linux-kernel - Re: [RFC PATCH v1 1/3] locking/lockdep: Fix false warning of check_wait

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Date:   Sun, 11 Jul 2021 12:43:11 -0400
From:   Waiman Long <llong@...hat.com>
To:     Xiongwei Song <sxwjean@...com>, peterz@...radead.org,
        mingo@...hat.com, will@...nel.org, boqun.feng@...il.com
Cc:     linux-kernel@...r.kernel.org, Xiongwei Song <sxwjean@...il.com>
Subject: Re: [RFC PATCH v1 1/3] locking/lockdep: Fix false warning of
 check_wait_context()

On 7/11/21 10:14 AM, Xiongwei Song wrote:
> From: Xiongwei Song <sxwjean@...il.com>
>
> We now always get a "Invalid wait context" warning with
> CONFIG_PROVE_RAW_LOCK_NESTING=y, see the full warning below:
>
> 	[    0.705900] =============================
> 	[    0.706002] [ BUG: Invalid wait context ]
> 	[    0.706180] 5.13.0+ #4 Not tainted
> 	[    0.706349] -----------------------------

I believe the purpose of CONFIG_PROVE_RAW_LOCK_NESTING is experimental 
and it is turned off by default. Turning it on can cause problem as 
shown in your lockdep splat. Limiting it to just PREEMPT_RT will defeat 
its purpose to find potential spinlock nesting problem in non-PREEMPT_RT 
kernel. The point is to fix the issue found, not hiding it from appearing.

Cheers,
Longman