Michal Hocko [off-list ref] writes:

On Wed 13-06-12 16:59:23, Michal Hocko wrote:

quoted

On Wed 13-06-12 15:57:23, Aneesh Kumar K.V wrote:

quoted

From: "Aneesh Kumar K.V" <redacted>

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:
[...]

quoted

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 <redacted>

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. 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.

-aneesh

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