linux-kernel - Re: [PATCH 07/14] x86: Use lockdep to assert IRQs are disabled/enabled

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Date:   Fri, 3 Nov 2017 15:25:07 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 07/14] x86: Use lockdep to assert IRQs are disabled/enabled

2017-10-22 11:20 UTC+02:00, Peter Zijlstra <peterz@...radead.org>:
> On Fri, Oct 20, 2017 at 02:56:04AM +0200, Frederic Weisbecker wrote:
>> diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
>> index 03505ff..b4f3a55 100644
>> --- a/arch/x86/entry/common.c
>> +++ b/arch/x86/entry/common.c
>> @@ -186,7 +186,7 @@ __visible inline void prepare_exit_to_usermode(struct
>> pt_regs *regs)
>>
>>  	addr_limit_user_check();
>>
>> -	if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
>> +	if (!lockdep_assert_irqs_disabled())
>>  		local_irq_disable();
>>
>>  	lockdep_sys_exit();
>
> So this is the only site that ever uses the return value; and for this
> you've chosen the wrong value for !CONFIG_PROVE_LOCKING (namely 1),
> resulting in an unconditional CLI here for !lockdep kernels.

Hmm, it should be the opposite. The assertion maps to 1 for
!CONFIG_PROVE_LOCKING
but we are testing with "!".

> How about we replace that whole thing with a simple:
>
> 	lockdep_assert_irqs_disabled();
>
> And leave it at that, allowing us to remove the return value thing
> entirely.
>
> The whole if !disabled, disable logic is uber paranoid programming, but
> I don't think we've ever seen that WARN trigger, and if it does (and
> then burns the kernel) we at least know wtf happend.

I certainly don't mind personally, as long as we get the warning. Now
I've seen different
 opinions on matters such as this. Some prefer to have the
auto-correction, some don't.

I'll try as you say and see if anybody gets angry :)