linux-kernel - Re: [v2] locking/percpu-rwsem: Optimize readers and reduce global impact

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Message-ID: <e1ad7bcf-4bfd-ac5e-2745-16f9091cb988@roeck-us.net>
Date:   Wed, 31 Aug 2016 06:47:27 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Oleg Nesterov <oleg@...hat.com>,
        John Stultz <john.stultz@...aro.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>, Tejun Heo <tj@...nel.org>,
        Dmitry Shmidt <dimitrysh@...gle.com>,
        Rom Lemarchand <romlem@...gle.com>,
        Colin Cross <ccross@...gle.com>, Todd Kjos <tkjos@...gle.com>
Subject: Re: [v2] locking/percpu-rwsem: Optimize readers and reduce global
 impact

On 08/31/2016 06:41 AM, Guenter Roeck wrote:
> On 08/31/2016 01:09 AM, Peter Zijlstra wrote:
>> On Tue, Aug 30, 2016 at 10:21:02PM -0700, Guenter Roeck wrote:
>>> Peter,
>>>
>>> The call to rcu_sync_is_idle() causes the following build error when building
>>> x86_64:allmodconfig.
>>>
>>> ERROR: "rcu_sync_lockdep_assert" [kernel/locking/locktorture.ko] undefined!
>>> ERROR: "rcu_sync_lockdep_assert" [fs/ext4/ext4.ko] undefined!
>>>
>>> I think this was also reported by the 0-day build bot.
>>>
>>> The simple fix would of course be to export rcu_sync_lockdep_assert. Before I
>>> apply that change to the Android code (where the patch has been aplied and
>>> the problem is seen) - do you by any chance have a better solution in mind ?
>>
>> Nope, that's exactly what Ingo did when he ran into this. If you look at
>> commit 80127a39681b ("locking/percpu-rwsem: Optimize readers and reduce
>> global impact"), you'll notice the last hunk:
>>
> Ah, I missed that, and didn't realize that it is already upstream. Thanks a lot!
>

Wait, it isn't ... I must have fetched a branch with 80127a39681b. Ignore the noise
I am making until after I had another coffee.

Guenter