From: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
This function simply creates a slot in the XArray for users which need
to acquire multiple locks before storing their entry in the tree and
so cannot use a plain xa_store().
Signed-off-by: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
---
include/linux/xarray.h | 14 ++++++++++
lib/xarray.c | 51 ++++++++++++++++++++++++++++++++++
tools/testing/radix-tree/xarray-test.c | 25 +++++++++++++++++
3 files changed, 90 insertions(+)
diff --git a/include/linux/xarray.h b/include/linux/xarray.h
index 6f59f1f60205..c3f7405c5517 100644
--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -259,6 +259,7 @@ void *xa_load(struct xarray *, unsigned long index);
void *xa_store(struct xarray *, unsigned long index, void *entry, gfp_t);
void *xa_cmpxchg(struct xarray *, unsigned long index,
void *old, void *entry, gfp_t);
+int xa_reserve(struct xarray *, unsigned long index, gfp_t);
bool xa_get_tag(struct xarray *, unsigned long index, xa_tag_t);
void xa_set_tag(struct xarray *, unsigned long index, xa_tag_t);
void xa_clear_tag(struct xarray *, unsigned long index, xa_tag_t);
@@ -373,6 +374,19 @@ static inline int xa_insert(struct xarray *xa, unsigned long index,
return -EEXIST;
}
+/**
+ * xa_release() - Release a reserved entry.
+ * @xa: XArray.
+ * @index: Index of entry.
+ *
+ * After calling xa_reserve(), you can call this function to release the
+ * reservation. It is harmless to call this function if the entry was used.
+ */
+static inline void xa_release(struct xarray *xa, unsigned long index)
+{
+ xa_cmpxchg(xa, index, NULL, NULL, 0);
+}
+
#define xa_trylock(xa) spin_trylock(&(xa)->xa_lock)
#define xa_lock(xa) spin_lock(&(xa)->xa_lock)
#define xa_unlock(xa) spin_unlock(&(xa)->xa_lock)
diff --git a/lib/xarray.c b/lib/xarray.c
index ace309cc9253..b4dec8e2d202 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1275,6 +1275,8 @@ void *xa_cmpxchg(struct xarray *xa, unsigned long index,
do {
xas_lock(&xas);
curr = xas_load(&xas);
+ if (curr == XA_ZERO_ENTRY)
+ curr = NULL;
if (curr == old)
xas_store(&xas, entry);
xas_unlock(&xas);
@@ -1310,6 +1312,8 @@ void *__xa_cmpxchg(struct xarray *xa, unsigned long index,
do {
curr = xas_load(&xas);
+ if (curr == XA_ZERO_ENTRY)
+ curr = NULL;
if (curr == old)
xas_store(&xas, entry);
} while (__xas_nomem(&xas, gfp));
@@ -1318,6 +1322,53 @@ void *__xa_cmpxchg(struct xarray *xa, unsigned long index,
}
EXPORT_SYMBOL(__xa_cmpxchg);
+/**
+ * xa_reserve() - Reserve this index in the XArray.
+ * @xa: XArray.
+ * @index: Index into array.
+ * @gfp: Memory allocation flags.
+ *
+ * Ensures there is somewhere to store an entry at @index in the array.
+ * If there is already something stored at @index, this function does
+ * nothing. If there was nothing there, the entry is marked as reserved.
+ * Loads from @index will continue to see a %NULL pointer until a
+ * subsequent store to @index.
+ *
+ * If you do not use the entry that you have reserved, call xa_release()
+ * or xa_erase() to free any unnecessary memory.
+ *
+ * Return: 0 if the reservation succeeded or -ENOMEM if it failed.
+ */
+int xa_reserve(struct xarray *xa, unsigned long index, gfp_t gfp)
+{
+ XA_STATE(xas, xa, index);
+ unsigned int lock_type = xa_lock_type(xa);
+ void *curr;
+
+ do {
+ if (lock_type == XA_LOCK_IRQ)
+ xas_lock_irq(&xas);
+ else if (lock_type == XA_LOCK_BH)
+ xas_lock_bh(&xas);
+ else
+ xas_lock(&xas);
+
+ curr = xas_create(&xas);
+ if (!curr)
+ xas_store(&xas, XA_ZERO_ENTRY);
+
+ if (lock_type == XA_LOCK_IRQ)
+ xas_unlock_irq(&xas);
+ else if (lock_type == XA_LOCK_BH)
+ xas_unlock_bh(&xas);
+ else
+ xas_unlock(&xas);
+ } while (xas_nomem(&xas, gfp));
+
+ return xas_error(&xas);
+}
+EXPORT_SYMBOL(xa_reserve);
+
/**
* __xa_set_tag() - Set this tag on this entry while locked.
* @xa: XArray.
diff --git a/tools/testing/radix-tree/xarray-test.c b/tools/testing/radix-tree/xarray-test.c
index 4d3541ac31e9..fe38b53df2ab 100644
--- a/tools/testing/radix-tree/xarray-test.c
+++ b/tools/testing/radix-tree/xarray-test.c
@@ -502,6 +502,29 @@ void check_move(struct xarray *xa)
} while (i < (1 << 16));
}
+void check_reserve(struct xarray *xa)
+{
+ assert(xa_empty(xa));
+ xa_reserve(xa, 12345678, GFP_KERNEL);
+ assert(!xa_empty(xa));
+ assert(!xa_load(xa, 12345678));
+ xa_release(xa, 12345678);
+ assert(xa_empty(xa));
+
+ xa_reserve(xa, 12345678, GFP_KERNEL);
+ assert(!xa_store(xa, 12345678, xa_mk_value(12345678), GFP_NOWAIT));
+ xa_release(xa, 12345678);
+ assert(xa_erase(xa, 12345678) == xa_mk_value(12345678));
+ assert(xa_empty(xa));
+
+ xa_reserve(xa, 12345678, GFP_KERNEL);
+ assert(!xa_cmpxchg(xa, 12345678, NULL, xa_mk_value(12345678),
+ GFP_NOWAIT));
+ xa_release(xa, 12345678);
+ assert(xa_erase(xa, 12345678) == xa_mk_value(12345678));
+ assert(xa_empty(xa));
+}
+
void xarray_checks(void)
{
DEFINE_XARRAY(array);
@@ -548,6 +571,8 @@ void xarray_checks(void)
check_move(&array);
item_kill_tree(&array);
+
+ check_reserve(&array);
}
int __weak main(void)
--
2.15.1
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