Patch "mm: khugepaged: close use-after-free race during shmem collapsing" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

mm: khugepaged: close use-after-free race during shmem collapsing

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-khugepaged-close-use-after-free-race-during-shmem-collapsing.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Johannes Weiner <[email protected]>
Date: Mon, 12 Dec 2016 16:43:32 -0800
Subject: mm: khugepaged: close use-after-free race during shmem collapsing

From: Johannes Weiner <[email protected]>

commit 91a45f71078a6569ec3ca5bef74e1ab58121d80e upstream.

Patch series "mm: workingset: radix tree subtleties & single-page file refaults", v3.

This is another revision of the radix tree / workingset patches based on feedback from Jan and Kirill.

This is a follow-up to d3798ae8c6f3 ("mm: filemap: don't plant shadow entries without radix tree node"). That patch fixed an issue that was caused mainly by the page cache sneaking special shadow page entries into the radix tree and relying on subtleties in the radix tree code to make that work. The fix also had to stop tracking refaults for single-page files because shadow pages stored as direct pointers in radix_tree_root->rnode weren't properly handled during tree extension.

These patches make the radix tree code explicitely support and track such special entries, to eliminate the subtleties and to restore the thrash detection for single-page files.

This patch (of 9):

When a radix tree iteration drops the tree lock, another thread might swoop in and free the node holding the current slot. The iteration needs to do another tree lookup from the current index to continue.

---
 mm/khugepaged.c |    5 +++++
 1 file changed, 5 insertions(+)

@@ -1403,6 +1403,9 @@ static void collapse_shmem(struct mm_str
 
 		spin_lock_irq(&mapping->tree_lock);
 
+		slot = radix_tree_lookup_slot(&mapping->page_tree, index);
+		VM_BUG_ON_PAGE(page != radix_tree_deref_slot_protected(slot,
+					&mapping->tree_lock), page);
 		VM_BUG_ON_PAGE(page_mapped(page), page);
 
 		/*

@@ -1426,6 +1429,7 @@ static void collapse_shmem(struct mm_str
 		radix_tree_replace_slot(slot,
 				new_page + (index % HPAGE_PMD_NR));
 
+		slot = radix_tree_iter_next(&iter);
 		index++;
 		continue;
 out_lru:

@@ -1537,6 +1541,7 @@ tree_unlocked:
 			putback_lru_page(page);
 			unlock_page(page);
 			spin_lock_irq(&mapping->tree_lock);
+			slot = radix_tree_iter_next(&iter);
 		}
 		VM_BUG_ON(nr_none);
 		spin_unlock_irq(&mapping->tree_lock);

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/mm-khugepaged-fix-radix-tree-node-leak-in-shmem-collapse-error-path.patch queue-4.9/mm-khugepaged-close-use-after-free-race-during-shmem-collapsing.patch