[1/2] xarray: extract xa_zero_to_null

Commit Message

Tamir Duberstein Nov. 12, 2024, 7:25 p.m. UTC

Reduce code duplication by extracting a static inline function that
returns its argument if it is non-zero and NULL otherwise.

This changes xas_result to check for errors before checking for zero but
this cannot change the behavior of existing callers:
- __xa_erase: passes the result of xas_store(_, NULL) which cannot fail.
- __xa_store: passes the result of xas_store(_, entry) which may fail.
  xas_store calls xas_create when entry is not NULL which returns NULL
  on error, which is immediately checked. This should not change
  observable behavior.
- __xa_cmpxchg: passes the result of xas_load(_) which might be zero.
  This would previously return NULL regardless of the outcome of
  xas_store but xas_store cannot fail if xas_load returns zero
  because there is no need to allocate memory.
- xa_store_range: same as __xa_erase.

Signed-off-by: Tamir Duberstein <[e-mail]>
---
 lib/xarray.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

Patch

diff --git a/lib/xarray.c b/lib/xarray.c
index 32d4bac8c94ca13e11f350c6bcfcacc2040d0359..1b8305bffbff07adb80334fc83b5dc8e40ba2f50 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -435,6 +435,11 @@  static unsigned long max_index(void *entry)
 	return (XA_CHUNK_SIZE << xa_to_node(entry)->shift) - 1;
 }
 
+static inline void *xa_zero_to_null(void *entry)
+{
+	return xa_is_zero(entry) ? NULL : entry;
+}
+
 static void xas_shrink(struct xa_state *xas)
 {
 	struct xarray *xa = xas->xa;
@@ -451,8 +456,8 @@  static void xas_shrink(struct xa_state *xas)
 			break;
 		if (!xa_is_node(entry) && node->shift)
 			break;
-		if (xa_is_zero(entry) && xa_zero_busy(xa))
-			entry = NULL;
+		if (xa_zero_busy(xa))
+			entry = xa_zero_to_null(entry);
 		xas->xa_node = XAS_BOUNDS;
 
 		RCU_INIT_POINTER(xa->xa_head, entry);
@@ -1474,9 +1479,7 @@  void *xa_load(struct xarray *xa, unsigned long index)
 
 	rcu_read_lock();
 	do {
-		entry = xas_load(&xas);
-		if (xa_is_zero(entry))
-			entry = NULL;
+		entry = xa_zero_to_null(xas_load(&xas));
 	} while (xas_retry(&xas, entry));
 	rcu_read_unlock();
 
@@ -1486,11 +1489,9 @@  EXPORT_SYMBOL(xa_load);
 
 static void *xas_result(struct xa_state *xas, void *curr)
 {
-	if (xa_is_zero(curr))
-		return NULL;
 	if (xas_error(xas))
 		curr = xas->xa_node;
-	return curr;
+	return xa_zero_to_null(curr);
 }
 
 /**