linux-kernel - [PATCH 1/6] Xarray: Do not return sibling entries from xas_find

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Message-Id: <20241101155028.11702-2-shikemeng@huaweicloud.com>
Date: Fri,  1 Nov 2024 23:50:23 +0800
From: Kemeng Shi <shikemeng@...weicloud.com>
To: akpm@...ux-foundation.org,
	willy@...radead.org
Cc: linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: [PATCH 1/6] Xarray: Do not return sibling entries from xas_find_marked()

Similar to issue fixed in commit cbc02854331ed ("XArray: Do not return
sibling entries from xa_load()"), we may return sibling entries from
xas_find_marked as following:
    Thread A:               Thread B:
                            xa_store_range(xa, entry, 6, 7, gfp);
			    xa_set_mark(xa, 6, mark)
    XA_STATE(xas, xa, 6);
    xas_find_marked(&xas, 7, mark);
    offset = xas_find_chunk(xas, advance, mark);
    [offset is 6 which points to a valid entry]
                            xa_store_range(xa, entry, 4, 7, gfp);
    entry = xa_entry(xa, node, 6);
    [entry is a sibling of 4]
    if (!xa_is_node(entry))
        return entry;

Skip sibling entry like xas_find() does to protect caller from seeing
sibling entry from xas_find_marked().

Besides, load_race() test is modified to catch mentioned issue and modified
load_race() only passes after this fix is merged.

Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
---
 lib/xarray.c                          | 2 ++
 tools/testing/radix-tree/multiorder.c | 4 ++++
 2 files changed, 6 insertions(+)

diff --git a/lib/xarray.c b/lib/xarray.c
index 32d4bac8c94c..fa87949719a0 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1382,6 +1382,8 @@ void *xas_find_marked(struct xa_state *xas, unsigned long max, xa_mark_t mark)
 		entry = xa_entry(xas->xa, xas->xa_node, xas->xa_offset);
 		if (!entry && !(xa_track_free(xas->xa) && mark == XA_FREE_MARK))
 			continue;
+		if (xa_is_sibling(entry))
+			continue;
 		if (!xa_is_node(entry))
 			return entry;
 		xas->xa_node = xa_to_node(entry);
diff --git a/tools/testing/radix-tree/multiorder.c b/tools/testing/radix-tree/multiorder.c
index cffaf2245d4f..eaff1b036989 100644
--- a/tools/testing/radix-tree/multiorder.c
+++ b/tools/testing/radix-tree/multiorder.c
@@ -227,6 +227,7 @@ static void *load_creator(void *ptr)
 			unsigned long index = (3 << RADIX_TREE_MAP_SHIFT) -
 						(1 << order);
 			item_insert_order(tree, index, order);
+			xa_set_mark(tree, index, XA_MARK_1);
 			item_delete_rcu(tree, index);
 		}
 	}
@@ -242,8 +243,11 @@ static void *load_worker(void *ptr)
 
 	rcu_register_thread();
 	while (!stop_iteration) {
+		unsigned long find_index = (2 << RADIX_TREE_MAP_SHIFT) + 1;
 		struct item *item = xa_load(ptr, index);
 		assert(!xa_is_internal(item));
+		item = xa_find(ptr, &find_index, index, XA_MARK_1);
+		assert(!xa_is_internal(item));
 	}
 	rcu_unregister_thread();
 
-- 
2.30.0