On Wed, Jan 30, 2019 at 11:15:30AM +0100, Peter Zijlstra wrote:
> On Tue, Jan 29, 2019 at 08:04:56PM -0800, Alexei Starovoitov wrote:
> > Lockdep warns about false positive:
>
> This is not a false positive, and you probably also need to use
> down_read_non_owner() to match this up_read_non_owner().
>
> {up,down}_read() and {up,down}_read_non_owner() are not only different
> in the lockdep annotation; there is also optimistic spin stuff that
> relies on 'owner' tracking.
Can you point out in the code the spin bit?
As far as I can see sem->owner is debug only feature.
All owner checks are done under CONFIG_DEBUG_RWSEMS.
Also there is no down_read_trylock_non_owner() at the moment.
We can argue about it for -next, but I'd rather silence lockdep
with this patch today.
