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Xarray: move forward index correctly in xas_pause()

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After xas_load(), xas->index could point to mid of found multi-index entry
and xas->index's bits under node->shift maybe non-zero.  The afterward
xas_pause() will move forward xas->index with xa->node->shift with bits
under node->shift un-masked and thus skip some index unexpectedly.

Consider following case:
Assume XA_CHUNK_SHIFT is 4.
xa_store_range(xa, 16, 31, ...)
xa_store(xa, 32, ...)
XA_STATE(xas, xa, 17);
xas_for_each(&xas,...)
xas_load(&xas)
/* xas->index = 17, xas->xa_offset = 1, xas->xa_node->xa_shift = 4 */
xas_pause()
/* xas->index = 33, xas->xa_offset = 2, xas->xa_node->xa_shift = 4 */
As we can see, index of 32 is skipped unexpectedly.

Fix this by mask bit under node->xa_shift when move forward index in
xas_pause().

For now, this will not cause serious problems.  Only minor problem like
cachestat return less number of page status could happen.

Link: https://lkml.kernel.org/r/20241213122523.12764-3-shikemeng@huaweicloud.com
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Mattew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Kemeng Shi 2024-12-13 20:25:20 +08:00 committed by Andrew Morton
parent 7e060df04f
commit c9ba5249ef
2 changed files with 36 additions and 0 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

35
lib/test_xarray.c
View file

@ -1511,6 +1511,41 @@ static noinline void check_pause(struct kunit *test)
XA_BUG_ON(xa, count != order_limit);
xa_destroy(xa);
index = 0;
for (order = XA_CHUNK_SHIFT; order > 0; order--) {
XA_BUG_ON(xa, xa_store_order(xa, index, order,
xa_mk_index(index), GFP_KERNEL));
index += 1UL << order;
}
index = 0;
count = 0;
xas_set(&xas, 0);
rcu_read_lock();
xas_for_each(&xas, entry, ULONG_MAX) {
XA_BUG_ON(xa, entry != xa_mk_index(index));
index += 1UL << (XA_CHUNK_SHIFT - count);
count++;
}
rcu_read_unlock();
XA_BUG_ON(xa, count != XA_CHUNK_SHIFT);
index = 0;
count = 0;
xas_set(&xas, XA_CHUNK_SIZE / 2 + 1);
rcu_read_lock();
xas_for_each(&xas, entry, ULONG_MAX) {
XA_BUG_ON(xa, entry != xa_mk_index(index));
index += 1UL << (XA_CHUNK_SHIFT - count);
count++;
xas_pause(&xas);
}
rcu_read_unlock();
XA_BUG_ON(xa, count != XA_CHUNK_SHIFT);
xa_destroy(xa);
}
static noinline void check_move_tiny(struct kunit *test)

1
lib/xarray.c
View file

@ -1152,6 +1152,7 @@ void xas_pause(struct xa_state *xas)
if (!xa_is_sibling(xa_entry(xas->xa, node, offset)))
break;
}
xas->xa_index &= ~0UL << node->shift;
xas->xa_index += (offset - xas->xa_offset) << node->shift;
if (xas->xa_index == 0)
xas->xa_node = XAS_BOUNDS;