Re: [PATCH] ocfs2: fixing global bitmap allocating failure for discontig type

[Joseph Qi]

On 2025/3/27 14:22, Heming Zhao wrote:
> The commit 4eb7b93e0310 ("ocfs2: improve write IO performance when
> fragmentation is high") introduced a regression. In the discontiguous
> extent allocation case, ocfs2_cluster_group_search() is comparing with
> the wrong target length, which causes allocation failure.
> 
> Call stack:
> ocfs2_mkdir()
>  ocfs2_reserve_new_inode()
>   ocfs2_reserve_suballoc_bits()
>    ocfs2_block_group_alloc()
>     ocfs2_block_group_alloc_discontig()
>      __ocfs2_claim_clusters()
>       ocfs2_claim_suballoc_bits()
>        ocfs2_search_chain()
>         ocfs2_cluster_group_search()
> 
> Reported-by: Gautham Ananthakrishna <gautham.ananthakrishna@xxxxxxxxxx>
> Fixes: 4eb7b93e0310 ("ocfs2: improve write IO performance when fragmentation is high")
> Signed-off-by: Heming Zhao <heming.zhao@xxxxxxxx>
> ---
>  fs/ocfs2/suballoc.c | 14 +++++++++++---
>  fs/ocfs2/suballoc.h |  1 +
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
> index f7b483f0de2a..3dea082f6e91 100644
> --- a/fs/ocfs2/suballoc.c
> +++ b/fs/ocfs2/suballoc.c
> @@ -698,10 +698,12 @@ static int ocfs2_block_group_alloc(struct ocfs2_super *osb,
>  
>  	bg_bh = ocfs2_block_group_alloc_contig(osb, handle, alloc_inode,
>  					       ac, cl);
> -	if (PTR_ERR(bg_bh) == -ENOSPC)
> +	if (PTR_ERR(bg_bh) == -ENOSPC) {
> +		ac->ac_which = OCFS2_AC_USE_MAIN_DISCONTIG;
>  		bg_bh = ocfs2_block_group_alloc_discontig(handle,
>  							  alloc_inode,
>  							  ac, cl);
> +	}
>  	if (IS_ERR(bg_bh)) {
>  		status = PTR_ERR(bg_bh);
>  		bg_bh = NULL;
> @@ -2365,7 +2367,8 @@ int __ocfs2_claim_clusters(handle_t *handle,
>  	BUG_ON(ac->ac_bits_given >= ac->ac_bits_wanted);
>  
>  	BUG_ON(ac->ac_which != OCFS2_AC_USE_LOCAL
> -	       && ac->ac_which != OCFS2_AC_USE_MAIN);
> +	       && ac->ac_which != OCFS2_AC_USE_MAIN
> +	       && ac->ac_which != OCFS2_AC_USE_MAIN_DISCONTIG);
>  
>  	if (ac->ac_which == OCFS2_AC_USE_LOCAL) {
>  		WARN_ON(min_clusters > 1);
> @@ -2427,7 +2430,12 @@ int ocfs2_claim_clusters(handle_t *handle,
>  			 u32 *cluster_start,
>  			 u32 *num_clusters)
>  {
> -	unsigned int bits_wanted = ac->ac_bits_wanted - ac->ac_bits_given;
> +	unsigned int bits_wanted;
> +
> +	if (ac->ac_which == OCFS2_AC_USE_MAIN)
> +		bits_wanted = ac->ac_bits_wanted - ac->ac_bits_given;
> +	else /* ac_which == OCFS2_AC_USE_MAIN_DISCONTIG */
> +		bits_wanted = min_clusters;

This looks wried. Why can not be other alloc type?

Or it seems you intend to:

unsigned int bits_wanted = ac->ac_bits_wanted - ac->ac_bits_given;

if (ac->ac_which == OCFS2_AC_USE_MAIN_DISCONTIG)
	bits_wanted = min_clusters;

Thanks,
Joseph

>  
>  	return __ocfs2_claim_clusters(handle, ac, min_clusters,
>  				      bits_wanted, cluster_start, num_clusters);
> diff --git a/fs/ocfs2/suballoc.h b/fs/ocfs2/suballoc.h
> index b481b834857d..bcf2ed4a8631 100644
> --- a/fs/ocfs2/suballoc.h
> +++ b/fs/ocfs2/suballoc.h
> @@ -29,6 +29,7 @@ struct ocfs2_alloc_context {
>  #define OCFS2_AC_USE_MAIN  2
>  #define OCFS2_AC_USE_INODE 3
>  #define OCFS2_AC_USE_META  4
> +#define OCFS2_AC_USE_MAIN_DISCONTIG  5
>  	u32    ac_which;
>  
>  	/* these are used by the chain search */