[05/11] btrfs: dev-replace: avoid useless lock on error handling path
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Message ID 41a1cc8519061dde7a7cbf2139f672d433a5cfbd.1536331604.git.dsterba@suse.com
State New
Headers show
Series
  • Cleanup dev-replace locking
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Commit Message

David Sterba Sept. 7, 2018, 2:55 p.m. UTC
The exit sequence in btrfs_dev_replace_start does not allow to simply
add a label to the right place so the error handling after starting
transaction failure jumps there. Currently there's a lock that pairs
with the unlock in the section, which is unnecessary and only raises
questions.  Add a variable to track the locking status and avoid the
extra locking.

Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/dev-replace.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

Comments

Omar Sandoval Sept. 7, 2018, 9:06 p.m. UTC | #1
On Fri, Sep 07, 2018 at 04:55:11PM +0200, David Sterba wrote:
> The exit sequence in btrfs_dev_replace_start does not allow to simply
> add a label to the right place so the error handling after starting
> transaction failure jumps there. Currently there's a lock that pairs
> with the unlock in the section, which is unnecessary and only raises
> questions.  Add a variable to track the locking status and avoid the
> extra locking.

Reviewed-by: Omar Sandoval <osandov@fb.com>

> Signed-off-by: David Sterba <dsterba@suse.com>
> ---
>  fs/btrfs/dev-replace.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
> index 8b512dddf727..0a49843b2ee6 100644
> --- a/fs/btrfs/dev-replace.c
> +++ b/fs/btrfs/dev-replace.c
> @@ -400,6 +400,7 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
>  	int ret;
>  	struct btrfs_device *tgt_device = NULL;
>  	struct btrfs_device *src_device = NULL;
> +	bool need_unlock;
>  
>  	ret = btrfs_find_device_by_devspec(fs_info, srcdevid,
>  					    srcdev_name, &src_device);
> @@ -424,6 +425,7 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
>  		return PTR_ERR(trans);
>  	}
>  
> +	need_unlock = true;
>  	btrfs_dev_replace_write_lock(dev_replace);
>  	switch (dev_replace->replace_state) {
>  	case BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED:
> @@ -462,6 +464,7 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
>  	atomic64_set(&dev_replace->num_write_errors, 0);
>  	atomic64_set(&dev_replace->num_uncorrectable_read_errors, 0);
>  	btrfs_dev_replace_write_unlock(dev_replace);
> +	need_unlock = false;
>  
>  	ret = btrfs_sysfs_add_device_link(tgt_device->fs_devices, tgt_device);
>  	if (ret)
> @@ -473,7 +476,6 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
>  	trans = btrfs_start_transaction(root, 0);
>  	if (IS_ERR(trans)) {
>  		ret = PTR_ERR(trans);
> -		btrfs_dev_replace_write_lock(dev_replace);
>  		goto leave;
>  	}
>  
> @@ -497,7 +499,8 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
>  leave:
>  	dev_replace->srcdev = NULL;
>  	dev_replace->tgtdev = NULL;
> -	btrfs_dev_replace_write_unlock(dev_replace);
> +	if (need_unlock)
> +		btrfs_dev_replace_write_unlock(dev_replace);
>  	btrfs_destroy_dev_replace_tgtdev(tgt_device);
>  	return ret;
>  }
> -- 
> 2.18.0
>
David Sterba Sept. 14, 2018, 4:53 p.m. UTC | #2
On Fri, Sep 07, 2018 at 04:55:11PM +0200, David Sterba wrote:
> The exit sequence in btrfs_dev_replace_start does not allow to simply
> add a label to the right place so the error handling after starting
> transaction failure jumps there. Currently there's a lock that pairs
> with the unlock in the section, which is unnecessary and only raises
> questions.  Add a variable to track the locking status and avoid the
> extra locking.
> 
> Signed-off-by: David Sterba <dsterba@suse.com>
> ---
>  fs/btrfs/dev-replace.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
> index 8b512dddf727..0a49843b2ee6 100644
> --- a/fs/btrfs/dev-replace.c
> +++ b/fs/btrfs/dev-replace.c
> @@ -400,6 +400,7 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
>  	int ret;
>  	struct btrfs_device *tgt_device = NULL;
>  	struct btrfs_device *src_device = NULL;
> +	bool need_unlock;
>  
>  	ret = btrfs_find_device_by_devspec(fs_info, srcdevid,
>  					    srcdev_name, &src_device);
> @@ -424,6 +425,7 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
>  		return PTR_ERR(trans);
>  	}
>  
> +	need_unlock = true;
>  	btrfs_dev_replace_write_lock(dev_replace);
>  	switch (dev_replace->replace_state) {
>  	case BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED:
> @@ -462,6 +464,7 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
>  	atomic64_set(&dev_replace->num_write_errors, 0);
>  	atomic64_set(&dev_replace->num_uncorrectable_read_errors, 0);
>  	btrfs_dev_replace_write_unlock(dev_replace);
> +	need_unlock = false;
>  
>  	ret = btrfs_sysfs_add_device_link(tgt_device->fs_devices, tgt_device);
>  	if (ret)
> @@ -473,7 +476,6 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
>  	trans = btrfs_start_transaction(root, 0);
>  	if (IS_ERR(trans)) {
>  		ret = PTR_ERR(trans);
> -		btrfs_dev_replace_write_lock(dev_replace);

There's a merge conflict with Jeff's patch
https://patchwork.kernel.org/patch/10591003/ that adds some dev-replace
state change, so the lock must be here. I'll update my patch to

@@ -474,6 +477,7 @@ int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
        trans = btrfs_start_transaction(root, 0);
        if (IS_ERR(trans)) {
                ret = PTR_ERR(trans);
+               need_unlock = true;
                btrfs_dev_replace_write_lock(dev_replace);
                dev_replace->replace_state =
                        BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED;
---

Patch
diff mbox series

diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c
index 8b512dddf727..0a49843b2ee6 100644
--- a/fs/btrfs/dev-replace.c
+++ b/fs/btrfs/dev-replace.c
@@ -400,6 +400,7 @@  int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
 	int ret;
 	struct btrfs_device *tgt_device = NULL;
 	struct btrfs_device *src_device = NULL;
+	bool need_unlock;
 
 	ret = btrfs_find_device_by_devspec(fs_info, srcdevid,
 					    srcdev_name, &src_device);
@@ -424,6 +425,7 @@  int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
 		return PTR_ERR(trans);
 	}
 
+	need_unlock = true;
 	btrfs_dev_replace_write_lock(dev_replace);
 	switch (dev_replace->replace_state) {
 	case BTRFS_IOCTL_DEV_REPLACE_STATE_NEVER_STARTED:
@@ -462,6 +464,7 @@  int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
 	atomic64_set(&dev_replace->num_write_errors, 0);
 	atomic64_set(&dev_replace->num_uncorrectable_read_errors, 0);
 	btrfs_dev_replace_write_unlock(dev_replace);
+	need_unlock = false;
 
 	ret = btrfs_sysfs_add_device_link(tgt_device->fs_devices, tgt_device);
 	if (ret)
@@ -473,7 +476,6 @@  int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
 	trans = btrfs_start_transaction(root, 0);
 	if (IS_ERR(trans)) {
 		ret = PTR_ERR(trans);
-		btrfs_dev_replace_write_lock(dev_replace);
 		goto leave;
 	}
 
@@ -497,7 +499,8 @@  int btrfs_dev_replace_start(struct btrfs_fs_info *fs_info,
 leave:
 	dev_replace->srcdev = NULL;
 	dev_replace->tgtdev = NULL;
-	btrfs_dev_replace_write_unlock(dev_replace);
+	if (need_unlock)
+		btrfs_dev_replace_write_unlock(dev_replace);
 	btrfs_destroy_dev_replace_tgtdev(tgt_device);
 	return ret;
 }