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… (CVE-2026-98818)

The Linux kernel vulnerability CVE-2026-98818 concerns a deadlock caused by __kfree_rcu_sheaf() waking up the kswapd kernel thread while holding the pi_lock raw spinlock. Since kfree_rcu() can be called under pi_lock, waking up kswapd (which also acquires pi_lock) leads to a circular locking dependency and deadlock. The issue was confirmed using a kernel with lockdep instrumentation, revealing a complex lock dependency chain involving pi_lock and kswapd_wait. The fix prevents kfree_rcu() from waking kswapd under pi_lock, eliminating the deadlock scenario.

The vulnerability could cause a kernel deadlock, potentially freezing affected systems or kernel threads. However, reproducing the deadlock was not straightforward and required specific conditions. There is no indication of direct security compromise such as privilege escalation or data corruption, but system stability could be affected.

A fix has been implemented in the Linux kernel to prevent kfree_rcu() from waking kswapd under pi_lock, thereby avoiding the deadlock. Users should apply the official kernel updates that include this fix. Since this is a kernel-level issue, updating to a patched kernel version is the recommended remediation.