Re: [PATCH mm-unstable hotfix] mm/zswap: fix zswap_pools_lock usages after changing to percpu_ref

[Chengming Zhou <chengming.zhou@linux.dev>]

On 2024/2/28 23:24, Matthew Wilcox wrote:
> On Wed, Feb 28, 2024 at 03:18:32PM +0000, Chengming Zhou wrote:
>> Now the release of zswap pool is controlled by percpu_ref, its release
>> callback (__zswap_pool_empty()) will be called when percpu_ref hit 0.
>> But this release callback may potentially be called from RCU callback
>> context by percpu_ref_kill(), which maybe in the interrupt context.
>>
>> So we need to use spin_lock_irqsave() and spin_unlock_irqrestore()
>> in the release callback: __zswap_pool_empty(). In other task context
>> places, spin_lock_irq() and spin_unlock_irq() are enough to avoid
>> potential deadlock.
> 
> RCU callback context is BH, not IRQ, so it's enough to use
> spin_lock_bh(), no?

You're right, it's the softirq context, so spin_lock_bh() is enough.

Thanks!