From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
The usage of get_cpu_var() in zs_map_object() is problematic because
it disables preemption and makes it impossible to acquire any sleeping
lock on PREEMPT_RT such as a spinlock_t.
Replace the get_cpu_var() usage with a local_lock_t which is embedded
struct mapping_area. It ensures that the access the struct is
synchronized against all users on the same CPU.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
[minchan: remove the bit_spin_lock part and change the title]
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
mm/zsmalloc.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 5d4c4d254679..7e03cc9363bb 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -65,6 +65,7 @@
#include <linux/wait.h>
#include <linux/pagemap.h>
#include <linux/fs.h>
+#include <linux/local_lock.h>
#define ZSPAGE_MAGIC 0x58
@@ -276,6 +277,7 @@ struct zspage {
};
struct mapping_area {
+ local_lock_t lock;
char *vm_buf; /* copy buffer for objects that span pages */
char *vm_addr; /* address of kmap_atomic()'ed pages */
enum zs_mapmode vm_mm; /* mapping mode */
@@ -451,7 +453,9 @@ MODULE_ALIAS("zpool-zsmalloc");
#endif /* CONFIG_ZPOOL */
/* per-cpu VM mapping areas for zspage accesses that cross page boundaries */
-static DEFINE_PER_CPU(struct mapping_area, zs_map_area);
+static DEFINE_PER_CPU(struct mapping_area, zs_map_area) = {
+ .lock = INIT_LOCAL_LOCK(lock),
+};
static __maybe_unused int is_first_page(struct page *page)
{
@@ -1269,7 +1273,8 @@ void *zs_map_object(struct zs_pool *pool, unsigned long handle,
class = zspage_class(pool, zspage);
off = (class->size * obj_idx) & ~PAGE_MASK;
- area = &get_cpu_var(zs_map_area);
+ local_lock(&zs_map_area.lock);
+ area = this_cpu_ptr(&zs_map_area);
area->vm_mm = mm;
if (off + class->size <= PAGE_SIZE) {
/* this object is contained entirely within a page */
@@ -1320,7 +1325,7 @@ void zs_unmap_object(struct zs_pool *pool, unsigned long handle)
__zs_unmap_object(area, pages, off, class->size);
}
- put_cpu_var(zs_map_area);
+ local_unlock(&zs_map_area.lock);
migrate_read_unlock(zspage);
}
--
2.34.0.rc1.387.gb447b232ab-goog
