Re: [PATCH] mm/kfence: add reboot notifier to disable KFENCE on shutdown

[Andrew Morton <akpm@linux-foundation.org>]

On Wed, 26 Nov 2025 09:46:18 -0800 Breno Leitao <leitao@debian.org> wrote:

> During system shutdown, KFENCE can cause IPI synchronization issues if
> it remains active through the reboot process. To prevent this, register
> a reboot notifier that disables KFENCE and cancels any pending timer
> work early in the shutdown sequence.
> 
> This is only necessary when CONFIG_KFENCE_STATIC_KEYS is enabled, as
> this configuration sends IPIs that can interfere with shutdown. Without
> static keys, no IPIs are generated and KFENCE can safely remain active.
> 
> The notifier uses maximum priority (INT_MAX) to ensure KFENCE shuts
> down before other subsystems that might still depend on stable memory
> allocation behavior.
> 
> This fixes a late kexec CSD lockup[1] when kfence is trying to IPI a CPU
> that is busy in a IRQ-disabled context printing characters to the
> console.
> 
> Link: https://lore.kernel.org/all/sqwajvt7utnt463tzxgwu2yctyn5m6bjwrslsnupfexeml6hkd@v6sqmpbu3vvu/ [1]

6.13 kernels and earlier, so I assume we'll want a cc:stable on this. 
And I assume there's really no identifiable Fixes: target.