Re: [PATCH 1/8] mmap locking API: initial implementation as rwsem wrappers

[Matthew Wilcox]

On Thu, Mar 26, 2020 at 02:56:44PM -0300, Jason Gunthorpe wrote:
> On Thu, Mar 26, 2020 at 12:02:29AM -0700, Michel Lespinasse wrote:
> 
> > +static inline bool mmap_is_locked(struct mm_struct *mm)
> > +{
> > +	return rwsem_is_locked(&mm->mmap_sem) != 0;
> > +}
> 
> I've been wondering if the various VM_BUG(rwsem_is_locked()) would be
> better as lockdep expressions? Certainly when lockdep is enabled it
> should be preferred, IMHO.
> 
> So, I think if inlines are to be introduced this should be something
> similar to netdev's ASSERT_RTNL which seems to have worked well.
> 
> Maybe ASSERT_MMAP_SEM_READ/WRITE/HELD() and do the VM_BUG or
> lockdep_is_held as appropriate?

I'd rather see lockdep_assert_held() used directly rather than have
a wrapper.  This API includes options to check for it beind explicitly
held for read/write/any, which should be useful.