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From: Gao Xiang <gaoxiang25@huawei.com>
To: <stable@vger.kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Chao Yu <yuchao0@huawei.com>, <linux-erofs@lists.ozlabs.org>,
	<miaoxie@huawei.com>, Gao Xiang <gaoxiang25@huawei.com>
Subject: [PATCH for-4.19 07/12] staging: erofs: atomic_cond_read_relaxed on ref-locked workgroup
Date: Wed, 20 Feb 2019 17:18:49 +0800	[thread overview]
Message-ID: <20190220091854.19242-8-gaoxiang25@huawei.com> (raw)
In-Reply-To: <20190220091854.19242-1-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>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
---
 drivers/staging/erofs/internal.h | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/drivers/staging/erofs/internal.h b/drivers/staging/erofs/internal.h
index 122ea5016f3b..0fff0d30fed7 100644
--- a/drivers/staging/erofs/internal.h
+++ b/drivers/staging/erofs/internal.h
@@ -211,23 +211,29 @@ static inline void erofs_workgroup_unfreeze(
 	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;
-- 
2.14.4


WARNING: multiple messages have this Message-ID (diff)
From: gaoxiang25@huawei.com (Gao Xiang)
Subject: [PATCH for-4.19 07/12] staging: erofs: atomic_cond_read_relaxed on ref-locked workgroup
Date: Wed, 20 Feb 2019 17:18:49 +0800	[thread overview]
Message-ID: <20190220091854.19242-8-gaoxiang25@huawei.com> (raw)
In-Reply-To: <20190220091854.19242-1-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 at huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25 at huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
Signed-off-by: Gao Xiang <gaoxiang25 at huawei.com>
---
 drivers/staging/erofs/internal.h | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/drivers/staging/erofs/internal.h b/drivers/staging/erofs/internal.h
index 122ea5016f3b..0fff0d30fed7 100644
--- a/drivers/staging/erofs/internal.h
+++ b/drivers/staging/erofs/internal.h
@@ -211,23 +211,29 @@ static inline void erofs_workgroup_unfreeze(
 	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;
-- 
2.14.4

  parent reply	other threads:[~2019-02-20  9:21 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-20  9:18 [PATCH for-4.19 00/12] erofs fixes for linux-4.19.y Gao Xiang
2019-02-20  9:18 ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 01/12] staging: erofs: fix a bug when appling cache strategy Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 02/12] staging: erofs: complete error handing of z_erofs_do_read_page Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-25 14:59   ` Greg Kroah-Hartman
2019-02-25 14:59     ` Greg Kroah-Hartman
2019-02-25 15:04     ` Gao Xiang
2019-02-25 15:04       ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 03/12] staging: erofs: replace BUG_ON with DBG_BUGON in data.c Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 04/12] staging: erofs: drop multiref support temporarily Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 05/12] staging: erofs: remove the redundant d_rehash() for the root dentry Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 06/12] staging: erofs: fix race when the managed cache is enabled Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-25 15:04   ` Greg Kroah-Hartman
2019-02-25 15:04     ` Greg Kroah-Hartman
2019-02-25 15:07     ` Gao Xiang
2019-02-25 15:07       ` Gao Xiang
2019-02-25 15:51       ` Greg Kroah-Hartman
2019-02-25 15:51         ` Greg Kroah-Hartman
2019-02-25 15:57         ` Gao Xiang
2019-02-25 15:57           ` Gao Xiang
2019-02-25 17:58         ` [PATCH for-4.19 1/2] xarray: Replace exceptional entries Gao Xiang
2019-02-25 17:58           ` Gao Xiang
2019-02-25 17:58           ` [PATCH for-4.19 2/2] staging: erofs: fix race when the managed cache is enabled Gao Xiang
2019-02-25 17:58             ` Gao Xiang
2019-02-25 18:27           ` [PATCH for-4.19 1/2] xarray: Replace exceptional entries Matthew Wilcox
2019-02-25 18:27             ` Matthew Wilcox
2019-02-26  1:21             ` Gao Xiang
2019-02-26  1:21               ` Gao Xiang
2019-02-26  5:14             ` [PATCH v2 " Gao Xiang
2019-02-26  5:14               ` Gao Xiang
2019-02-26  5:14               ` [PATCH v2 for-4.19 2/2] staging: erofs: fix race when the managed cache is enabled Gao Xiang
2019-02-26  5:14                 ` Gao Xiang
2019-02-26 12:43               ` [PATCH v2 for-4.19 1/2] xarray: Replace exceptional entries Gao Xiang
2019-02-26 12:43                 ` Gao Xiang
2019-03-04  5:13                 ` Gao Xiang
2019-03-04  5:13                   ` Gao Xiang
2019-03-13  9:18                   ` Gao Xiang
2019-03-13  9:18                     ` Gao Xiang
2019-02-25 15:25     ` [PATCH for-4.19 06/12] staging: erofs: fix race when the managed cache is enabled Matthew Wilcox
2019-02-25 15:25       ` Matthew Wilcox
2019-02-25 15:52       ` Greg Kroah-Hartman
2019-02-25 15:52         ` Greg Kroah-Hartman
2019-02-25 16:04         ` Matthew Wilcox
2019-02-25 16:04           ` Matthew Wilcox
2019-02-20  9:18 ` Gao Xiang [this message]
2019-02-20  9:18   ` [PATCH for-4.19 07/12] staging: erofs: atomic_cond_read_relaxed on ref-locked workgroup Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 08/12] staging: erofs: fix `erofs_workgroup_{try_to_freeze, unfreeze}' Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 09/12] staging: erofs: add a full barrier in erofs_workgroup_unfreeze Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 10/12] staging: erofs: {dir,inode,super}.c: rectify BUG_ONs Gao Xiang
2019-02-20  9:18   ` [PATCH for-4.19 10/12] staging: erofs: {dir, inode, super}.c: " Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 11/12] staging: erofs: unzip_{pagevec.h,vle.c}: " Gao Xiang
2019-02-20  9:18   ` [PATCH for-4.19 11/12] staging: erofs: unzip_{pagevec.h, vle.c}: " Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 12/12] staging: erofs: unzip_vle_lz4.c,utils.c: " Gao Xiang
2019-02-20  9:18   ` [PATCH for-4.19 12/12] staging: erofs: unzip_vle_lz4.c, utils.c: " Gao Xiang
2019-02-22  8:35 ` [PATCH for-4.19 00/12] erofs fixes for linux-4.19.y Greg Kroah-Hartman
2019-02-22  8:35   ` Greg Kroah-Hartman
2019-02-22  9:03   ` Gao Xiang
2019-02-22  9:03     ` Gao Xiang
2019-02-25 15:28 ` Greg Kroah-Hartman
2019-02-25 15:28   ` Greg Kroah-Hartman

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