Received-SPF: pass (google.com: domain of linux-kernel+bounces-48872-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
Message-ID: <1f1691cd-fcc8-4a0b-9d63-bff15c5a52ad@acm.org>
Date: Thu, 1 Feb 2024 13:24:48 -0800
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH V2] lockdep: fix deadlock issue between lockdep and rcu
Content-Language: en-US
To: Boqun Feng <boqun.feng@gmail.com>
Cc: Zhiguo Niu <zhiguo.niu@unisoc.com>, peterz@infradead.org,
 mingo@redhat.com, will@kernel.org, longman@redhat.com,
 linux-kernel@vger.kernel.org, niuzhiguo84@gmail.com, ke.wang@unisoc.com,
 xuewen.yan@unisoc.com, Carlos Llamas <cmllamas@google.com>,
 Greg Kroah-Hartman <gregkh@linuxfoundation.org>
References: <1705477714-10467-1-git-send-email-zhiguo.niu@unisoc.com>
 <cc828212-9a90-430e-8719-e6b19bdab600@acm.org>
 <CAL0jBu-2jrhBzTo+ZneFMpsTsqUMLVQCYCAQKqd6BHjv3-kxhQ@mail.gmail.com>
From: Bart Van Assche <bvanassche@acm.org>
In-Reply-To: <CAL0jBu-2jrhBzTo+ZneFMpsTsqUMLVQCYCAQKqd6BHjv3-kxhQ@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit

On 2/1/24 11:48, Boqun Feng wrote:
> raw_spin_lock_irqsave():
>    lock_acquire():
>      __lock_acquire():
>        validate_chain():
>          lookup_chain_cache_add():
>            graph_lock();
> 
> Basically, every lock acquisition may lock the lockdep graph because
> of dependency checking.

Wouldn't it be simpler to make __lock_acquire() return early if
this_cpu_read(lockdep_recursion) indicates that the graph lock is held?

Thanks,

Bart.