From: Johannes Weiner <hannes@xxxxxxxxxxx>
Subject: mm: khugepaged: close use-after-free race during shmem collapsing
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.
[kirill.shutemov@xxxxxxxxxxxxxxx: re-lookup for replacement]
Fixes: f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages")
Link: http://lkml.kernel.org/r/20161117191138.22769-2-hannes@xxxxxxxxxxx
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/khugepaged.c | 5 +++++
1 file changed, 5 insertions(+)
diff -puN mm/khugepaged.c~mm-khugepaged-close-use-after-free-race-during-shmem-collapsing mm/khugepaged.c
--- a/mm/khugepaged.c~mm-khugepaged-close-use-after-free-race-during-shmem-collapsing
+++ a/mm/khugepaged.c
@@ -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);
_
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