linux-kernel - Re: [PATCH v1] rcu: Fix and improve RCU read lock checks when !CONFIG_DEBUG_LOCK

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Date:   Thu, 13 Jul 2023 12:51:34 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     paulmck@...nel.org
Cc:     Joel Fernandes <joel@...lfernandes.org>,
        Sandeep Dhavale <dhavale@...gle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Josh Triplett <josh@...htriplett.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Zqiang <qiang.zhang1211@...il.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        linux-erofs@...ts.ozlabs.org, xiang@...nel.org,
        Will Shiu <Will.Shiu@...iatek.com>, kernel-team@...roid.com,
        rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v1] rcu: Fix and improve RCU read lock checks when
 !CONFIG_DEBUG_LOCK_ALLOC



On 2023/7/13 12:27, Paul E. McKenney wrote:
> On Thu, Jul 13, 2023 at 10:02:17AM +0800, Gao Xiang wrote:
>>
>>

... sorry forget some.

> 
> One additional question...  What is your plan for kernels built with
> CONFIG_PREEMPT_COUNT=n?  After all, in such kernels, there is no way
> that I know of for code to determine whether it is in an RCU read-side
> critical section, holding a spinlock, or running with preemption disabled.

I'm not sure if Android (or all targetted) users use or care about
this configuration (CONFIG_PREEMPT_COUNT=n), personally I think
for such configuration we could just fall back to the workqueue
approach all the time.

Anyway, such optimization really comes from real workloads /
experience, users don't live well without such mitigation.

Thanks,
Gao Xiang

> 
> 						Thanx, Paul