4.20-stable review patch. If anyone has any objections, please let me know.
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From: Gao Xiang gaoxiang25@huawei.com
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@huawei.com Signed-off-by: Gao Xiang gaoxiang25@huawei.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- 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 @@ -221,23 +221,29 @@ 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;