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XArray: Fix xa_for_each with a single element at 0

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The following sequence of calls would result in an infinite loop in
xa_find_after():

	xa_store(xa, 0, x, GFP_KERNEL);
	index = 0;
	xa_for_each(xa, entry, index, ULONG_MAX, XA_PRESENT) { }

xa_find_after() was confusing the situation where we found no entry in
the tree with finding a multiorder entry, so it would look for the
successor entry forever.  Just check for this case explicitly.  Includes
a few new checks in the test suite to be sure this doesn't reappear.

Signed-off-by: Matthew Wilcox <willy@infradead.org>
This commit is contained in:
Matthew Wilcox 2018-11-01 16:55:19 -04:00
parent 651022382c
commit 8229706e03
2 changed files with 31 additions and 1 deletions
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2
lib/xarray.c
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@ -1829,6 +1829,8 @@ void *xa_find_after(struct xarray *xa, unsigned long *indexp,
entry = xas_find_marked(&xas, max, filter);
else
entry = xas_find(&xas, max);
if (xas.xa_node == XAS_BOUNDS)
break;
if (xas.xa_shift) {
if (xas.xa_index & ((1UL << xas.xa_shift) - 1))
continue;