On Wed 13-06-12 22:13:00, Aneesh Kumar K.V wrote:
> Michal Hocko <mhocko@xxxxxxx> writes:
>
> > On Wed 13-06-12 16:59:23, Michal Hocko wrote:
> >> On Wed 13-06-12 15:57:23, Aneesh Kumar K.V wrote:
> >> > From: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
> >> >
> >> > Use a mmu_gather instead of a temporary linked list for accumulating
> >> > pages when we unmap a hugepage range
> >>
> >> Sorry for coming up with the comment that late but you owe us an
> >> explanation _why_ you are doing this.
> >>
> >> I assume that this fixes a real problem when we take i_mmap_mutex
> >> already up in
> >> unmap_mapping_range
> >> mutex_lock(&mapping->i_mmap_mutex);
> >> unmap_mapping_range_tree | unmap_mapping_range_list
> >> unmap_mapping_range_vma
> >> zap_page_range_single
> >> unmap_single_vma
> >> unmap_hugepage_range
> >> mutex_lock(&vma->vm_file->f_mapping->i_mmap_mutex);
> >>
> >> And that this should have been marked for stable as well (I haven't
> >> checked when this has been introduced).
> >>
> >> But then I do not see how this help when you still do this:
> >> [...]
> >> > diff --git a/mm/memory.c b/mm/memory.c
> >> > index 1b7dc66..545e18a 100644
> >> > --- a/mm/memory.c
> >> > +++ b/mm/memory.c
> >> > @@ -1326,8 +1326,11 @@ static void unmap_single_vma(struct mmu_gather *tlb,
> >> > * Since no pte has actually been setup, it is
> >> > * safe to do nothing in this case.
> >> > */
> >> > - if (vma->vm_file)
> >> > - unmap_hugepage_range(vma, start, end, NULL);
> >> > + if (vma->vm_file) {
> >> > + mutex_lock(&vma->vm_file->f_mapping->i_mmap_mutex);
> >> > + __unmap_hugepage_range(tlb, vma, start, end, NULL);
> >> > + mutex_unlock(&vma->vm_file->f_mapping->i_mmap_mutex);
> >> > + }
> >> > } else
> >> > unmap_page_range(tlb, vma, start, end, details);
> >> > }
> >
> > Ahhh, you are removing the lock in the next patch. Really confusing and
> > not nice for the stable backport.
> > Could you merge those two patches and add Cc: stable?
> > Then you can add my
> > Reviewed-by: Michal Hocko <mhocko@xxxxxxx>
> >
>
> In the last review cycle I was asked to see if we can get a lockdep
> report for the above and what I found was we don't really cause the
> above deadlock with the current codebase because for hugetlb we don't
> directly call unmap_mapping_range.
Ahh, ok I missed that.
> But still it is good to remove the i_mmap_mutex, because we don't need
> that protection now. I didn't mark it for stable because of the above
> reason.
Thanks for clarification
>
> -aneesh
>
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxx. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>