Re: [PATCH v2 1/2] btrfs: Implement DRW lock

[Nikolay Borisov <nborisov@suse.com>]

On 30.01.20 г. 14:59 ч., Nikolay Borisov wrote:
> A (D)ouble (R)eader (W)riter lock is a locking primitive that allows
> to have multiple readers or multiple writers but not multiple readers
> and writers holding it concurrently. The code is factored out from
> the existing open-coded locking scheme used to exclude pending
> snapshots from nocow writers and vice-versa. Current implementation
> actually favors Readers (that is snapshot creaters) to writers (nocow
> writers of the filesystem).
> 
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
>  fs/btrfs/ctree.h   |  1 +
>  fs/btrfs/locking.c | 87 ++++++++++++++++++++++++++++++++++++++++++++++
>  fs/btrfs/locking.h | 21 +++++++++++
>  3 files changed, 109 insertions(+)
> 
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index f90b82050d2d..908430f563fa 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -33,6 +33,7 @@
>  #include "extent_map.h"
>  #include "async-thread.h"
>  #include "block-rsv.h"
> +#include "locking.h"
>  
>  struct btrfs_trans_handle;
>  struct btrfs_transaction;
> diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c
> index 571c4826c428..66d7d1279535 100644
> --- a/fs/btrfs/locking.c
> +++ b/fs/btrfs/locking.c
> @@ -523,3 +523,90 @@ void btrfs_unlock_up_safe(struct btrfs_path *path, int level)
>  		path->locks[i] = 0;
>  	}
>  }
> +
> +int btrfs_drw_lock_init(struct btrfs_drw_lock *lock)
> +{
> +	int ret;
> +
> +	ret = percpu_counter_init(&lock->writers, 0, GFP_KERNEL);
> +	if (ret)
> +		return ret;
> +
> +	atomic_set(&lock->readers, 0);
> +	init_waitqueue_head(&lock->pending_readers);
> +	init_waitqueue_head(&lock->pending_writers);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(btrfs_drw_lock_init);


I have the functions EXPORT_SYMBOL since I have an internal patch which
is hooking this code to locktorture. SO they can be removed.