linux-kernel - Re: [PATCH V2] lockdep: fix deadlock issue between lockdep and rcu

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Date: Thu, 1 Feb 2024 13:24:48 -0800
From: Bart Van Assche <bvanassche@....org>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Zhiguo Niu <zhiguo.niu@...soc.com>, peterz@...radead.org,
 mingo@...hat.com, will@...nel.org, longman@...hat.com,
 linux-kernel@...r.kernel.org, niuzhiguo84@...il.com, ke.wang@...soc.com,
 xuewen.yan@...soc.com, Carlos Llamas <cmllamas@...gle.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH V2] lockdep: fix deadlock issue between lockdep and rcu

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.