[Ocfs2-devel] [PATCH] ocfs2: Fix wrong search logic in __ocfs2_resv_find_window

[Joseph Qi]

Hi,
Could you please share a reproducer?

Thanks,
Joseph

On 4/6/23 11:40 PM, Heming Zhao wrote:
> ** problem **
> 
> Current code triggers a defragfs bug [1]:
> 
> ```
> tw-tst:~ # defragfs.ocfs2 /mnt/test_from_dd1
> defragfs.ocfs2 1.8.7
> [ERROR]Move extent failed:"/mnt/test_from_dd1" - No space left on device
> [ERROR]"/mnt/test_from_dd1":No space left on device
> ```
> 
> I added some debug messages in relevant functions. When above error
> messages appeared, the la-window still had enough continuous bitmap
> to use, the -ENOSPC is wrong.
> 
> ** analysis **
> 
> __ocfs2_resv_find_window should use resv node from rb-tree to do linear
> search. But current code logic uses un-managered area between two resvs.
> The searching logic deviates from this func job, which should only focus
> on reservation areas (when rb_root is non NULL). Another issue of
> __ocfs2_resv_find_window is more inclined to generate inner fragment.
> It doesn't search & consume existing reservations but be apt to create
> new reservation item.
> 
> This patch pulls this func (__ocfs2_resv_find_window) to do what it
> should do: search & consume resev. if this func fails to get suitable
> bitmap area, caller ocfs2_resv_find_window fallbacks to use oldest
> resv from LRU to do the final search.
> 
> [1]: https://bugzilla.suse.com/show_bug.cgi?id=1131931
> 
> Signed-off-by: Heming Zhao <heming.zhao at suse.com>
> ---
>  fs/ocfs2/reservations.c | 48 +++++++++++++++++++++++++++++------------
>  1 file changed, 34 insertions(+), 14 deletions(-)
> 
> diff --git a/fs/ocfs2/reservations.c b/fs/ocfs2/reservations.c
> index a9d1296d736d..eda672622d1d 100644
> --- a/fs/ocfs2/reservations.c
> +++ b/fs/ocfs2/reservations.c
> @@ -458,10 +458,11 @@ static void __ocfs2_resv_find_window(struct ocfs2_reservation_map *resmap,
>  {
>  	struct rb_root *root = &resmap->m_reservations;
>  	unsigned int gap_start, gap_end, gap_len;
> -	struct ocfs2_alloc_reservation *prev_resv, *next_resv;
> +	struct ocfs2_alloc_reservation *prev_resv, *next_resv, *best_resv;
>  	struct rb_node *prev, *next;
>  	unsigned int cstart, clen;
>  	unsigned int best_start = 0, best_len = 0;
> +	int create_new = 0;
>  
>  	/*
>  	 * Nasty cases to consider:
> @@ -540,8 +541,9 @@ static void __ocfs2_resv_find_window(struct ocfs2_reservation_map *resmap,
>  		if (clen) {
>  			best_len = clen;
>  			best_start = cstart;
> +			create_new = 1;
>  			if (best_len == wanted)
> -				goto out_insert;
> +				goto out_create;
>  		}
>  
>  		prev_resv = next_resv;
> @@ -557,13 +559,9 @@ static void __ocfs2_resv_find_window(struct ocfs2_reservation_map *resmap,
>  	while (1) {
>  		next = rb_next(prev);
>  		if (next) {
> -			next_resv = rb_entry(next,
> -					     struct ocfs2_alloc_reservation,
> -					     r_node);
> -
> -			gap_start = ocfs2_resv_end(prev_resv) + 1;
> -			gap_end = next_resv->r_start - 1;
> -			gap_len = gap_end - gap_start + 1;
> +			gap_start = prev_resv->r_start;
> +			gap_end = prev_resv->r_start + prev_resv->r_len - 1;
> +			gap_len = prev_resv->r_len;
>  		} else {
>  			/*
>  			 * We're at the rightmost edge of the
> @@ -575,8 +573,8 @@ static void __ocfs2_resv_find_window(struct ocfs2_reservation_map *resmap,
>  			gap_end = resmap->m_bitmap_len - 1;
>  		}
>  
> -		trace_ocfs2_resv_find_window_next(next ? next_resv->r_start: -1,
> -					next ? ocfs2_resv_end(next_resv) : -1);
> +		trace_ocfs2_resv_find_window_next(next ? prev_resv->r_start : -1,
> +					next ? ocfs2_resv_end(prev_resv) : -1);
>  		/*
>  		 * No need to check this gap if we have already found
>  		 * a larger region of free bits.
> @@ -589,10 +587,16 @@ static void __ocfs2_resv_find_window(struct ocfs2_reservation_map *resmap,
>  		if (clen == wanted) {
>  			best_len = clen;
>  			best_start = cstart;
> -			goto out_insert;
> +			best_resv = prev_resv;
> +			if (!next)
> +				goto out_create;
> +			else
> +				goto out_insert;
>  		} else if (clen > best_len) {
>  			best_len = clen;
>  			best_start = cstart;
> +			best_resv = prev_resv;
> +			create_new = 0;
>  		}
>  
>  next_resv:
> @@ -604,12 +608,28 @@ static void __ocfs2_resv_find_window(struct ocfs2_reservation_map *resmap,
>  				     r_node);
>  	}
>  
> -out_insert:
> -	if (best_len) {
> +	if (!best_len)
> +		return;
> +
> +	if (create_new) {
> +out_create:
>  		resv->r_start = best_start;
>  		resv->r_len = best_len;
>  		ocfs2_resv_insert(resmap, resv);
> +		return;
>  	}
> +
> +out_insert:
> +	if (best_resv->r_len <= wanted) {
> +		resv->r_start = best_start;
> +		resv->r_len = best_len;
> +		__ocfs2_resv_discard(resmap, best_resv);
> +	} else {
> +		best_resv->r_len -= best_len;
> +		resv->r_start = ocfs2_resv_end(best_resv) + 1;
> +		resv->r_len = best_len;
> +	}
> +	ocfs2_resv_insert(resmap, resv);
>  }
>  
>  static void ocfs2_cannibalize_resv(struct ocfs2_reservation_map *resmap,