refactor mddev_find_or_alloc

refactor mddev_find_or_alloc

[Christoph Hellwig]

Hi Song,

this series refactor mddev_find_or_alloc so that is more easier to
read and groups related funtionality into separate helpers.

[PATCH 1/3] md: factor out a mddev_alloc_unit helper from mddev_find

[Christoph Hellwig]

Split out a self contained helper to find a free minor for the md
"unit" number.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/md/md.c | 47 +++++++++++++++++++++++++++--------------------
 1 file changed, 27 insertions(+), 20 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 3ce5f4e0f43180..8ef06330fc66e4 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -745,6 +745,27 @@ static struct mddev *mddev_find_locked(dev_t unit)
 	return NULL;
 }
 
+/* find an unused unit number */
+static dev_t mddev_alloc_unit(void)
+{
+	static int next_minor = 512;
+	int start = next_minor;
+	bool is_free = 0;
+	dev_t dev = 0;
+
+	while (!is_free) {
+		dev = MKDEV(MD_MAJOR, next_minor);
+		next_minor++;
+		if (next_minor > MINORMASK)
+			next_minor = 0;
+		if (next_minor == start)
+			return 0;		/* Oh dear, all in use. */
+		is_free = !mddev_find_locked(dev);
+	}
+
+	return dev;
+}
+
 static struct mddev *mddev_find(dev_t unit)
 {
 	struct mddev *mddev;
@@ -787,27 +808,13 @@ static struct mddev *mddev_find_or_alloc(dev_t unit)
 			return new;
 		}
 	} else if (new) {
-		/* find an unused unit number */
-		static int next_minor = 512;
-		int start = next_minor;
-		int is_free = 0;
-		int dev = 0;
-		while (!is_free) {
-			dev = MKDEV(MD_MAJOR, next_minor);
-			next_minor++;
-			if (next_minor > MINORMASK)
-				next_minor = 0;
-			if (next_minor == start) {
-				/* Oh dear, all in use. */
-				spin_unlock(&all_mddevs_lock);
-				kfree(new);
-				return NULL;
-			}
-
-			is_free = !mddev_find_locked(dev);
+		new->unit = mddev_alloc_unit();
+		if (!new->unit) {
+			spin_unlock(&all_mddevs_lock);
+			kfree(new);
+			return NULL;
 		}
-		new->unit = dev;
-		new->md_minor = MINOR(dev);
+		new->md_minor = MINOR(new->unit);
 		new->hold_active = UNTIL_STOP;
 		list_add(&new->all_mddevs, &all_mddevs);
 		spin_unlock(&all_mddevs_lock);
-- 
2.30.1

[PATCH 2/3] md: refactor mddev_find_or_alloc

[Christoph Hellwig]

Allocate the new mddev first speculatively, which greatly simplifies
the code flow.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/md/md.c | 60 ++++++++++++++++++++-----------------------------
 1 file changed, 24 insertions(+), 36 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 8ef06330fc66e4..de6f8e511c14e7 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -784,57 +784,45 @@ static struct mddev *mddev_find(dev_t unit)
 
 static struct mddev *mddev_find_or_alloc(dev_t unit)
 {
-	struct mddev *mddev, *new = NULL;
+	struct mddev *mddev = NULL, *new;
 
 	if (unit && MAJOR(unit) != MD_MAJOR)
-		unit &= ~((1<<MdpMinorShift)-1);
+		unit &= ~((1 << MdpMinorShift) - 1);
 
- retry:
-	spin_lock(&all_mddevs_lock);
+	new = kzalloc(sizeof(*new), GFP_KERNEL);
+	if (!new)
+		return NULL;
+	mddev_init(new);
 
+	spin_lock(&all_mddevs_lock);
 	if (unit) {
 		mddev = mddev_find_locked(unit);
 		if (mddev) {
 			mddev_get(mddev);
-			spin_unlock(&all_mddevs_lock);
-			kfree(new);
-			return mddev;
+			goto out_free_new;
 		}
 
-		if (new) {
-			list_add(&new->all_mddevs, &all_mddevs);
-			spin_unlock(&all_mddevs_lock);
-			new->hold_active = UNTIL_IOCTL;
-			return new;
-		}
-	} else if (new) {
+		new->unit = unit;
+		if (MAJOR(unit) == MD_MAJOR)
+			new->md_minor = MINOR(unit);
+		else
+			new->md_minor = MINOR(unit) >> MdpMinorShift;
+		new->hold_active = UNTIL_IOCTL;
+	} else {
 		new->unit = mddev_alloc_unit();
-		if (!new->unit) {
-			spin_unlock(&all_mddevs_lock);
-			kfree(new);
-			return NULL;
-		}
+		if (!new->unit)
+			goto out_free_new;
 		new->md_minor = MINOR(new->unit);
 		new->hold_active = UNTIL_STOP;
-		list_add(&new->all_mddevs, &all_mddevs);
-		spin_unlock(&all_mddevs_lock);
-		return new;
 	}
-	spin_unlock(&all_mddevs_lock);
-
-	new = kzalloc(sizeof(*new), GFP_KERNEL);
-	if (!new)
-		return NULL;
 
-	new->unit = unit;
-	if (MAJOR(unit) == MD_MAJOR)
-		new->md_minor = MINOR(unit);
-	else
-		new->md_minor = MINOR(unit) >> MdpMinorShift;
-
-	mddev_init(new);
-
-	goto retry;
+	list_add(&new->all_mddevs, &all_mddevs);
+	spin_unlock(&all_mddevs_lock);
+	return new;
+out_free_new:
+	spin_unlock(&all_mddevs_lock);
+	kfree(new);
+	return mddev;
 }
 
 static struct attribute_group md_redundancy_group;
-- 
2.30.1

[PATCH 3/3] md: do not return existing mddevs from mddev_find_or_alloc

[Christoph Hellwig]

Instead of returning an existing mddev, just for it to be discarded
later directly return -EEXIST.  Rename the function to mddev_alloc now
that it doesn't find an existing mddev.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/md/md.c | 46 +++++++++++++++++++++++-----------------------
 1 file changed, 23 insertions(+), 23 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index de6f8e511c14e7..af9bdb907b2b47 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -782,26 +782,24 @@ static struct mddev *mddev_find(dev_t unit)
 	return mddev;
 }
 
-static struct mddev *mddev_find_or_alloc(dev_t unit)
+static struct mddev *mddev_alloc(dev_t unit)
 {
-	struct mddev *mddev = NULL, *new;
+	struct mddev *new;
+	int error;
 
 	if (unit && MAJOR(unit) != MD_MAJOR)
 		unit &= ~((1 << MdpMinorShift) - 1);
 
 	new = kzalloc(sizeof(*new), GFP_KERNEL);
 	if (!new)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 	mddev_init(new);
 
 	spin_lock(&all_mddevs_lock);
 	if (unit) {
-		mddev = mddev_find_locked(unit);
-		if (mddev) {
-			mddev_get(mddev);
+		error = -EEXIST;
+		if (mddev_find_locked(unit))
 			goto out_free_new;
-		}
-
 		new->unit = unit;
 		if (MAJOR(unit) == MD_MAJOR)
 			new->md_minor = MINOR(unit);
@@ -809,6 +807,7 @@ static struct mddev *mddev_find_or_alloc(dev_t unit)
 			new->md_minor = MINOR(unit) >> MdpMinorShift;
 		new->hold_active = UNTIL_IOCTL;
 	} else {
+		error = -ENODEV;
 		new->unit = mddev_alloc_unit();
 		if (!new->unit)
 			goto out_free_new;
@@ -822,7 +821,7 @@ static struct mddev *mddev_find_or_alloc(dev_t unit)
 out_free_new:
 	spin_unlock(&all_mddevs_lock);
 	kfree(new);
-	return mddev;
+	return ERR_PTR(error);
 }
 
 static struct attribute_group md_redundancy_group;
@@ -5661,29 +5660,29 @@ static int md_alloc(dev_t dev, char *name)
 	 * writing to /sys/module/md_mod/parameters/new_array.
 	 */
 	static DEFINE_MUTEX(disks_mutex);
-	struct mddev *mddev = mddev_find_or_alloc(dev);
+	struct mddev *mddev;
 	struct gendisk *disk;
 	int partitioned;
 	int shift;
 	int unit;
-	int error;
-
-	if (!mddev)
-		return -ENODEV;
+	int error ;
 
-	partitioned = (MAJOR(mddev->unit) != MD_MAJOR);
-	shift = partitioned ? MdpMinorShift : 0;
-	unit = MINOR(mddev->unit) >> shift;
-
-	/* wait for any previous instance of this device to be
-	 * completely removed (mddev_delayed_delete).
+	/*
+	 * Wait for any previous instance of this device to be completely
+	 * removed (mddev_delayed_delete).
 	 */
 	flush_workqueue(md_misc_wq);
 
 	mutex_lock(&disks_mutex);
-	error = -EEXIST;
-	if (mddev->gendisk)
-		goto abort;
+	mddev = mddev_alloc(dev);
+	if (IS_ERR(mddev)) {
+		mutex_unlock(&disks_mutex);
+		return PTR_ERR(mddev);
+	}
+
+	partitioned = (MAJOR(mddev->unit) != MD_MAJOR);
+	shift = partitioned ? MdpMinorShift : 0;
+	unit = MINOR(mddev->unit) >> shift;
 
 	if (name && !dev) {
 		/* Need to ensure that 'name' is not a duplicate.
@@ -5695,6 +5694,7 @@ static int md_alloc(dev_t dev, char *name)
 			if (mddev2->gendisk &&
 			    strcmp(mddev2->gendisk->disk_name, name) == 0) {
 				spin_unlock(&all_mddevs_lock);
+				error = -EEXIST;
 				goto abort;
 			}
 		spin_unlock(&all_mddevs_lock);
-- 
2.30.1

Re: refactor mddev_find_or_alloc

[Song Liu]

On Mon, Apr 12, 2021 at 1:05 AM Christoph Hellwig <hch@lst.de> wrote:
>
>
> Hi Song,
>
> this series refactor mddev_find_or_alloc so that is more easier to
> read and groups related funtionality into separate helpers.

Applied to md-next. Thanks!

Song