On Sat, Jun 08, 2019 at 01:03:48AM +0530, Souptick Joarder wrote:
> On Thu, May 23, 2019 at 9:05 PM Jason Gunthorpe <jgg@xxxxxxxx> wrote:
> >
> > From: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
> >
> > So we can check locking at runtime.
> >
> > Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
> > mm/hmm.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/hmm.c b/mm/hmm.c
> > index 2695925c0c5927..46872306f922bb 100644
> > +++ b/mm/hmm.c
> > @@ -256,11 +256,11 @@ static const struct mmu_notifier_ops hmm_mmu_notifier_ops = {
> > *
> > * To start mirroring a process address space, the device driver must register
> > * an HMM mirror struct.
> > - *
> > - * THE mm->mmap_sem MUST BE HELD IN WRITE MODE !
> > */
> > int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm)
> > {
> > + lockdep_assert_held_exclusive(mm->mmap_sem);
> > +
>
> Gentle query, does the same required in hmm_mirror_unregister() ?
No.. The unregistration path does its actual work in the srcu
callback, which is in a different context than this function. So any
locking held by the caller of unregister will not apply.
The hmm_range_free SRCU callback obtains the write side of mmap_sem to
protect the same data that the write side above in register is
touching, mostly &mm->hmm.
Jason
