Re: [PATCH net] octeontx2-af: npc: cn20k: Fix subbank free list indexing for search order

[Simon Horman <horms@kernel.org>]

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---
octeontx2-af: npc: cn20k: Fix subbank free list indexing for search order

This change re-keys the xa_sb_free free list using each subbank's slot
in subbank_srch_order[] rather than using subbank_srch_order[sb->idx],
moving the population into a new helper called from npc_priv_init().
A few comments inline.

> diff --git a/drivers/net/ethernet/marvell/octeontx2/af/cn20k/npc.c b/drivers/net/ethernet/marvell/octeontx2/af/cn20k/npc.c
> index 354c4e881c6a..d38e848add93 100644
> --- a/drivers/net/ethernet/marvell/octeontx2/af/cn20k/npc.c
> +++ b/drivers/net/ethernet/marvell/octeontx2/af/cn20k/npc.c
> @@ -3423,6 +3423,36 @@ static int npc_create_srch_order(int cnt)
>  	return 0;
>  }
>  
> +static int npc_subbanks_srch_oder_init(struct rvu *rvu)
                                ^^^^

[Low]
Is "oder" intended here? The neighbouring identifiers
npc_create_srch_order() and subbank_srch_order use "order", so this
appears to be a typo that would be easier to fix before the symbol
lands.

> +{
> +	struct npc_subbank *sb;
> +	int sb_idx;
> +	int i, j;
> +	int rc;
> +
> +	for (i = 0; i < npc_priv->num_subbanks; i++) {
> +		sb_idx = subbank_srch_order[i];
> +		sb = &npc_priv->sb[sb_idx];
> +		sb->arr_idx = i;
> +
> +		dev_dbg(rvu->dev, "%s: sb->idx=%u sb->arr_idx=%u\n",
> +			__func__, sb->idx, sb->arr_idx);
> +
> +		rc = xa_err(xa_store(&npc_priv->xa_sb_free, sb->arr_idx,
> +				     xa_mk_value(sb->idx), GFP_KERNEL));
> +		if (rc) {
> +			dev_err(rvu->dev,
> +				"%s: xa_store(xa_sb_free) failed at slot %d (sb=%d): %d\n",
> +				__func__, i, sb_idx, rc);
> +			for (j = 0; j < i; j++)
> +				xa_erase(&npc_priv->xa_sb_free, j);
> +			return rc;
> +		}
> +	}
> +
> +	return 0;
> +}
> +

[ ... ]

> @@ -4727,6 +4748,10 @@ static int npc_priv_init(struct rvu *rvu)
>  	for (i = 0, sb = npc_priv->sb; i < num_subbanks; i++, sb++)
>  		npc_subbank_init(rvu, sb, i);
>  
> +	ret = npc_subbanks_srch_oder_init(rvu);
> +	if (ret)
> +		goto fail2;
> +

[Medium]
Can this leak subbank_srch_order on the new failure path?

npc_create_srch_order() allocates subbank_srch_order via kcalloc().
Before this patch, the only way to reach fail2 was when
npc_create_srch_order() itself failed and left subbank_srch_order
NULL, so fail2 not freeing it was safe.

With this new goto fail2, subbank_srch_order has already been
allocated, but the fail2 label only frees npc_priv->sb and npc_priv:

fail2:
	xa_destroy(&npc_priv->xa_sb_used);
	[...]
	kfree(npc_priv->sb);
	npc_priv->sb = NULL;
fail1:
	kfree(npc_priv);
	npc_priv = NULL;
	return ret;

A subsequent re-init would unconditionally reassign
subbank_srch_order = kcalloc(...) in npc_create_srch_order(),
permanently leaking the previous buffer.

Should this path go to a new label that also kfree()s
subbank_srch_order, or should fail2 free it?

>  	/* Get number of pcifuncs in the system */
>  	npc_priv->pf_cnt = npc_pcifunc_map_create(rvu);
>  	npc_priv->xa_pf2idx_map = kcalloc(npc_priv->pf_cnt,

[High]
Can npc_priv_init() return 0 on a real failure here?

After npc_subbanks_srch_oder_init() returns successfully, ret is 0.
If the kcalloc() for npc_priv->xa_pf2idx_map fails right after, the
code does goto fail3 which falls through fail2 and fail1 to
return ret, propagating 0 to the caller:

fail3:
	kfree(subbank_srch_order);
	subbank_srch_order = NULL;

fail2:
	[...]
fail1:
	kfree(npc_priv);
	npc_priv = NULL;
	return ret;

The caller npc_cn20k_init() then sees err == 0 and continues into
npc_setup_mcam_section(), which dereferences npc_priv (now NULL).

Pre-patch the function ended in return -ENOMEM, so the fail3 path
returned -ENOMEM unconditionally. Should ret be reset to -ENOMEM
before goto fail3, or should a separate variable be used for the
new helper's return value?

> @@ -4760,7 +4785,7 @@ static int npc_priv_init(struct rvu *rvu)
>  fail1:
>  	kfree(npc_priv);
>  	npc_priv = NULL;
> -	return -ENOMEM;
> +	return ret;
>  }