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

From: Guenter Roeck
Date: Wed Aug 31 2016 - 09:41:55 EST

On 08/31/2016 01:09 AM, Peter Zijlstra wrote:
On Tue, Aug 30, 2016 at 10:21:02PM -0700, Guenter Roeck wrote:

The call to rcu_sync_is_idle() causes the following build error when building

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!