Re: [PATCH v4 00/12] mm: make userland page table freeing RCU-safe

[Matthew Wilcox]

On Tue, Sep 22, 2026 at 04:35:31PM +0100, Lorenzo Stoakes (ARM) wrote:
> m68k-motorola required the biggest change - since RCU page table freeing
> uses call_rcu(), this means page table freeing can arise from softirq
> context.
> 
> This was fixed with an IRQ-safe spin lock used in both get_pointer_table()
> and free_pointer_table().

You don't need to use an irq-safe spinlock for softirqs.  It does work,
but it's overkill since it disables hardirqs.  If you use spin_lock_bh(),
only softirqs are prevented from running (and it's safe to call
spin_lock_bh() when in softirq context, just like it's safe to call
spin_lock_irqsave() in hardirq or softirq context).