simplify block device claiming (resend)

simplify block device claiming (resend)

[Christoph Hellwig]

Hi Jens,

this series simplifies how we claim block devices for exclusive opens.

Diffstat:
 drivers/block/loop.c   |    7 -
 fs/block_dev.c         |  231 ++++++++++++++++---------------------------------
 include/linux/blkdev.h |    3 
 3 files changed, 81 insertions(+), 160 deletions(-)

[PATCH 1/4] block: simplify the restart case in __blkdev_get

[Christoph Hellwig]

Insted of duplicating all the cleanup logic jump to the code that cleans
up anyway, and restart after that.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/block_dev.c | 25 ++++++++++---------------
 1 file changed, 10 insertions(+), 15 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index a36d5b6907ea4e..376832250c8e91 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1517,7 +1517,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 	int ret;
 	int partno;
 	int perm = 0;
-	bool first_open = false;
+	bool first_open = false, need_restart;
 
 	if (mode & FMODE_READ)
 		perm |= MAY_READ;
@@ -1533,7 +1533,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 	}
 
  restart:
-
+	need_restart = false;
 	ret = -ENXIO;
 	disk = bdev_get_gendisk(bdev, &partno);
 	if (!disk)
@@ -1556,19 +1556,12 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 			ret = 0;
 			if (disk->fops->open) {
 				ret = disk->fops->open(bdev, mode);
-				if (ret == -ERESTARTSYS) {
-					/* Lost a race with 'disk' being
-					 * deleted, try again.
-					 * See md.c
-					 */
-					disk_put_part(bdev->bd_part);
-					bdev->bd_part = NULL;
-					bdev->bd_disk = NULL;
-					mutex_unlock(&bdev->bd_mutex);
-					disk_unblock_events(disk);
-					put_disk_and_module(disk);
-					goto restart;
-				}
+				/*
+				 * If we lost a race with 'disk' being deleted,
+				 * try again.  See md.c
+				 */
+				if (ret == -ERESTARTSYS)
+					need_restart = true;
 			}
 
 			if (!ret) {
@@ -1647,6 +1640,8 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 	mutex_unlock(&bdev->bd_mutex);
 	disk_unblock_events(disk);
 	put_disk_and_module(disk);
+	if (need_restart)
+		goto restart;
  out:
 
 	return ret;
-- 
2.27.0

Re: [PATCH 1/4] block: simplify the restart case in __blkdev_get

[Tejun Heo]

On Thu, Jul 16, 2020 at 04:33:07PM +0200, Christoph Hellwig wrote:
> Insted of duplicating all the cleanup logic jump to the code that cleans
> up anyway, and restart after that.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun

Re: [PATCH 1/4] block: simplify the restart case in __blkdev_get

[Hannes Reinecke]

On 7/16/20 4:33 PM, Christoph Hellwig wrote:
> Insted of duplicating all the cleanup logic jump to the code that cleans
> up anyway, and restart after that.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   fs/block_dev.c | 25 ++++++++++---------------
>   1 file changed, 10 insertions(+), 15 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke            Teamlead Storage & Networking
hare@suse.de                               +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

[PATCH 2/4] block: refactor bd_start_claiming

[Christoph Hellwig]

Move the locking and assignment of bd_claiming from bd_start_claiming to
bd_prepare_to_claim.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/block_dev.c | 33 +++++++++++++--------------------
 1 file changed, 13 insertions(+), 20 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 376832250c8e91..b7b2ee4b288ae9 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1015,19 +1015,14 @@ static bool bd_may_claim(struct block_device *bdev, struct block_device *whole,
 }
 
 /**
- * bd_prepare_to_claim - prepare to claim a block device
+ * bd_prepare_to_claim - claim a block device
  * @bdev: block device of interest
  * @whole: the whole device containing @bdev, may equal @bdev
  * @holder: holder trying to claim @bdev
  *
- * Prepare to claim @bdev.  This function fails if @bdev is already
- * claimed by another holder and waits if another claiming is in
- * progress.  This function doesn't actually claim.  On successful
- * return, the caller has ownership of bd_claiming and bd_holder[s].
- *
- * CONTEXT:
- * spin_lock(&bdev_lock).  Might release bdev_lock, sleep and regrab
- * it multiple times.
+ * Claim @bdev.  This function fails if @bdev is already claimed by another
+ * holder and waits if another claiming is in progress. return, the caller
+ * has ownership of bd_claiming and bd_holder[s].
  *
  * RETURNS:
  * 0 if @bdev can be claimed, -EBUSY otherwise.
@@ -1036,9 +1031,12 @@ static int bd_prepare_to_claim(struct block_device *bdev,
 			       struct block_device *whole, void *holder)
 {
 retry:
+	spin_lock(&bdev_lock);
 	/* if someone else claimed, fail */
-	if (!bd_may_claim(bdev, whole, holder))
+	if (!bd_may_claim(bdev, whole, holder)) {
+		spin_unlock(&bdev_lock);
 		return -EBUSY;
+	}
 
 	/* if claiming is already in progress, wait for it to finish */
 	if (whole->bd_claiming) {
@@ -1049,11 +1047,12 @@ static int bd_prepare_to_claim(struct block_device *bdev,
 		spin_unlock(&bdev_lock);
 		schedule();
 		finish_wait(wq, &wait);
-		spin_lock(&bdev_lock);
 		goto retry;
 	}
 
 	/* yay, all mine */
+	whole->bd_claiming = holder;
+	spin_unlock(&bdev_lock);
 	return 0;
 }
 
@@ -1134,19 +1133,13 @@ struct block_device *bd_start_claiming(struct block_device *bdev, void *holder)
 	if (!whole)
 		return ERR_PTR(-ENOMEM);
 
-	/* prepare to claim, if successful, mark claiming in progress */
-	spin_lock(&bdev_lock);
-
 	err = bd_prepare_to_claim(bdev, whole, holder);
-	if (err == 0) {
-		whole->bd_claiming = holder;
-		spin_unlock(&bdev_lock);
-		return whole;
-	} else {
-		spin_unlock(&bdev_lock);
+	if (err) {
 		bdput(whole);
 		return ERR_PTR(err);
 	}
+
+	return whole;
 }
 EXPORT_SYMBOL(bd_start_claiming);
 
-- 
2.27.0

Re: [PATCH 2/4] block: refactor bd_start_claiming

[Tejun Heo]

On Thu, Jul 16, 2020 at 04:33:08PM +0200, Christoph Hellwig wrote:
> Move the locking and assignment of bd_claiming from bd_start_claiming to
> bd_prepare_to_claim.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun

Re: [PATCH 2/4] block: refactor bd_start_claiming

[Hannes Reinecke]

On 7/16/20 4:33 PM, Christoph Hellwig wrote:
> Move the locking and assignment of bd_claiming from bd_start_claiming to
> bd_prepare_to_claim.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   fs/block_dev.c | 33 +++++++++++++--------------------
>   1 file changed, 13 insertions(+), 20 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke            Teamlead Storage & Networking
hare@suse.de                               +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

[PATCH 3/4] block: use bd_prepare_to_claim directly in the loop driver

[Christoph Hellwig]

The arcane magic in bd_start_claiming is only needed to be able to claim
a block_device that hasn't been fully set up.  Switch the loop driver
that claims from the ioctl path with a fully set up struct block_device
to just use the much simpler bd_prepare_to_claim directly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/loop.c   | 7 +++----
 fs/block_dev.c         | 9 +++++----
 include/linux/blkdev.h | 3 ++-
 3 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index a943207705ddf1..d181601462260b 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1090,11 +1090,10 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
 	 * here to avoid changing device under exclusive owner.
 	 */
 	if (!(mode & FMODE_EXCL)) {
-		claimed_bdev = bd_start_claiming(bdev, loop_configure);
-		if (IS_ERR(claimed_bdev)) {
-			error = PTR_ERR(claimed_bdev);
+		claimed_bdev = bdev->bd_contains;
+		error = bd_prepare_to_claim(bdev, claimed_bdev, loop_configure);
+		if (error)
 			goto out_putf;
-		}
 	}
 
 	error = mutex_lock_killable(&loop_ctl_mutex);
diff --git a/fs/block_dev.c b/fs/block_dev.c
index b7b2ee4b288ae9..ee80bd81af748d 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1027,8 +1027,8 @@ static bool bd_may_claim(struct block_device *bdev, struct block_device *whole,
  * RETURNS:
  * 0 if @bdev can be claimed, -EBUSY otherwise.
  */
-static int bd_prepare_to_claim(struct block_device *bdev,
-			       struct block_device *whole, void *holder)
+int bd_prepare_to_claim(struct block_device *bdev, struct block_device *whole,
+		void *holder)
 {
 retry:
 	spin_lock(&bdev_lock);
@@ -1055,6 +1055,7 @@ static int bd_prepare_to_claim(struct block_device *bdev,
 	spin_unlock(&bdev_lock);
 	return 0;
 }
+EXPORT_SYMBOL_GPL(bd_prepare_to_claim); /* only for the loop driver */
 
 static struct gendisk *bdev_get_gendisk(struct block_device *bdev, int *partno)
 {
@@ -1100,7 +1101,8 @@ static struct gendisk *bdev_get_gendisk(struct block_device *bdev, int *partno)
  * Pointer to the block device containing @bdev on success, ERR_PTR()
  * value on failure.
  */
-struct block_device *bd_start_claiming(struct block_device *bdev, void *holder)
+static struct block_device *bd_start_claiming(struct block_device *bdev,
+		void *holder)
 {
 	struct gendisk *disk;
 	struct block_device *whole;
@@ -1141,7 +1143,6 @@ struct block_device *bd_start_claiming(struct block_device *bdev, void *holder)
 
 	return whole;
 }
-EXPORT_SYMBOL(bd_start_claiming);
 
 static void bd_clear_claiming(struct block_device *whole, void *holder)
 {
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 71173a1ffa8b87..06995b96e94679 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1919,7 +1919,8 @@ int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder);
 struct block_device *blkdev_get_by_path(const char *path, fmode_t mode,
 		void *holder);
 struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder);
-struct block_device *bd_start_claiming(struct block_device *bdev, void *holder);
+int bd_prepare_to_claim(struct block_device *bdev, struct block_device *whole,
+		void *holder);
 void bd_abort_claiming(struct block_device *bdev, struct block_device *whole,
 		void *holder);
 void blkdev_put(struct block_device *bdev, fmode_t mode);
-- 
2.27.0

Re: [PATCH 3/4] block: use bd_prepare_to_claim directly in the loop driver

[Hannes Reinecke]

On 7/16/20 4:33 PM, Christoph Hellwig wrote:
> The arcane magic in bd_start_claiming is only needed to be able to claim
> a block_device that hasn't been fully set up.  Switch the loop driver
> that claims from the ioctl path with a fully set up struct block_device
> to just use the much simpler bd_prepare_to_claim directly.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   drivers/block/loop.c   | 7 +++----
>   fs/block_dev.c         | 9 +++++----
>   include/linux/blkdev.h | 3 ++-
>   3 files changed, 10 insertions(+), 9 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke            Teamlead Storage & Networking
hare@suse.de                               +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

[PATCH 4/4] block: integrate bd_start_claiming into __blkdev_get

[Christoph Hellwig]

bd_start_claiming duplicates a lot of the work done in __blkdev_get.
Integrate the two functions to avoid the duplicate work, and to do the
right thing for the md -ERESTARTSYS corner case.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/block_dev.c | 177 +++++++++++++++----------------------------------
 1 file changed, 55 insertions(+), 122 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index ee80bd81af748d..3f94a06a094675 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1078,72 +1078,6 @@ static struct gendisk *bdev_get_gendisk(struct block_device *bdev, int *partno)
 	return disk;
 }
 
-/**
- * bd_start_claiming - start claiming a block device
- * @bdev: block device of interest
- * @holder: holder trying to claim @bdev
- *
- * @bdev is about to be opened exclusively.  Check @bdev can be opened
- * exclusively and mark that an exclusive open is in progress.  Each
- * successful call to this function must be matched with a call to
- * either bd_finish_claiming() or bd_abort_claiming() (which do not
- * fail).
- *
- * This function is used to gain exclusive access to the block device
- * without actually causing other exclusive open attempts to fail. It
- * should be used when the open sequence itself requires exclusive
- * access but may subsequently fail.
- *
- * CONTEXT:
- * Might sleep.
- *
- * RETURNS:
- * Pointer to the block device containing @bdev on success, ERR_PTR()
- * value on failure.
- */
-static struct block_device *bd_start_claiming(struct block_device *bdev,
-		void *holder)
-{
-	struct gendisk *disk;
-	struct block_device *whole;
-	int partno, err;
-
-	might_sleep();
-
-	/*
-	 * @bdev might not have been initialized properly yet, look up
-	 * and grab the outer block device the hard way.
-	 */
-	disk = bdev_get_gendisk(bdev, &partno);
-	if (!disk)
-		return ERR_PTR(-ENXIO);
-
-	/*
-	 * Normally, @bdev should equal what's returned from bdget_disk()
-	 * if partno is 0; however, some drivers (floppy) use multiple
-	 * bdev's for the same physical device and @bdev may be one of the
-	 * aliases.  Keep @bdev if partno is 0.  This means claimer
-	 * tracking is broken for those devices but it has always been that
-	 * way.
-	 */
-	if (partno)
-		whole = bdget_disk(disk, 0);
-	else
-		whole = bdgrab(bdev);
-
-	put_disk_and_module(disk);
-	if (!whole)
-		return ERR_PTR(-ENOMEM);
-
-	err = bd_prepare_to_claim(bdev, whole, holder);
-	if (err) {
-		bdput(whole);
-		return ERR_PTR(err);
-	}
-
-	return whole;
-}
-
 static void bd_clear_claiming(struct block_device *whole, void *holder)
 {
 	lockdep_assert_held(&bdev_lock);
@@ -1156,7 +1090,7 @@ static void bd_clear_claiming(struct block_device *whole, void *holder)
 /**
  * bd_finish_claiming - finish claiming of a block device
  * @bdev: block device of interest
- * @whole: whole block device (returned from bd_start_claiming())
+ * @whole: whole block device
  * @holder: holder that has claimed @bdev
  *
  * Finish exclusive open of a block device. Mark the device as exlusively
@@ -1182,7 +1116,7 @@ static void bd_finish_claiming(struct block_device *bdev,
 /**
  * bd_abort_claiming - abort claiming of a block device
  * @bdev: block device of interest
- * @whole: whole block device (returned from bd_start_claiming())
+ * @whole: whole block device
  * @holder: holder that has claimed @bdev
  *
  * Abort claiming of a block device when the exclusive open failed. This can be
@@ -1505,13 +1439,15 @@ EXPORT_SYMBOL_GPL(bdev_disk_changed);
  *    mutex_lock_nested(whole->bd_mutex, 1)
  */
 
-static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
+static int __blkdev_get(struct block_device *bdev, fmode_t mode, void *holder,
+		int for_part)
 {
+	struct block_device *whole = NULL, *claiming = NULL;
 	struct gendisk *disk;
 	int ret;
 	int partno;
 	int perm = 0;
-	bool first_open = false, need_restart;
+	bool first_open = false, unblock_events = true, need_restart;
 
 	if (mode & FMODE_READ)
 		perm |= MAY_READ;
@@ -1533,6 +1469,25 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 	if (!disk)
 		goto out;
 
+	if (partno) {
+		whole = bdget_disk(disk, 0);
+		if (!whole) {
+			ret = -ENOMEM;
+			goto out_put_disk;
+		}
+	}
+
+	if (!for_part && (mode & FMODE_EXCL)) {
+		WARN_ON_ONCE(!holder);
+		if (whole)
+			claiming = whole;
+		else
+			claiming = bdev;
+		ret = bd_prepare_to_claim(bdev, claiming, holder);
+		if (ret)
+			goto out_put_whole;
+	}
+
 	disk_block_events(disk);
 	mutex_lock_nested(&bdev->bd_mutex, for_part);
 	if (!bdev->bd_openers) {
@@ -1576,18 +1531,11 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 			if (ret)
 				goto out_clear;
 		} else {
-			struct block_device *whole;
-			whole = bdget_disk(disk, 0);
-			ret = -ENOMEM;
-			if (!whole)
-				goto out_clear;
 			BUG_ON(for_part);
-			ret = __blkdev_get(whole, mode, 1);
-			if (ret) {
-				bdput(whole);
+			ret = __blkdev_get(whole, mode, NULL, 1);
+			if (ret)
 				goto out_clear;
-			}
-			bdev->bd_contains = whole;
+			bdev->bd_contains = bdgrab(whole);
 			bdev->bd_part = disk_get_part(disk, partno);
 			if (!(disk->flags & GENHD_FL_UP) ||
 			    !bdev->bd_part || !bdev->bd_part->nr_sects) {
@@ -1616,11 +1564,30 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 	bdev->bd_openers++;
 	if (for_part)
 		bdev->bd_part_count++;
+	if (claiming)
+		bd_finish_claiming(bdev, claiming, holder);
+
+	/*
+	 * Block event polling for write claims if requested.  Any write holder
+	 * makes the write_holder state stick until all are released.  This is
+	 * good enough and tracking individual writeable reference is too
+	 * fragile given the way @mode is used in blkdev_get/put().
+	 */
+	if (claiming && (mode & FMODE_WRITE) && !bdev->bd_write_holder &&
+	    (disk->flags & GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE)) {
+		bdev->bd_write_holder = true;
+		unblock_events = false;
+	}
 	mutex_unlock(&bdev->bd_mutex);
-	disk_unblock_events(disk);
+
+	if (unblock_events)
+		disk_unblock_events(disk);
+
 	/* only one opener holds refs to the module and disk */
 	if (!first_open)
 		put_disk_and_module(disk);
+	if (whole)
+		bdput(whole);
 	return 0;
 
  out_clear:
@@ -1631,13 +1598,18 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 		__blkdev_put(bdev->bd_contains, mode, 1);
 	bdev->bd_contains = NULL;
  out_unlock_bdev:
+	if (claiming)
+		bd_abort_claiming(bdev, claiming, holder);
 	mutex_unlock(&bdev->bd_mutex);
 	disk_unblock_events(disk);
+ out_put_whole:
+ 	if (whole)
+		bdput(whole);
+ out_put_disk:
 	put_disk_and_module(disk);
 	if (need_restart)
 		goto restart;
  out:
-
 	return ret;
 }
 
@@ -1662,50 +1634,11 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
  */
 int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
 {
-	struct block_device *whole = NULL;
 	int res;
 
-	WARN_ON_ONCE((mode & FMODE_EXCL) && !holder);
-
-	if ((mode & FMODE_EXCL) && holder) {
-		whole = bd_start_claiming(bdev, holder);
-		if (IS_ERR(whole)) {
-			bdput(bdev);
-			return PTR_ERR(whole);
-		}
-	}
-
-	res = __blkdev_get(bdev, mode, 0);
-
-	if (whole) {
-		struct gendisk *disk = whole->bd_disk;
-
-		/* finish claiming */
-		mutex_lock(&bdev->bd_mutex);
-		if (!res)
-			bd_finish_claiming(bdev, whole, holder);
-		else
-			bd_abort_claiming(bdev, whole, holder);
-		/*
-		 * Block event polling for write claims if requested.  Any
-		 * write holder makes the write_holder state stick until
-		 * all are released.  This is good enough and tracking
-		 * individual writeable reference is too fragile given the
-		 * way @mode is used in blkdev_get/put().
-		 */
-		if (!res && (mode & FMODE_WRITE) && !bdev->bd_write_holder &&
-		    (disk->flags & GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE)) {
-			bdev->bd_write_holder = true;
-			disk_block_events(disk);
-		}
-
-		mutex_unlock(&bdev->bd_mutex);
-		bdput(whole);
-	}
-
+	res =__blkdev_get(bdev, mode, holder, 0);
 	if (res)
 		bdput(bdev);
-
 	return res;
 }
 EXPORT_SYMBOL(blkdev_get);
-- 
2.27.0

Re: [PATCH 4/4] block: integrate bd_start_claiming into __blkdev_get

[Tejun Heo]

On Thu, Jul 16, 2020 at 04:33:10PM +0200, Christoph Hellwig wrote:
> bd_start_claiming duplicates a lot of the work done in __blkdev_get.
> Integrate the two functions to avoid the duplicate work, and to do the
> right thing for the md -ERESTARTSYS corner case.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

For 3 and 4,

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun

Re: [PATCH 4/4] block: integrate bd_start_claiming into __blkdev_get

[Hannes Reinecke]

On 7/16/20 4:33 PM, Christoph Hellwig wrote:
> bd_start_claiming duplicates a lot of the work done in __blkdev_get.
> Integrate the two functions to avoid the duplicate work, and to do the
> right thing for the md -ERESTARTSYS corner case.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>   fs/block_dev.c | 177 +++++++++++++++----------------------------------
>   1 file changed, 55 insertions(+), 122 deletions(-)
> 
Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke            Teamlead Storage & Networking
hare@suse.de                               +49 911 74053 688
SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer

Re: simplify block device claiming (resend)

[Jens Axboe]

On 7/16/20 8:33 AM, Christoph Hellwig wrote:
> Hi Jens,
> 
> this series simplifies how we claim block devices for exclusive opens.

Applied, thanks.

-- 
Jens Axboe

simplify block device claiming

[Christoph Hellwig]

Hi Jens,

this series simplifies how we claim block devices for exclusive opens.

Diffstat:
 drivers/block/loop.c   |    7 -
 fs/block_dev.c         |  231 ++++++++++++++++---------------------------------
 include/linux/blkdev.h |    3 
 3 files changed, 81 insertions(+), 160 deletions(-)

[PATCH 3/4] block: use bd_prepare_to_claim directly in the loop driver

[Christoph Hellwig]

The arcane magic in bd_start_claiming is only needed to be able to claim
a block_device that hasn't been fully set up.  Switch the loop driver
that claims from the ioctl path with a fully set up struct block_device
to just use the much simpler bd_prepare_to_claim directly.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/loop.c   | 7 +++----
 fs/block_dev.c         | 9 +++++----
 include/linux/blkdev.h | 3 ++-
 3 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index a943207705ddf1..d181601462260b 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -1090,11 +1090,10 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
 	 * here to avoid changing device under exclusive owner.
 	 */
 	if (!(mode & FMODE_EXCL)) {
-		claimed_bdev = bd_start_claiming(bdev, loop_configure);
-		if (IS_ERR(claimed_bdev)) {
-			error = PTR_ERR(claimed_bdev);
+		claimed_bdev = bdev->bd_contains;
+		error = bd_prepare_to_claim(bdev, claimed_bdev, loop_configure);
+		if (error)
 			goto out_putf;
-		}
 	}
 
 	error = mutex_lock_killable(&loop_ctl_mutex);
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 1c9da1f08011b0..7075004d36997b 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1027,8 +1027,8 @@ static bool bd_may_claim(struct block_device *bdev, struct block_device *whole,
  * RETURNS:
  * 0 if @bdev can be claimed, -EBUSY otherwise.
  */
-static int bd_prepare_to_claim(struct block_device *bdev,
-			       struct block_device *whole, void *holder)
+int bd_prepare_to_claim(struct block_device *bdev, struct block_device *whole,
+		void *holder)
 {
 retry:
 	spin_lock(&bdev_lock);
@@ -1055,6 +1055,7 @@ static int bd_prepare_to_claim(struct block_device *bdev,
 	spin_unlock(&bdev_lock);
 	return 0;
 }
+EXPORT_SYMBOL_GPL(bd_prepare_to_claim); /* only for the loop driver */
 
 static struct gendisk *bdev_get_gendisk(struct block_device *bdev, int *partno)
 {
@@ -1100,7 +1101,8 @@ static struct gendisk *bdev_get_gendisk(struct block_device *bdev, int *partno)
  * Pointer to the block device containing @bdev on success, ERR_PTR()
  * value on failure.
  */
-struct block_device *bd_start_claiming(struct block_device *bdev, void *holder)
+static struct block_device *bd_start_claiming(struct block_device *bdev,
+		void *holder)
 {
 	struct gendisk *disk;
 	struct block_device *whole;
@@ -1141,7 +1143,6 @@ struct block_device *bd_start_claiming(struct block_device *bdev, void *holder)
 
 	return whole;
 }
-EXPORT_SYMBOL(bd_start_claiming);
 
 static void bd_clear_claiming(struct block_device *whole, void *holder)
 {
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 408eb66a82fdc7..6489a0c478165b 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1921,7 +1921,8 @@ int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder);
 struct block_device *blkdev_get_by_path(const char *path, fmode_t mode,
 		void *holder);
 struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder);
-struct block_device *bd_start_claiming(struct block_device *bdev, void *holder);
+int bd_prepare_to_claim(struct block_device *bdev, struct block_device *whole,
+		void *holder);
 void bd_abort_claiming(struct block_device *bdev, struct block_device *whole,
 		void *holder);
 void blkdev_put(struct block_device *bdev, fmode_t mode);
-- 
2.26.2