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SubjectRe: kernel BUG at mm/shmem.c:LINE!
On Mon, Jul 23, 2018 at 03:42:22PM -0700, Hugh Dickins wrote:
> On Mon, 23 Jul 2018, Matthew Wilcox wrote:
> > I figured out a fix and pushed it to the 'ida' branch in
> > git://git.infradead.org/users/willy/linux-dax.git
>
> Great, thanks a lot for sorting that out so quickly. But I've cloned
> the tree and don't see today's patch, so assume you've folded the fix
> into an existing commit? If possible, please append the diff of today's
> fix to this thread so that we can try it out. Or if that's difficult,
> please at least tell which files were modified, then I can probably
> work it out from the diff of those files against mmotm.

Sure! It's just this:

diff --git a/lib/xarray.c b/lib/xarray.c
index 32a9c2a6a9e9..383c410997eb 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -660,6 +660,8 @@ void xas_create_range(struct xa_state *xas)
unsigned char sibs = xas->xa_sibs;

xas->xa_index |= ((sibs + 1) << shift) - 1;
+ if (!xas_top(xas->xa_node) && xas->xa_node->shift == xas->xa_shift)
+ xas->xa_offset |= sibs;
xas->xa_shift = 0;
xas->xa_sibs = 0;

The only other things changed are the test suite, and removing an
unnecessary change, so they can be ignored:

diff --git a/lib/test_xarray.c b/lib/test_xarray.c
index 8a67d4bb1788..ec06c3ca19e9 100644
--- a/lib/test_xarray.c
+++ b/lib/test_xarray.c
@@ -695,19 +695,20 @@ static noinline void check_move(struct xarray *xa)
check_move_small(xa, (1UL << i) - 1);
}

-static noinline void check_create_range_1(struct xarray *xa,
+static noinline void xa_store_many_order(struct xarray *xa,
unsigned long index, unsigned order)
{
XA_STATE_ORDER(xas, xa, index, order);
- unsigned int i;
+ unsigned int i = 0;

do {
xas_lock(&xas);
+ XA_BUG_ON(xa, xas_find_conflict(&xas));
xas_create_range(&xas);
if (xas_error(&xas))
goto unlock;
for (i = 0; i < (1U << order); i++) {
- xas_store(&xas, xa + i);
+ XA_BUG_ON(xa, xas_store(&xas, xa_mk_value(index + i)));
xas_next(&xas);
}
unlock:
@@ -715,7 +716,29 @@ static noinline void check_create_range_1(struct xarray *xa,
} while (xas_nomem(&xas, GFP_KERNEL));

XA_BUG_ON(xa, xas_error(&xas));
- xa_destroy(xa);
+}
+
+static noinline void check_create_range_1(struct xarray *xa,
+ unsigned long index, unsigned order)
+{
+ unsigned long i;
+
+ xa_store_many_order(xa, index, order);
+ for (i = index; i < index + (1UL << order); i++)
+ xa_erase_value(xa, i);
+ XA_BUG_ON(xa, !xa_empty(xa));
+}
+
+static noinline void check_create_range_2(struct xarray *xa, unsigned order)
+{
+ unsigned long i;
+ unsigned long nr = 1UL << order;
+
+ for (i = 0; i < nr * nr; i += nr)
+ xa_store_many_order(xa, i, order);
+ for (i = 0; i < nr * nr; i++)
+ xa_erase_value(xa, i);
+ XA_BUG_ON(xa, !xa_empty(xa));
}

static noinline void check_create_range(struct xarray *xa)
@@ -729,6 +752,8 @@ static noinline void check_create_range(struct xarray *xa)
check_create_range_1(xa, 2U << order, order);
check_create_range_1(xa, 3U << order, order);
check_create_range_1(xa, 1U << 24, order);
+ if (order < 10)
+ check_create_range_2(xa, order);
}
}

diff --git a/mm/shmem.c b/mm/shmem.c
index af2d7fa05af7..3ac507803787 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -589,8 +589,8 @@ static int shmem_add_to_page_cache(struct page *page,
VM_BUG_ON(expected && PageTransHuge(page));

page_ref_add(page, nr);
- page->index = index;
page->mapping = mapping;
+ page->index = index;

do {
void *entry;
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