Received-SPF: pass (google.com: domain of linux-kernel+bounces-85274-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Message-ID: <1d920f2c-2f86-46b9-b5d9-b5615284e5c3@linux.dev>
Date: Wed, 28 Feb 2024 23:37:44 +0800
Precedence: bulk
MIME-Version: 1.0
Subject: Re: [PATCH mm-unstable hotfix] mm/zswap: fix zswap_pools_lock usages
 after changing to percpu_ref
Content-Language: en-US
To: Matthew Wilcox <willy@infradead.org>
Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, yosryahmed@google.com,
 nphamcs@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <20240210-zswap-global-lru-v3-2-200495333595@bytedance.com>
 <20240228151832.2431993-1-chengming.zhou@linux.dev>
 <Zd9QFkE2nr5FyYDq@casper.infradead.org>
From: Chengming Zhou <chengming.zhou@linux.dev>
In-Reply-To: <Zd9QFkE2nr5FyYDq@casper.infradead.org>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit

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!