On Fri, Oct 26, 2018 at 09:49:05AM -0700, Bart Van Assche wrote:
> +++ b/include/linux/rwsem.h
> @@ -41,6 +41,10 @@ struct rw_semaphore {
> #endif
> #ifdef CONFIG_DEBUG_LOCK_ALLOC
> struct lockdep_map dep_map;
> + /*
> + * Number of up_write() calls that must skip rwsem_release().
> + */
> + unsigned nolockdep;
This reads a bit weird. By definition, only one writer is allowed
at a time. And you can't call up_write() before down_write().
So functionally, this is a bool, and the comment should at least
ackowledge that, even if it remains implemented as an unsigned int.
I'd suggest the implementation uses '= 1' and '= 0' rather than ++ and --.
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 1e79fac3186b..2a953d3b7431 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -81,6 +81,7 @@ static inline struct anon_vma *anon_vma_alloc(void)
>
> anon_vma = kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
> if (anon_vma) {
> + init_rwsem(&anon_vma->rwsem);
> atomic_set(&anon_vma->refcount, 1);
> anon_vma->degree = 1; /* Reference for first vma */
> anon_vma->parent = anon_vma;
Why is this needed? The anon_vma_ctor() already calls init_rwsem().
(I suspect this is one of those ctors that isn't actually useful and
should be inlined into anon_vma_alloc())
