[dm-devel] [PATCH 1/2] dm-snapshot: introduce account_start_copy and account_end_copy

[Nikos Tsironis]

On 10/2/19 1:14 PM, Mikulas Patocka wrote:
> This is simple refactoring that moves code for modifying the semaphore
> cow_count into separate functions. It is needed by the following patch.
> 
> Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
> Cc: stable at vger.kernel.org	# v5.0+
> Fixes: 721b1d98fb51 ("dm snapshot: Fix excessive memory usage and workqueue stalls")
> 

Reviewed-by: Nikos Tsironis <ntsironis at arrikto.com>

> ---
>  drivers/md/dm-snap.c |   20 +++++++++++++++-----
>  1 file changed, 15 insertions(+), 5 deletions(-)
> 
> Index: linux-2.6/drivers/md/dm-snap.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-snap.c	2019-10-01 15:19:20.000000000 +0200
> +++ linux-2.6/drivers/md/dm-snap.c	2019-10-01 15:23:10.000000000 +0200
> @@ -1512,6 +1512,16 @@ static void snapshot_dtr(struct dm_targe
>  	kfree(s);
>  }
>  
> +static void account_start_copy(struct dm_snapshot *s)
> +{
> +	down(&s->cow_count);
> +}
> +
> +static void account_end_copy(struct dm_snapshot *s)
> +{
> +	up(&s->cow_count);
> +}
> +
>  /*
>   * Flush a list of buffers.
>   */
> @@ -1732,7 +1742,7 @@ static void copy_callback(int read_err,
>  		rb_link_node(&pe->out_of_order_node, parent, p);
>  		rb_insert_color(&pe->out_of_order_node, &s->out_of_order_tree);
>  	}
> -	up(&s->cow_count);
> +	account_end_copy(s);
>  }
>  
>  /*
> @@ -1756,7 +1766,7 @@ static void start_copy(struct dm_snap_pe
>  	dest.count = src.count;
>  
>  	/* Hand over to kcopyd */
> -	down(&s->cow_count);
> +	account_start_copy(s);
>  	dm_kcopyd_copy(s->kcopyd_client, &src, 1, &dest, 0, copy_callback, pe);
>  }
>  
> @@ -1776,7 +1786,7 @@ static void start_full_bio(struct dm_sna
>  	pe->full_bio = bio;
>  	pe->full_bio_end_io = bio->bi_end_io;
>  
> -	down(&s->cow_count);
> +	account_start_copy(s);
>  	callback_data = dm_kcopyd_prepare_callback(s->kcopyd_client,
>  						   copy_callback, pe);
>  
> @@ -1866,7 +1876,7 @@ static void zero_callback(int read_err,
>  	struct bio *bio = context;
>  	struct dm_snapshot *s = bio->bi_private;
>  
> -	up(&s->cow_count);
> +	account_end_copy(s);
>  	bio->bi_status = write_err ? BLK_STS_IOERR : 0;
>  	bio_endio(bio);
>  }
> @@ -1880,7 +1890,7 @@ static void zero_exception(struct dm_sna
>  	dest.sector = bio->bi_iter.bi_sector;
>  	dest.count = s->store->chunk_size;
>  
> -	down(&s->cow_count);
> +	account_start_copy(s);
>  	WARN_ON_ONCE(bio->bi_private);
>  	bio->bi_private = s;
>  	dm_kcopyd_zero(s->kcopyd_client, 1, &dest, 0, zero_callback, bio);
>