Re: [PATCH 05/11] btrfs: btrfs_init_devices_late: use sprout device_list_mutex

[Nikolay Borisov <nborisov@suse.com>]

On 30.08.20 г. 17:41 ч., Anand Jain wrote:
> In a mounted sprout FS, all threads now are using the
> sprout::device_list_mutex, and this is the only piece of code using
> the seed::device_list_mutex. This patch converts to use the sprouts
> fs_info->fs_devices->device_list_mutex.
> 
> The same reasoning holds true here, that device delete is holding
> the sprout::device_list_mutex.
> 
> Signed-off-by: Anand Jain <anand.jain@oracle.com>
> ---
>  fs/btrfs/volumes.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 9921b43ef839..7639a048c6cf 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -7184,16 +7184,14 @@ void btrfs_init_devices_late(struct btrfs_fs_info *fs_info)
>  	mutex_lock(&fs_devices->device_list_mutex);
>  	list_for_each_entry(device, &fs_devices->devices, dev_list)
>  		device->fs_info = fs_info;
> -	mutex_unlock(&fs_devices->device_list_mutex);
>  
>  	list_for_each_entry(seed_devs, &fs_devices->seed_list, seed_list) {
> -		mutex_lock(&seed_devs->device_list_mutex);
>  		list_for_each_entry(device, &seed_devs->devices, dev_list)
>  			device->fs_info = fs_info;
> -		mutex_unlock(&seed_devs->device_list_mutex);
>  
>  		seed_devs->fs_info = fs_info;
>  	}
> +	mutex_unlock(&fs_devices->device_list_mutex);

Instead of doing the looping here to set fs_info I think it makes more
sense to move the initialization of fs_info for the seed fs_info/seed
devices to open_seed_devices.

As a matter of fact at the point where btrfs_init_devices_late is called
btrfs_read_chunk_tree would have already been called which would have
resulted in all present seed devices be added to fs_info::seed_list. So
acquiring the lock here serves no purpose really.

>  }
>  
>  static u64 btrfs_dev_stats_value(const struct extent_buffer *eb,
>