XArray: Fix xa_release in allocating arrays
xa_cmpxchg() was a little too magic in turning ZERO entries into NULL,
and would leave the entry set to the ZERO entry instead of releasing
it for future use. After careful review of existing users of
xa_cmpxchg(), change the semantics so that it does not translate either
incoming argument from NULL into ZERO entries.
Add several tests to the test-suite to make sure this problem doesn't
come back.
Reported-by: Jason Gunthorpe <jgg@ziepe.ca>
Signed-off-by: Matthew Wilcox <willy@infradead.org>
diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index 687c150..588733a 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -131,6 +131,12 @@
* xa_mk_internal() - Create an internal entry.
* @v: Value to turn into an internal entry.
*
+ * Internal entries are used for a number of purposes. Entries 0-255 are
+ * used for sibling entries (only 0-62 are used by the current code). 256
+ * is used for the retry entry. 257 is used for the reserved / zero entry.
+ * Negative internal entries are used to represent errnos. Node pointers
+ * are also tagged as internal entries in some situations.
+ *
* Context: Any context.
* Return: An XArray internal entry corresponding to this value.
*/
@@ -163,6 +169,22 @@
return ((unsigned long)entry & 3) == 2;
}
+#define XA_ZERO_ENTRY xa_mk_internal(257)
+
+/**
+ * xa_is_zero() - Is the entry a zero entry?
+ * @entry: Entry retrieved from the XArray
+ *
+ * The normal API will return NULL as the contents of a slot containing
+ * a zero entry. You can only see zero entries by using the advanced API.
+ *
+ * Return: %true if the entry is a zero entry.
+ */
+static inline bool xa_is_zero(const void *entry)
+{
+ return unlikely(entry == XA_ZERO_ENTRY);
+}
+
/**
* xa_is_err() - Report whether an XArray operation returned an error
* @entry: Result from calling an XArray function
@@ -1050,7 +1072,7 @@
*/
static inline void xa_release(struct xarray *xa, unsigned long index)
{
- xa_cmpxchg(xa, index, NULL, NULL, 0);
+ xa_cmpxchg(xa, index, XA_ZERO_ENTRY, NULL, 0);
}
/* Everything below here is the Advanced API. Proceed with caution. */
@@ -1210,18 +1232,6 @@
}
#define XA_RETRY_ENTRY xa_mk_internal(256)
-#define XA_ZERO_ENTRY xa_mk_internal(257)
-
-/**
- * xa_is_zero() - Is the entry a zero entry?
- * @entry: Entry retrieved from the XArray
- *
- * Return: %true if the entry is a zero entry.
- */
-static inline bool xa_is_zero(const void *entry)
-{
- return unlikely(entry == XA_ZERO_ENTRY);
-}
/**
* xa_is_retry() - Is the entry a retry entry?