Re: [dpdk-dev] [PATCH v2] lpm: fix unchecked return value

[Bruce Richardson <bruce.richardson@intel.com>]

On Tue, Jul 21, 2020 at 05:23:02PM +0100, Medvedkin, Vladimir wrote:
> Hi Ruifeng,
> 
> On 18/07/2020 10:22, Ruifeng Wang wrote:
> > 
> > > -----Original Message-----
> > > From: Medvedkin, Vladimir <vladimir.medvedkin@intel.com>
> > > Sent: Saturday, July 18, 2020 1:12 AM
> > > To: Ruifeng Wang <Ruifeng.Wang@arm.com>; Bruce Richardson
> > > <bruce.richardson@intel.com>
> > > Cc: dev@dpdk.org; nd <nd@arm.com>; Honnappa Nagarahalli
> > > <Honnappa.Nagarahalli@arm.com>; Phil Yang <Phil.Yang@arm.com>
> > > Subject: Re: [PATCH v2] lpm: fix unchecked return value
> > > 
> > > Hi Ruifeng,
> > > 
> > Hi Vladimir,
> > 
> > > On 16/07/2020 16:49, Ruifeng Wang wrote:
> > > > Coverity complains about unchecked return value of
> > > rte_rcu_qsbr_dq_enqueue.
> > > > By default, defer queue size is big enough to hold all tbl8 groups.
> > > > When enqueue fails, return error to the user to indicate system issue.
> > > > 
> > > > Coverity issue: 360832
> > > > Fixes: 8a9f8564e9f9 ("lpm: implement RCU rule reclamation")
> > > > 
> > > > Signed-off-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > > > ---
> > > > v2:
> > > > Converted return value to conform to LPM API convention. (Vladimir)
> > > > 
> > > >    lib/librte_lpm/rte_lpm.c | 19 +++++++++++++------
> > > >    1 file changed, 13 insertions(+), 6 deletions(-)
> > > > 
> > > > diff --git a/lib/librte_lpm/rte_lpm.c b/lib/librte_lpm/rte_lpm.c index
> > > > 2db9e16a2..757436f49 100644
> > > > --- a/lib/librte_lpm/rte_lpm.c
> > > > +++ b/lib/librte_lpm/rte_lpm.c
> > > > @@ -532,11 +532,12 @@ tbl8_alloc(struct rte_lpm *lpm)
> > > >    	return group_idx;
> > > >    }
> > > > 
> > > > -static void
> > > > +static int32_t
> > > >    tbl8_free(struct rte_lpm *lpm, uint32_t tbl8_group_start)
> > > >    {
> > > >    	struct rte_lpm_tbl_entry zero_tbl8_entry = {0};
> > > >    	struct __rte_lpm *internal_lpm;
> > > > +	int status;
> > > > 
> > > >    	internal_lpm = container_of(lpm, struct __rte_lpm, lpm);
> > > >    	if (internal_lpm->v == NULL) {
> > > > @@ -552,9 +553,15 @@ tbl8_free(struct rte_lpm *lpm, uint32_t
> > > tbl8_group_start)
> > > >    				__ATOMIC_RELAXED);
> > > >    	} else if (internal_lpm->rcu_mode == RTE_LPM_QSBR_MODE_DQ) {
> > > >    		/* Push into QSBR defer queue. */
> > > > -		rte_rcu_qsbr_dq_enqueue(internal_lpm->dq,
> > > > +		status = rte_rcu_qsbr_dq_enqueue(internal_lpm->dq,
> > > >    				(void *)&tbl8_group_start);
> > > > +		if (status == 1) {
> > > > +			RTE_LOG(ERR, LPM, "Failed to push QSBR FIFO\n");
> > > > +			return -rte_errno;
> > > > +		}
> > > >    	}
> > > > +
> > > > +	return 0;
> > > >    }
> > > > 
> > > >    static __rte_noinline int32_t
> > > > @@ -1040,7 +1047,7 @@ delete_depth_big(struct rte_lpm *lpm, uint32_t
> > > ip_masked,
> > > >    #define group_idx next_hop
> > > >    	uint32_t tbl24_index, tbl8_group_index, tbl8_group_start,
> > > tbl8_index,
> > > >    			tbl8_range, i;
> > > > -	int32_t tbl8_recycle_index;
> > > > +	int32_t tbl8_recycle_index, status = 0;
> > > > 
> > > >    	/*
> > > >    	 * Calculate the index into tbl24 and range. Note: All depths
> > > > larger @@ -1097,7 +1104,7 @@ delete_depth_big(struct rte_lpm *lpm,
> > > uint32_t ip_masked,
> > > >    		 */
> > > >    		lpm->tbl24[tbl24_index].valid = 0;
> > > >    		__atomic_thread_fence(__ATOMIC_RELEASE);
> > > > -		tbl8_free(lpm, tbl8_group_start);
> > > > +		status = tbl8_free(lpm, tbl8_group_start);
> > > >    	} else if (tbl8_recycle_index > -1) {
> > > >    		/* Update tbl24 entry. */
> > > >    		struct rte_lpm_tbl_entry new_tbl24_entry = { @@ -1113,10
> > > +1120,10
> > > > @@ delete_depth_big(struct rte_lpm *lpm, uint32_t ip_masked,
> > > >    		__atomic_store(&lpm->tbl24[tbl24_index],
> > > &new_tbl24_entry,
> > > >    				__ATOMIC_RELAXED);
> > > >    		__atomic_thread_fence(__ATOMIC_RELEASE);
> > > > -		tbl8_free(lpm, tbl8_group_start);
> > > > +		status = tbl8_free(lpm, tbl8_group_start);
> > > >    	}
> > > >    #undef group_idx
> > > > -	return 0;
> > > > +	return status;
> > > 
> > > This will change rte_lpm_delete API. As a suggestion, you can leave it as it
> > > was before ("return 0"), and send separate patch (with "return status)"
> > > which will be targeted to 20.11.
> > > 
> > 
> > Is the change of API  because a variable is returned instead of constant?
> > The patch passed ABI check on Travis: http://mails.dpdk.org/archives/test-report/2020-July/144864.html
> > So I didn't know there is API/ABI issue.
> 
> 
> Because new error status codes are returned. At the moment rte_lpm_delete()
> returns only -EINVAL. After patches it will also returns -ENOSPC. The user's
> code may not handle this returned error status.
> 
> On the other hand, from documentation about returned value:
> "0 on success, negative value otherwise",
> and given the fact that this behavior is only after calling
> rte_lpm_rcu_qsbr_add(), I think we can accept this patch.
> Bruce, please correct me.
> 
That sounds reasonable to me. No change in the committed ABI, since the
specific values are not called out.