[Intel-gfx] [PATCH] drm/i915/userptr: restore probe_range behaviour

[Matthew Wilcox]

On Tue, Oct 25, 2022 at 04:40:23PM +0100, Tvrtko Ursulin wrote:
> 
> On 24/10/2022 18:21, Matthew Auld wrote:
> > The conversion looks harmless, however the addr value is updated inside
> > the loop with the previous vm_end, which then incorrectly leads to
> > for_each_vma_range() iterating over stuff outside the range we care
> > about. Fix this by storing the end value separately.
> > 
> > Testcase: igt at gem_userptr_blits@probe
> > Fixes: f683b9d61319 ("i915: use the VMA iterator")
> > Reported-by: kernel test robot <oliver.sang at intel.com>
> > Signed-off-by: Matthew Auld <matthew.auld at intel.com>
> > Cc: Tvrtko Ursulin <tvrtko.ursulin at linux.intel.com>
> > Cc: Matthew Wilcox (Oracle) <willy at infradead.org>
> > Cc: Vlastimil Babka <vbabka at suse.cz>
> > Cc: Yu Zhao <yuzhao at google.com>
> > ---
> >   drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> > index b7e24476a0fd..dadb3e3fa9c8 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
> > @@ -427,9 +427,10 @@ probe_range(struct mm_struct *mm, unsigned long addr, unsigned long len)
> >   {
> >   	VMA_ITERATOR(vmi, mm, addr);
> >   	struct vm_area_struct *vma;
> > +	unsigned long end = addr + len;
> >   	mmap_read_lock(mm);
> > -	for_each_vma_range(vmi, vma, addr + len) {
> > +	for_each_vma_range(vmi, vma, end) {
> >   		/* Check for holes, note that we also update the addr below */
> >   		if (vma->vm_start > addr)
> >   			break;
> 
> I am unsure of the for_each_vma_range() behaviour regarding holes. If it
> just skips overs them and continues to next VMA in the range then patch
> looks good to me. Could someone confirm?

It's "For each VMA in this range".  It doesn't iterate over non-VMAs
within that range ;-)  Nor does a gap between VMAs stop the iteration.