Re: [Devel] [PATCH VZ10 v2 01/10] drivers/md/dm-qcow2: fix revert_cluster_alloc() for ext_l2 case

[Pavel Tikhomirov <ptikhomirov@virtuozzo.com>]

On 8/12/26 22:19, Andrey Zhadchenko wrote:
> This function walks over all changed u64 values in md. With ext_l2
> half of them holds subcluster description. Firstly it reverts these
> values to saved pe_page, which is fine, but then it tries to revert
> r1r2 changes. It makes no sense when the value is a subcluster
> description.
> Teach the function to skip subcluster descriptions: do it based on
> a new lx_level in struct wb_desc. Add new argument to
> prepare_l_entry_update() and set it there.
> The warning also could have tripped for ext_l2 entries, so drop
> it entirely.
> The function effectively reverts not only cluster alloc, so rename
> it to revert_l_entries_update() to mimic prepare_l_entries_update.

prepare_l_entrie(s)_update is probably a misspelled prepare_l_entry_update

> 
> Feature: dm-qcow2: block device over QCOW2 files driver
> https://virtuozzo.atlassian.net/browse/VSTOR-139406
> Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko@virtuozzo.com>
> ---
>  drivers/md/dm-qcow2-map.c    | 28 ++++++++++++++++++----------
>  drivers/md/dm-qcow2-target.c |  2 +-
>  drivers/md/dm-qcow2.h        |  1 +
>  3 files changed, 20 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/md/dm-qcow2-map.c b/drivers/md/dm-qcow2-map.c
> index db21efb45e17a..2cd8e174049f8 100644
> --- a/drivers/md/dm-qcow2-map.c
> +++ b/drivers/md/dm-qcow2-map.c
> @@ -1297,18 +1297,19 @@ static void do_md_page_read_complete(int ret, struct qcow2 *qcow2,
>  }
>  
>  /* Be careful with dirty_or_writeback()/etc! Check races. */
> -static void revert_clusters_alloc(struct qcow2 *qcow2, struct wb_desc *wbd)
> +static void revert_l_entries_update(struct qcow2 *qcow2, struct wb_desc *wbd)
>  {
>  	struct qcow2_map_item r1, r2;
>  	struct page *pe_page;
> +	bool skip_odd;
>  	u64 pos, old;
>  	int i, ret;
>  
> +	skip_odd = qcow2->ext_l2 && wbd->lx_level == L2_LEVEL;
> +
>  	lockdep_assert_held(&qcow2->md_pages_lock);
>  	for_each_set_bit(i, wbd->changed_indexes, LX_INDEXES_PER_PAGE) {
>  		pos = get_u64_from_be_page(wbd->md->page, i);
> -		WARN_ON_ONCE(!(pos & ~LX_REFCOUNT_EXACTLY_ONE) ||
> -			     !(pos & LX_REFCOUNT_EXACTLY_ONE));
>  
>  		/* Here we restore prealloced and compressed clu mappings */
>  		pe_page = wbd->pe_page;
> @@ -1321,6 +1322,9 @@ static void revert_clusters_alloc(struct qcow2 *qcow2, struct wb_desc *wbd)
>  		}
>  
>  		set_u64_to_be_page(wbd->md->page, i, 0);
> +		if (skip_odd && (i & 1))
> +			continue; /* pos contains ext_l2 part of L2 entry */
> +
>  		spin_unlock(&qcow2->md_pages_lock);
>  		pos &= ~LX_REFCOUNT_EXACTLY_ONE;
>  
> @@ -1369,7 +1373,7 @@ static void complete_wbd(struct qcow2 *qcow2, struct wb_desc *wbd)
>  		unsigned long flags;
>  
>  		spin_lock_irqsave(&qcow2->md_pages_lock, flags);
> -		revert_clusters_alloc(qcow2, wbd);
> +		revert_l_entries_update(qcow2, wbd);
>  		clear_writeback_status(qcow2, wbd->md, wbd->ret,
>  				       &wait_list, &end_list);
>  		spin_unlock_irqrestore(&qcow2->md_pages_lock, flags);
> @@ -2433,7 +2437,7 @@ static loff_t allocate_cluster(struct qcow2 *qcow2, struct qio *qio,
>  #define LU_IGN_CHANGED_IND	(1 << 3)
>  static int prepare_l_entry_update(struct qcow2 *qcow2, struct qio *qio,
>  				  struct md_page *md, u32 index_in_page,
> -				  u64 *pval, u32 arg_mask)
> +				  u64 *pval, u32 arg_mask, u8 lx_level)
>  {
>  	bool wants_pe_page = (arg_mask & LU_WANTS_PE_PAGE);
>  	struct wb_desc *new_wbd = NULL;
> @@ -2453,6 +2457,7 @@ static int prepare_l_entry_update(struct qcow2 *qcow2, struct qio *qio,
>  		if (!new_wbd)
>  			return -ENOMEM;
>  		new_wbd->md = md;
> +		new_wbd->lx_level = lx_level;
>  	} else if (wants_pe_page && !md->wbd->pe_page) {
>  		pe_page = alloc_page(GFP_NOIO|__GFP_ZERO);
>  		if (!pe_page)
> @@ -2515,7 +2520,8 @@ static int prepare_l1l2_allocation(struct qcow2 *qcow2, struct qio *qio,
>  		/* Allocate cluster for L2 entries, and prepare L1 update */
>  		ret = prepare_l_entry_update(qcow2, qio, map->l1.md,
>  					     map->l1.index_in_page, &val,
> -					     LU_SET_ONE_MASK|LU_WANTS_ALLOC);
> +					     LU_SET_ONE_MASK|LU_WANTS_ALLOC,
> +					     L1_LEVEL);
>  		if (ret <= 0)
>  			return ret;
>  
> @@ -2541,7 +2547,8 @@ static int prepare_l1l2_allocation(struct qcow2 *qcow2, struct qio *qio,
>  
>  		ret = prepare_l_entry_update(qcow2, qio, map->l2.md,
>  					     map->l2.index_in_page,
> -					     &map->data_clu_pos, arg_mask);
> +					     &map->data_clu_pos, arg_mask,
> +					     L2_LEVEL);
>  		if (ret <= 0)
>  			return ret;
>  
> @@ -2562,7 +2569,7 @@ static int prepare_l1l2_allocation(struct qcow2 *qcow2, struct qio *qio,
>  
>  	return prepare_l_entry_update(qcow2, qio, map->l2.md,
>  				      map->l2.index_in_page + 1,
> -				      &val, arg_mask);
> +				      &val, arg_mask, L2_LEVEL);
>  }
>  
>  /*
> @@ -3975,7 +3982,7 @@ static void process_cow_indexes_write(struct qcow2 *qcow2,
>  		ret = prepare_l_entry_update(qcow2, qio, lx_md,
>  					     ext->lx_index_in_page,
>  					     &ext->allocated_clu_pos,
> -					     arg_mask);
> +					     arg_mask, ext->cow_level);
>  		if (ret < 0) {
>  			qio->bi_status = errno_to_blk_status(ret);
>  			qio_endio(qio);
> @@ -3986,7 +3993,8 @@ static void process_cow_indexes_write(struct qcow2 *qcow2,
>  			arg_mask &= ~LU_SET_ONE_MASK;
>  			ret = prepare_l_entry_update(qcow2, qio, lx_md,
>  					     ext->lx_index_in_page + 1,
> -					   &ext->new_ext_l2, arg_mask);
> +					     &ext->new_ext_l2, arg_mask,
> +					     L2_LEVEL);
>  			WARN_ON_ONCE(ret < 0);
>  		}
>  
> diff --git a/drivers/md/dm-qcow2-target.c b/drivers/md/dm-qcow2-target.c
> index 3f65897ce9da2..0f1d3e3c5258e 100644
> --- a/drivers/md/dm-qcow2-target.c
> +++ b/drivers/md/dm-qcow2-target.c
> @@ -174,7 +174,7 @@ void qcow2_flush_deferred_activity(struct qcow2_target *tgt, struct qcow2 *qcow2
>  	int i;
>  
>  	/*
> -	 * We need second iteration, since revert_clusters_alloc()
> +	 * We need second iteration, since revert_l_entries_update()
>  	 * may start timer again after failed wb.
>  	 */
>  	for (i = 0; i < 2; i++) {
> diff --git a/drivers/md/dm-qcow2.h b/drivers/md/dm-qcow2.h
> index 86f0688e7345a..aa3487007523f 100644
> --- a/drivers/md/dm-qcow2.h
> +++ b/drivers/md/dm-qcow2.h
> @@ -118,6 +118,7 @@ struct wb_desc {
>  	struct list_head dependent_list;
>  	int nr_submitted;
>  	bool completed;
> +	u8 lx_level;
>  	int ret;
>  };
>  

-- 
Best regards, Pavel Tikhomirov
Senior Software Developer, Virtuozzo.