[PATCH 0/6] Fixes and cleanups to xarray

[PATCH 0/6] Fixes and cleanups to xarray

[Kemeng Shi]

This series contains some random fixes and cleanups to xarray. Patch 1-3
are fixes and patch 4-6 are cleanups. More details can be found in
respective patches. Thanks!

Kemeng Shi (6):
  Xarray: Do not return sibling entries from xas_find_marked()
  Xarray: distinguish large entries correctly in xas_split_alloc()
  Xarray: move forward index correctly in xas_pause()
  Xarray: skip unneeded xas_store() and xas_clear_mark() in __xa_alloc()
  Xarray: remove repeat check in xas_squash_marks()
  Xarray: use xa_mark_t in xas_squash_marks() to keep code consistent

 lib/test_xarray.c                     | 35 +++++++++++++++++++++++++++
 lib/xarray.c                          | 33 ++++++++++++++-----------
 tools/testing/radix-tree/multiorder.c |  4 +++
 3 files changed, 58 insertions(+), 14 deletions(-)

-- 
2.30.0

[PATCH 1/6] Xarray: Do not return sibling entries from xas_find_marked()

[Kemeng Shi]

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@huaweicloud.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

[PATCH 2/6] Xarray: distinguish large entries correctly in xas_split_alloc()

[Kemeng Shi]

We don't support large entries which expand two more level xa_node in
split. For case "xas->xa_shift + 2 * XA_CHUNK_SHIFT == order", we also
need two level of xa_node to expand. Distinguish entry as large entry in
case "xas->xa_shift + 2 * XA_CHUNK_SHIFT == order".

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
---
 lib/xarray.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/xarray.c b/lib/xarray.c
index fa87949719a0..b9fd321a02ad 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1022,7 +1022,7 @@ void xas_split_alloc(struct xa_state *xas, void *entry, unsigned int order,
 	unsigned int mask = xas->xa_sibs;
 
 	/* XXX: no support for splitting really large entries yet */
-	if (WARN_ON(xas->xa_shift + 2 * XA_CHUNK_SHIFT < order))
+	if (WARN_ON(xas->xa_shift + 2 * XA_CHUNK_SHIFT <= order))
 		goto nomem;
 	if (xas->xa_shift + XA_CHUNK_SHIFT > order)
 		return;
-- 
2.30.0

[PATCH 3/6] Xarray: move forward index correctly in xas_pause()

[Kemeng Shi]

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().

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
---
 lib/test_xarray.c | 35 +++++++++++++++++++++++++++++++++++
 lib/xarray.c      |  1 +
 2 files changed, 36 insertions(+)

diff --git a/lib/test_xarray.c b/lib/test_xarray.c
index d5c5cbba33ed..6932a26f4927 100644
--- a/lib/test_xarray.c
+++ b/lib/test_xarray.c
@@ -1448,6 +1448,41 @@ static noinline void check_pause(struct xarray *xa)
 	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 xarray *xa)
diff --git a/lib/xarray.c b/lib/xarray.c
index b9fd321a02ad..3fac3f2cea9d 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1147,6 +1147,7 @@ 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;
-- 
2.30.0

[PATCH 4/6] Xarray: skip unneeded xas_store() and xas_clear_mark() in __xa_alloc()

[Kemeng Shi]

If xas_find_marked() failed, there is no need to call xas_store() and
xas_clear_mark(). Just call xas_store() and xas_clear_mark() if
xas_find_marked() succeed.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
---
 lib/xarray.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/lib/xarray.c b/lib/xarray.c
index 3fac3f2cea9d..012d0ef5e847 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1860,10 +1860,11 @@ int __xa_alloc(struct xarray *xa, u32 *id, void *entry,
 		xas_find_marked(&xas, limit.max, XA_FREE_MARK);
 		if (xas.xa_node == XAS_RESTART)
 			xas_set_err(&xas, -EBUSY);
-		else
+		else {
 			*id = xas.xa_index;
-		xas_store(&xas, entry);
-		xas_clear_mark(&xas, XA_FREE_MARK);
+			xas_store(&xas, entry);
+			xas_clear_mark(&xas, XA_FREE_MARK);
+		}
 	} while (__xas_nomem(&xas, gfp));
 
 	return xas_error(&xas);
-- 
2.30.0

Re: [PATCH 4/6] Xarray: skip unneeded xas_store() and xas_clear_mark() in __xa_alloc()

[Matthew Wilcox]

On Fri, Nov 01, 2024 at 11:50:26PM +0800, Kemeng Shi wrote:
> If xas_find_marked() failed, there is no need to call xas_store() and
> xas_clear_mark(). Just call xas_store() and xas_clear_mark() if
> xas_find_marked() succeed.

No.  The point of the xas interfaces is that they turn into no-ops once
an error has occurred.

> -		else
> +		else {
>  			*id = xas.xa_index;
> -		xas_store(&xas, entry);
> -		xas_clear_mark(&xas, XA_FREE_MARK);
> +			xas_store(&xas, entry);
> +			xas_clear_mark(&xas, XA_FREE_MARK);
> +		}
>  	} while (__xas_nomem(&xas, gfp));
>  
>  	return xas_error(&xas);
> -- 
> 2.30.0
> 

Re: [PATCH 4/6] Xarray: skip unneeded xas_store() and xas_clear_mark() in __xa_alloc()

[Kemeng Shi]

on 11/2/2024 12:02 AM, Matthew Wilcox wrote:
> On Fri, Nov 01, 2024 at 11:50:26PM +0800, Kemeng Shi wrote:
>> If xas_find_marked() failed, there is no need to call xas_store() and
>> xas_clear_mark(). Just call xas_store() and xas_clear_mark() if
>> xas_find_marked() succeed.
> 
> No.  The point of the xas interfaces is that they turn into no-ops once
> an error has occurred.
Yes, xas interfaces can tolerate error. The question is do we really need to
call xas_store(...) here if we already know there is no room to store new entry.
But no insistant on this as it's not a big deal anyway.

Will drop this on next version if you still disklike this.
Thanks.

> 
>> -		else
>> +		else {
>>  			*id = xas.xa_index;
>> -		xas_store(&xas, entry);
>> -		xas_clear_mark(&xas, XA_FREE_MARK);
>> +			xas_store(&xas, entry);
>> +			xas_clear_mark(&xas, XA_FREE_MARK);
>> +		}
>>  	} while (__xas_nomem(&xas, gfp));
>>  
>>  	return xas_error(&xas);
>> -- 
>> 2.30.0
>>
> 

Re: [PATCH 4/6] Xarray: skip unneeded xas_store() and xas_clear_mark() in __xa_alloc()

[Matthew Wilcox]

On Mon, Nov 04, 2024 at 09:55:42AM +0800, Kemeng Shi wrote:
> > No.  The point of the xas interfaces is that they turn into no-ops once
> > an error has occurred.
> Yes, xas interfaces can tolerate error. The question is do we really need to
> call xas_store(...) here if we already know there is no room to store new entry.
> But no insistant on this as it's not a big deal anyway.
> 
> Will drop this on next version if you still disklike this.

I very much dislike this.  The point is to make the callers simpler.

[PATCH 5/6] Xarray: remove repeat check in xas_squash_marks()

[Kemeng Shi]

Caller of xas_squash_marks() has ensured xas->xa_sibs is non-zero. Just
remove repeat check of xas->xa_sibs in xas_squash_marks().

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
---
 lib/xarray.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/lib/xarray.c b/lib/xarray.c
index 012d0ef5e847..76693aa6cb49 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -128,9 +128,6 @@ static void xas_squash_marks(const struct xa_state *xas)
 	unsigned int mark = 0;
 	unsigned int limit = xas->xa_offset + xas->xa_sibs + 1;
 
-	if (!xas->xa_sibs)
-		return;
-
 	do {
 		unsigned long *marks = xas->xa_node->marks[mark];
 		if (find_next_bit(marks, limit, xas->xa_offset + 1) == limit)
-- 
2.30.0

[PATCH 6/6] Xarray: use xa_mark_t in xas_squash_marks() to keep code consistent

[Kemeng Shi]

Besides xas_squash_marks(), all functions use xa_mark_t type to iterate
all possible marks. Use xa_mark_t in xas_squash_marks() to keep code
consistent.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
---
 lib/xarray.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/lib/xarray.c b/lib/xarray.c
index 76693aa6cb49..6bfc24cac548 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -125,16 +125,20 @@ static inline void node_mark_all(struct xa_node *node, xa_mark_t mark)
  */
 static void xas_squash_marks(const struct xa_state *xas)
 {
-	unsigned int mark = 0;
+	xa_mark_t mark = 0;
 	unsigned int limit = xas->xa_offset + xas->xa_sibs + 1;
 
-	do {
-		unsigned long *marks = xas->xa_node->marks[mark];
-		if (find_next_bit(marks, limit, xas->xa_offset + 1) == limit)
-			continue;
-		__set_bit(xas->xa_offset, marks);
-		bitmap_clear(marks, xas->xa_offset + 1, xas->xa_sibs);
-	} while (mark++ != (__force unsigned)XA_MARK_MAX);
+	for (;;) {
+		unsigned long *marks = node_marks(xas->xa_node, mark);
+
+		if (find_next_bit(marks, limit, xas->xa_offset + 1) != limit) {
+			__set_bit(xas->xa_offset, marks);
+			bitmap_clear(marks, xas->xa_offset + 1, xas->xa_sibs);
+		}
+		if (mark == XA_MARK_MAX)
+			break;
+		mark_inc(mark);
+	}
 }
 
 /* extracts the offset within this node from the index */
-- 
2.30.0