages_noprof+0x32a/0x360          alloc_slab_page+0x2e/0x160          allocate_slab+0x82/0x420          new_slab+0x52/0xb0          refill_objects+0x13d/0x190          refill_sheaf+0x5d/0xd0          __pcs_replace_empty_main+0x230/0xb10          [...]    -> #1 (kswapd_wakeup){-.-.}-{0:0}:          __lock_acquire+0x5a4/0xc50          lock_sync.part.0+0x75/0x100          lock_sync+0x36/0x70          might_wakeup_kswapd+0x61/0xa0          __kfree_rcu_sheaf+0x33/0xd90          kvfree_call_rcu+0x1d4/0x3b0          set_cpus_allowed_force+0x163/0x220          cpuset_cpus_allowed_fallback+0x18b/0x240          select_fallback_rq+0x1e6/0x250 	 [...]    -> #0 (&p->pi_lock){-.-.}-{2:2}:          check_prev_add+0xe6/0xe00          validate_chain+0x51e/0x6e0          __lock_acquire+0x5a4/0xc50          lock_acquire.part.0+0xb7/0x240          lock_acquire+0x70/0x170          __raw_spin_lock_irqsave+0x44/0x80          _raw_spin_lock_irqsave+0x12/0x20          try_to_wake_up+0x77/0xa90          default_wake_function+0x27/0x60          autoremove_wake_function+0x23/0xb0          __wake_up_common+0xb8/0x170          __wake_up_common_lock+0x51/0xa0          __wake_up+0x20/0x40          kswapd_wakeup_wake+0x7e/0x110          wakeup_kswapd+0x295/0x320          wake_all_kswapds+0xac/0x1a0          __alloc_pages_slowpath.constprop.0+0x282/0xf80          __alloc_frozen_pages_noprof+0x32a/0x360          alloc_slab_page+0x2e/0x160          allocate_slab+0x82/0x420          new_slab+0x52/0xb0          refill_objects+0x13d/0x190          refill_sheaf+0x5d/0xd0          __pcs_replace_empty_main+0x230/0xb10          [...]    other info that might help us debug this:    Chain exists of:     &p->pi_lock --> kswapd_wakeup --> &pgdat->kswapd_wait     Possible unsafe locking scenario:           CPU0                    CPU1          ----                    ----     lock(&pgdat->kswapd_wait);                                  lock(kswapd_wakeup);                                  lock(&pgdat->kswapd_wait);     lock(&p->pi_lock);     *** DEADLOCK ***    3 locks held by git/6660:    #0: ffff8e519f0e9e20 (&type->i_mutex_dir_key#6){++++}-{4:4}, at: lookup_slow+0x2d/0x60    #1: ffffffff8a31c460 (kswapd_wakeup){-.-.}- ---truncated---

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 14 | 7.2.10-1 | [DEBIAN-CVE-2026-98818](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98818.md) | Oct 19, 2026 |

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Data as of 2026-11-09T13:31:49Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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