Re: [PATCH] locking/rwsem: Fix kernel crash when spinning on RWSEM_OWNER_UNKNOWN

[Peter Zijlstra]

On Wed, Jan 15, 2020 at 07:50:55AM +0100, Christoph Hellwig wrote:
> On Tue, Jan 14, 2020 at 02:03:03PM -0500, Waiman Long wrote:
> > The commit 91d2a812dfb9 ("locking/rwsem: Make handoff writer
> > optimistically spin on owner") will allow a recently woken up waiting
> > writer to spin on the owner. Unfortunately, if the owner happens to be
> > RWSEM_OWNER_UNKNOWN, the code will incorrectly spin on it leading to a
> > kernel crash. This is fixed by passing the proper non-spinnable bits
> > to rwsem_spin_on_owner() so that RWSEM_OWNER_UNKNOWN will be treated
> > as a non-spinnable target.
> > 
> > Fixes: 91d2a812dfb9 ("locking/rwsem: Make handoff writer optimistically spin on owner")
> > 
> > Reported-by: Christoph Hellwig <hch@xxxxxx>
> > Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
> 
> This survives all the tests that showed the problems with the original
> code:
> 
> Tested-by: Christoph Hellwig <hch@xxxxxx>

Thanks!