Subject: Re: [PATCH net-next 03/10] net: sched: refactor block offloads counter usage

From: Vlad Buslov <[email-masked]>
Date: Fri, 23 Aug 2019 10:39:50 +0000

On Fri 23 Aug 2019 at 01:53, Jakub Kicinski <[email-masked]> wrote:
> On Thu, 22 Aug 2019 15:43:46 +0300, Vlad Buslov wrote:
>> Without rtnl lock protection filters can no longer safely manage block
>> offloads counter themselves. Refactor cls API to protect block offloadcnt
>> with tcf_block->cb_lock that is already used to protect driver callback
>> list and nooffloaddevcnt counter. The counter can be modified by concurrent
>> tasks by new functions that execute block callbacks (which is safe with
>> previous patch that changed its type to atomic_t), however, block
>> bind/unbind code that checks the counter value takes cb_lock in write mode
>> to exclude any concurrent modifications. This approach prevents race
>> conditions between bind/unbind and callback execution code but allows for
>> concurrency for tc rule update path.
>>
>> Move block offload counter, filter in hardware counter and filter flags
>> management from classifiers into cls hardware offloads API. Make functions
>> tcf_block_offload_inc() and tcf_block_offload_dec() to be cls API private.
>> Implement following new cls API to be used instead:
>>
>>   tc_setup_cb_add() - non-destructive filter add. If filter that wasn't
>>   already in hardware is successfully offloaded, increment block offloads
>>   counter, set filter in hardware counter and flag. On failure, previously
>>   offloaded filter is considered to be intact and offloads counter is not
>>   decremented.
>>
>>   tc_setup_cb_replace() - destructive filter replace. Release existing
>>   filter block offload counter and reset its in hardware counter and flag.
>>   Set new filter in hardware counter and flag. On failure, previously
>>   offloaded filter is considered to be destroyed and offload counter is
>>   decremented.
>>
>>   tc_setup_cb_destroy() - filter destroy. Unconditionally decrement block
>>   offloads counter.
>>
>> Refactor all offload-capable classifiers to atomically offload filters to
>> hardware, change block offload counter, and set filter in hardware counter
>> and flag by means of the new cls API functions.
>>
>> Signed-off-by: Vlad Buslov <[email-masked]>
>> Acked-by: Jiri Pirko <[email-masked]>
>
> Looks good, minor nits
>
>> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
>> index 8502bd006b37..4215c849f4a3 100644
>> --- a/net/sched/cls_api.c
>> +++ b/net/sched/cls_api.c
>> @@ -3000,13 +3000,97 @@ int tcf_exts_dump_stats(struct sk_buff *skb, struct tcf_exts *exts)
>>  }
>>  EXPORT_SYMBOL(tcf_exts_dump_stats);
>>
>> -int tc_setup_cb_call(struct tcf_block *block, enum tc_setup_type type,
>> -		     void *type_data, bool err_stop)
>> +static void tcf_block_offload_inc(struct tcf_block *block, u32 *flags)
>> +{
>> +	if (*flags & TCA_CLS_FLAGS_IN_HW)
>> +		return;
>> +	*flags |= TCA_CLS_FLAGS_IN_HW;
>> +	atomic_inc(&block->offloadcnt);
>> +}
>> +
>> +static void tcf_block_offload_dec(struct tcf_block *block, u32 *flags)
>> +{
>> +	if (!(*flags & TCA_CLS_FLAGS_IN_HW))
>> +		return;
>> +	*flags &= ~TCA_CLS_FLAGS_IN_HW;
>> +	atomic_dec(&block->offloadcnt);
>> +}
>> +
>> +void tc_cls_offload_cnt_update(struct tcf_block *block, struct tcf_proto *tp,
>> +			       u32 *cnt, u32 *flags, u32 diff, bool add)
>> +{
>> +	lockdep_assert_held(&block->cb_lock);
>> +
>> +	spin_lock(&tp->lock);
>> +	if (add) {
>> +		if (!*cnt)
>> +			tcf_block_offload_inc(block, flags);
>> +		(*cnt) += diff;
>
> brackets unnecessary
>
>> +	} else {
>> +		(*cnt) -= diff;
>> +		if (!*cnt)
>> +			tcf_block_offload_dec(block, flags);
>> +	}
>> +	spin_unlock(&tp->lock);
>> +}
>> +EXPORT_SYMBOL(tc_cls_offload_cnt_update);
>> +
>> +static void
>> +tc_cls_offload_cnt_reset(struct tcf_block *block, struct tcf_proto *tp,
>> +			 u32 *cnt, u32 *flags)
>> +{
>> +	lockdep_assert_held(&block->cb_lock);
>> +
>> +	spin_lock(&tp->lock);
>> +	tcf_block_offload_dec(block, flags);
>> +	(*cnt) = 0;
>
> ditto
>
>> +	spin_unlock(&tp->lock);
>> +}
>> +
>> +static int
>> +__tc_setup_cb_call(struct tcf_block *block, enum tc_setup_type type,
>> +		   void *type_data, bool err_stop)
>>  {
>>  	struct flow_block_cb *block_cb;
>>  	int ok_count = 0;
>>  	int err;
>>
>> +	list_for_each_entry(block_cb, &block->flow_block.cb_list, list) {
>> +		err = block_cb->cb(type, type_data, block_cb->cb_priv);
>> +		if (err) {
>> +			if (err_stop)
>> +				return err;
>> +		} else {
>> +			ok_count++;
>> +		}
>> +	}
>> +	return ok_count;
>> +}
>> +
>> +int tc_setup_cb_call(struct tcf_block *block, enum tc_setup_type type,
>> +		     void *type_data, bool err_stop, bool rtnl_held)
>> +{
>> +	int ok_count;
>> +
>> +	down_read(&block->cb_lock);
>> +	ok_count = __tc_setup_cb_call(block, type, type_data, err_stop);
>> +	up_read(&block->cb_lock);
>> +	return ok_count;
>> +}
>> +EXPORT_SYMBOL(tc_setup_cb_call);
>> +
>> +/* Non-destructive filter add. If filter that wasn't already in hardware is
>> + * successfully offloaded, increment block offloads counter. On failure,
>> + * previously offloaded filter is considered to be intact and offloads counter
>> + * is not decremented.
>> + */
>> +
>
> Spurious new line here?
>
>> +int tc_setup_cb_add(struct tcf_block *block, struct tcf_proto *tp,
>> +		    enum tc_setup_type type, void *type_data, bool err_stop,
>> +		    u32 *flags, unsigned int *in_hw_count, bool rtnl_held)
>> +{
>> +	int ok_count;
>> +
>>  	down_read(&block->cb_lock);
>>  	/* Make sure all netdevs sharing this block are offload-capable. */
>>  	if (block->nooffloaddevcnt && err_stop) {
>> @@ -3014,22 +3098,67 @@ int tc_setup_cb_call(struct tcf_block *block, enum tc_setup_type type,
>>  		goto errout;
>>  	}
>>
>> -	list_for_each_entry(block_cb, &block->flow_block.cb_list, list) {
>> -		err = block_cb->cb(type, type_data, block_cb->cb_priv);
>> -		if (err) {
>> -			if (err_stop) {
>> -				ok_count = err;
>> -				goto errout;
>> -			}
>> -		} else {
>> -			ok_count++;
>> -		}
>> +	ok_count = __tc_setup_cb_call(block, type, type_data, err_stop);
>> +	if (ok_count > 0)
>> +		tc_cls_offload_cnt_update(block, tp, in_hw_count, flags,
>> +					  ok_count, true);
>> +errout:
>
> and the labels again
>
>> +	up_read(&block->cb_lock);
>> +	return ok_count;
>> +}
>> +EXPORT_SYMBOL(tc_setup_cb_add);
>> +
>> +/* Destructive filter replace. If filter that wasn't already in hardware is
>> + * successfully offloaded, increment block offload counter. On failure,
>> + * previously offloaded filter is considered to be destroyed and offload counter
>> + * is decremented.
>> + */
>> +
>
> spurious new line?
>
>> +int tc_setup_cb_replace(struct tcf_block *block, struct tcf_proto *tp,
>> +			enum tc_setup_type type, void *type_data, bool err_stop,
>> +			u32 *old_flags, unsigned int *old_in_hw_count,
>> +			u32 *new_flags, unsigned int *new_in_hw_count,
>> +			bool rtnl_held)
>> +{
>> +	int ok_count;
>> +
>> +	down_read(&block->cb_lock);
>> +	/* Make sure all netdevs sharing this block are offload-capable. */
>> +	if (block->nooffloaddevcnt && err_stop) {
>> +		ok_count = -EOPNOTSUPP;
>> +		goto errout;
>>  	}
>> +
>> +	tc_cls_offload_cnt_reset(block, tp, old_in_hw_count, old_flags);
>> +
>> +	ok_count = __tc_setup_cb_call(block, type, type_data, err_stop);
>> +	if (ok_count > 0)
>> +		tc_cls_offload_cnt_update(block, tp, new_in_hw_count, new_flags,
>> +					  ok_count, true);
>>  errout:
>>  	up_read(&block->cb_lock);
>>  	return ok_count;
>>  }
>> -EXPORT_SYMBOL(tc_setup_cb_call);
>> +EXPORT_SYMBOL(tc_setup_cb_replace);
>> +
>> +/* Destroy filter and decrement block offload counter, if filter was previously
>> + * offloaded.
>> + */
>> +
>
> hm.. is this gap between comment and function it pertains to
> intentional?

Majority of function comments in cls_api.c have newline after them (not
all of them though). I don't have any strong opinions regarding this.
You suggest it is better not to have blank lines after function
comments?

>
>> +int tc_setup_cb_destroy(struct tcf_block *block, struct tcf_proto *tp,
>> +			enum tc_setup_type type, void *type_data, bool err_stop,
>> +			u32 *flags, unsigned int *in_hw_count, bool rtnl_held)
>> +{
>> +	int ok_count;
>> +
>> +	down_read(&block->cb_lock);
>> +	ok_count = __tc_setup_cb_call(block, type, type_data, err_stop);
>> +
>> +	tc_cls_offload_cnt_reset(block, tp, in_hw_count, flags);
>> +	up_read(&block->cb_lock);
>> +	return ok_count;
>> +}
>> +EXPORT_SYMBOL(tc_setup_cb_destroy);
>>
>>  int tc_setup_flow_action(struct flow_action *flow_action,
>>  			 const struct tcf_exts *exts)
>> diff --git a/net/sched/cls_bpf.c b/net/sched/cls_bpf.c
>> index 3f7a9c02b70c..7f304db7e697 100644
>> --- a/net/sched/cls_bpf.c
>> +++ b/net/sched/cls_bpf.c
>> @@ -162,17 +162,21 @@ static int cls_bpf_offload_cmd(struct tcf_proto *tp, struct cls_bpf_prog *prog,
>>  	cls_bpf.name = obj->bpf_name;
>>  	cls_bpf.exts_integrated = obj->exts_integrated;
>>
>> -	if (oldprog)
>> -		tcf_block_offload_dec(block, &oldprog->gen_flags);
>> +	if (cls_bpf.oldprog)
>
> why the change from oldprog to cls_bpf.oldprog?

No reason. Looks like a mistake I made when rewriting the conditional
for new tc_setup_cb_*() API.

>
>> +		err = tc_setup_cb_replace(block, tp, TC_SETUP_CLSBPF, &cls_bpf,
>> +					  skip_sw, &oldprog->gen_flags,
>> +					  &oldprog->in_hw_count,
>> +					  &prog->gen_flags, &prog->in_hw_count,
>> +					  true);
>> +	else
>> +		err = tc_setup_cb_add(block, tp, TC_SETUP_CLSBPF, &cls_bpf,
>> +				      skip_sw, &prog->gen_flags,
>> +				      &prog->in_hw_count, true);
>>
>> -	err = tc_setup_cb_call(block, TC_SETUP_CLSBPF, &cls_bpf, skip_sw);
>>  	if (prog) {
>>  		if (err < 0) {
>>  			cls_bpf_offload_cmd(tp, oldprog, prog, extack);
>>  			return err;
>> -		} else if (err > 0) {
>> -			prog->in_hw_count = err;
>> -			tcf_block_offload_inc(block, &prog->gen_flags);
>>  		}
>>  	}
>>
>> @@ -230,7 +234,7 @@ static void cls_bpf_offload_update_stats(struct tcf_proto *tp,
>>  	cls_bpf.name = prog->bpf_name;
>>  	cls_bpf.exts_integrated = prog->exts_integrated;
>>
>> -	tc_setup_cb_call(block, TC_SETUP_CLSBPF, &cls_bpf, false);
>> +	tc_setup_cb_call(block, TC_SETUP_CLSBPF, &cls_bpf, false, true);
>>  }
>>
>>  static int cls_bpf_init(struct tcf_proto *tp)
>> @@ -680,8 +684,8 @@ static int cls_bpf_reoffload(struct tcf_proto *tp, bool add, flow_setup_cb_t *cb
>>  			continue;
>>  		}
>>
>> -		tc_cls_offload_cnt_update(block, &prog->in_hw_count,
>> -					  &prog->gen_flags, add);
>> +		tc_cls_offload_cnt_update(block, tp, &prog->in_hw_count,
>> +					  &prog->gen_flags, 1, add);
>
> Since we're adding those higher level add/replace/destroy helpers,
> would it also be possible to have a helper which takes care of
> reoffload? tc_cls_offload_cnt_update() is kind of low level now, it'd
> be cool to also hide it in the core.

Agree. I'll try to come up with something more elegant.

>
>>  	}
>>
>>  	return 0;
>> diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
>> index 054123742e32..0001a933d48b 100644
>> --- a/net/sched/cls_flower.c
>> +++ b/net/sched/cls_flower.c
>> @@ -419,10 +419,10 @@ static void fl_hw_destroy_filter(struct tcf_proto *tp, struct cls_fl_filter *f,
>>  	cls_flower.command = FLOW_CLS_DESTROY;
>>  	cls_flower.cookie = (unsigned long) f;
>>
>> -	tc_setup_cb_call(block, TC_SETUP_CLSFLOWER, &cls_flower, false);
>> +	tc_setup_cb_destroy(block, tp, TC_SETUP_CLSFLOWER, &cls_flower, false,
>> +			    &f->flags, &f->in_hw_count, true);
>>  	spin_lock(&tp->lock);
>>  	list_del_init(&f->hw_list);
>> -	tcf_block_offload_dec(block, &f->flags);
>>  	spin_unlock(&tp->lock);
>>
>>  	if (!rtnl_held)
>> @@ -466,18 +466,15 @@ static int fl_hw_replace_filter(struct tcf_proto *tp,
>>  		goto errout;
>>  	}
>>
>> -	err = tc_setup_cb_call(block, TC_SETUP_CLSFLOWER, &cls_flower, skip_sw);
>> +	err = tc_setup_cb_add(block, tp, TC_SETUP_CLSFLOWER, &cls_flower,
>> +			      skip_sw, &f->flags, &f->in_hw_count, true);
>>  	kfree(cls_flower.rule);
>>
>>  	if (err < 0) {
>>  		fl_hw_destroy_filter(tp, f, true, NULL);
>>  		goto errout;
>>  	} else if (err > 0) {
>> -		f->in_hw_count = err;
>>  		err = 0;
>
> Why does the tc_setup_cb* API still return the positive values, the
> callers should no longer care, right?

Yep. I'll refactor this for V2 and simplify related conditionals in
classifiers.

>
>> -		spin_lock(&tp->lock);
>> -		tcf_block_offload_inc(block, &f->flags);
>> -		spin_unlock(&tp->lock);
>>  	}
>>
>>  	if (skip_sw && !(f->flags & TCA_CLS_FLAGS_IN_HW)) {