4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Gao Xiang <gaoxiang25@xxxxxxxxxx>
commit df134b8d17b90c1e7720e318d36416b57424ff7a upstream.
It's better to use atomic_cond_read_relaxed, which is implemented
in hardware instructions to monitor a variable changes currently
for ARM64, instead of open-coded busy waiting.
Reviewed-by: Chao Yu <yuchao0@xxxxxxxxxx>
Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/staging/erofs/internal.h | 30 ++++++++++++++++++------------
1 file changed, 18 insertions(+), 12 deletions(-)
--- a/drivers/staging/erofs/internal.h
+++ b/drivers/staging/erofs/internal.h
@@ -211,23 +211,29 @@ static inline void erofs_workgroup_unfre
preempt_enable();
}
+#if defined(CONFIG_SMP)
+static inline int erofs_wait_on_workgroup_freezed(struct erofs_workgroup *grp)
+{
+ return atomic_cond_read_relaxed(&grp->refcount,
+ VAL != EROFS_LOCKED_MAGIC);
+}
+#else
+static inline int erofs_wait_on_workgroup_freezed(struct erofs_workgroup *grp)
+{
+ int v = atomic_read(&grp->refcount);
+
+ /* workgroup is never freezed on uniprocessor systems */
+ DBG_BUGON(v == EROFS_LOCKED_MAGIC);
+ return v;
+}
+#endif
+
static inline bool erofs_workgroup_get(struct erofs_workgroup *grp, int *ocnt)
{
- const int locked = (int)EROFS_LOCKED_MAGIC;
int o;
repeat:
- o = atomic_read(&grp->refcount);
-
- /* spin if it is temporarily locked at the reclaim path */
- if (unlikely(o == locked)) {
-#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
- do
- cpu_relax();
- while (atomic_read(&grp->refcount) == locked);
-#endif
- goto repeat;
- }
+ o = erofs_wait_on_workgroup_freezed(grp);
if (unlikely(o <= 0))
return -1;
