Commit 67dc6c56 authored by Eric Dumazet's avatar Eric Dumazet Committed by Jakub Kicinski
Browse files

net/sched: sch_cake: annotate data-races in cake_dump_class_stats (II) 



cake_dump_class_stats() runs without qdisc spinlock being held.

In this second patch, I add READ_ONCE()/WRITE_ONCE() annotations for:

- flow->deficit
- flow->cvars.dropping
- flow->cvars.count
- flow->cvars.p_drop
- flow->cvars.blue_timer
- flow->cvars.drop_next

Fixes: 046f6fd5 ("sched: Add Common Applications Kept Enhanced (cake) qdisc")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Acked-by: default avatarToke Høiland-Jørgensen <toke@toke.dk>
Reviewed-by: default avatarSimon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20260430061610.3503483-3-edumazet@google.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 046111a1

net/sched/sch_cake.c

+71 −60
Original line number Diff line number Diff line
@@ -399,14 +399,14 @@ static void cake_configure_rates(struct Qdisc *sch, u64 rate, bool rate_adjust); 
 * Here, invsqrt is a fixed point number (< 1.0), 32bit mantissa, aka Q0.32

 */



static void cobalt_newton_step(struct cobalt_vars *vars)

static void cobalt_newton_step(struct cobalt_vars *vars, u32 count)

{

	u32 invsqrt, invsqrt2;

	u64 val;



	invsqrt = vars->rec_inv_sqrt;

	invsqrt2 = ((u64)invsqrt * invsqrt) >> 32;

	val = (3LL << 32) - ((u64)vars->count * invsqrt2);

	val = (3LL << 32) - ((u64)count * invsqrt2);



	val >>= 2; /* avoid overflow in following multiply */

	val = (val * invsqrt) >> (32 - 2 + 1);
@@ -414,12 +414,12 @@ static void cobalt_newton_step(struct cobalt_vars *vars) 
	vars->rec_inv_sqrt = val;

}



static void cobalt_invsqrt(struct cobalt_vars *vars)

static void cobalt_invsqrt(struct cobalt_vars *vars, u32 count)

{

	if (vars->count < REC_INV_SQRT_CACHE)

		vars->rec_inv_sqrt = inv_sqrt_cache[vars->count];

	if (count < REC_INV_SQRT_CACHE)

		vars->rec_inv_sqrt = inv_sqrt_cache[count];

	else

		cobalt_newton_step(vars);

		cobalt_newton_step(vars, count);

}



static void cobalt_vars_init(struct cobalt_vars *vars)
@@ -449,16 +449,19 @@ static bool cobalt_queue_full(struct cobalt_vars *vars, 
	bool up = false;



	if (ktime_to_ns(ktime_sub(now, vars->blue_timer)) > p->target) {

		up = !vars->p_drop;

		vars->p_drop += p->p_inc;

		if (vars->p_drop < p->p_inc)

			vars->p_drop = ~0;

		vars->blue_timer = now;

	}

	vars->dropping = true;

	vars->drop_next = now;

		u32 p_drop = vars->p_drop;



		up = !p_drop;

		p_drop += p->p_inc;

		if (p_drop < p->p_inc)

			p_drop = ~0;

		WRITE_ONCE(vars->p_drop, p_drop);

		WRITE_ONCE(vars->blue_timer, now);

	}

	WRITE_ONCE(vars->dropping, true);

	WRITE_ONCE(vars->drop_next, now);

	if (!vars->count)

		vars->count = 1;

		WRITE_ONCE(vars->count, 1);



	return up;

}
@@ -475,20 +478,20 @@ static bool cobalt_queue_empty(struct cobalt_vars *vars, 
	if (vars->p_drop &&

	    ktime_to_ns(ktime_sub(now, vars->blue_timer)) > p->target) {

		if (vars->p_drop < p->p_dec)

			vars->p_drop = 0;

			WRITE_ONCE(vars->p_drop, 0);

		else

			vars->p_drop -= p->p_dec;

		vars->blue_timer = now;

			WRITE_ONCE(vars->p_drop, vars->p_drop - p->p_dec);

		WRITE_ONCE(vars->blue_timer, now);

		down = !vars->p_drop;

	}

	vars->dropping = false;

	WRITE_ONCE(vars->dropping, false);



	if (vars->count && ktime_to_ns(ktime_sub(now, vars->drop_next)) >= 0) {

		vars->count--;

		cobalt_invsqrt(vars);

		vars->drop_next = cobalt_control(vars->drop_next,

						 p->interval,

						 vars->rec_inv_sqrt);

		WRITE_ONCE(vars->count, vars->count - 1);

		cobalt_invsqrt(vars, vars->count);

		WRITE_ONCE(vars->drop_next,

			   cobalt_control(vars->drop_next, p->interval,

					  vars->rec_inv_sqrt));

	}



	return down;
@@ -507,6 +510,7 @@ static enum qdisc_drop_reason cobalt_should_drop(struct cobalt_vars *vars, 
	bool next_due, over_target;

	ktime_t schedule;

	u64 sojourn;

	u32 count;



/* The 'schedule' variable records, in its sign, whether 'now' is before or

 * after 'drop_next'.  This allows 'drop_next' to be updated before the next
@@ -528,21 +532,22 @@ static enum qdisc_drop_reason cobalt_should_drop(struct cobalt_vars *vars, 
	over_target = sojourn > p->target &&

		      sojourn > p->mtu_time * bulk_flows * 2 &&

		      sojourn > p->mtu_time * 4;

	next_due = vars->count && ktime_to_ns(schedule) >= 0;

	count = vars->count;

	next_due = count && ktime_to_ns(schedule) >= 0;



	vars->ecn_marked = false;



	if (over_target) {

		if (!vars->dropping) {

			vars->dropping = true;

			vars->drop_next = cobalt_control(now,

							 p->interval,

							 vars->rec_inv_sqrt);

			WRITE_ONCE(vars->dropping, true);

			WRITE_ONCE(vars->drop_next,

				   cobalt_control(now, p->interval,

						  vars->rec_inv_sqrt));

		}

		if (!vars->count)

			vars->count = 1;

		if (!count)

			count = 1;

	} else if (vars->dropping) {

		vars->dropping = false;

		WRITE_ONCE(vars->dropping, false);

	}



	if (next_due && vars->dropping) {
@@ -550,23 +555,23 @@ static enum qdisc_drop_reason cobalt_should_drop(struct cobalt_vars *vars, 
		if (!(vars->ecn_marked = INET_ECN_set_ce(skb)))

			reason = QDISC_DROP_CONGESTED;



		vars->count++;

		if (!vars->count)

			vars->count--;

		cobalt_invsqrt(vars);

		vars->drop_next = cobalt_control(vars->drop_next,

						 p->interval,

						 vars->rec_inv_sqrt);

		count++;

		if (!count)

			count--;

		cobalt_invsqrt(vars, count);

		WRITE_ONCE(vars->drop_next,

			   cobalt_control(vars->drop_next, p->interval,

					  vars->rec_inv_sqrt));

		schedule = ktime_sub(now, vars->drop_next);

	} else {

		while (next_due) {

			vars->count--;

			cobalt_invsqrt(vars);

			vars->drop_next = cobalt_control(vars->drop_next,

							 p->interval,

							 vars->rec_inv_sqrt);

			count--;

			cobalt_invsqrt(vars, count);

			WRITE_ONCE(vars->drop_next,

				   cobalt_control(vars->drop_next, p->interval,

						  vars->rec_inv_sqrt));

			schedule = ktime_sub(now, vars->drop_next);

			next_due = vars->count && ktime_to_ns(schedule) >= 0;

			next_due = count && ktime_to_ns(schedule) >= 0;

		}

	}
@@ -575,11 +580,12 @@ static enum qdisc_drop_reason cobalt_should_drop(struct cobalt_vars *vars, 
	    get_random_u32() < vars->p_drop)

		reason = QDISC_DROP_FLOOD_PROTECTION;



	WRITE_ONCE(vars->count, count);

	/* Overload the drop_next field as an activity timeout */

	if (!vars->count)

		vars->drop_next = ktime_add_ns(now, p->interval);

	if (!count)

		WRITE_ONCE(vars->drop_next, ktime_add_ns(now, p->interval));

	else if (ktime_to_ns(schedule) > 0 && reason == QDISC_DROP_UNSPEC)

		vars->drop_next = now;

		WRITE_ONCE(vars->drop_next, now);



	return reason;

}
@@ -1924,7 +1930,7 @@ static s32 cake_enqueue(struct sk_buff *skb, struct Qdisc *sch, 
		flow->set = CAKE_SET_SPARSE;

		WRITE_ONCE(b->sparse_flow_count, b->sparse_flow_count + 1);



		flow->deficit = cake_get_flow_quantum(b, flow, q->config->flow_mode);

		WRITE_ONCE(flow->deficit, cake_get_flow_quantum(b, flow, q->config->flow_mode));

	} else if (flow->set == CAKE_SET_SPARSE_WAIT) {

		/* this flow was empty, accounted as a sparse flow, but actually

		 * in the bulk rotation.
@@ -2166,7 +2172,8 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch) 
			}

		}



		flow->deficit += cake_get_flow_quantum(b, flow, q->config->flow_mode);

		WRITE_ONCE(flow->deficit,

			   flow->deficit + cake_get_flow_quantum(b, flow, q->config->flow_mode));

		list_move_tail(&flow->flowchain, &b->old_flows);



		goto retry;
@@ -2232,7 +2239,7 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch) 
		if (q->config->rate_flags & CAKE_FLAG_INGRESS) {

			len = cake_advance_shaper(q, b, skb,

						  now, true);

			flow->deficit -= len;

			WRITE_ONCE(flow->deficit, flow->deficit - len);

			b->tin_deficit -= len;

		}

		WRITE_ONCE(flow->dropped, flow->dropped + 1);
@@ -2259,7 +2266,7 @@ static struct sk_buff *cake_dequeue(struct Qdisc *sch) 
			     delay < b->base_delay ? 2 : 8));



	len = cake_advance_shaper(q, b, skb, now, false);

	flow->deficit -= len;

	WRITE_ONCE(flow->deficit, flow->deficit - len);

	b->tin_deficit -= len;



	if (ktime_after(q->time_next_packet, now) && sch->q.qlen) {
@@ -3153,6 +3160,8 @@ static int cake_dump_class_stats(struct Qdisc *sch, unsigned long cl, 
		return -1;

	if (flow) {

		ktime_t now = ktime_get();

		bool dropping;

		u32 p_drop;



		stats = nla_nest_start_noflag(d->skb, TCA_STATS_APP);

		if (!stats)
@@ -3167,21 +3176,23 @@ static int cake_dump_class_stats(struct Qdisc *sch, unsigned long cl, 
			goto nla_put_failure;			       \

	} while (0)



		PUT_STAT_S32(DEFICIT, flow->deficit);

		PUT_STAT_U32(DROPPING, flow->cvars.dropping);

		PUT_STAT_U32(COBALT_COUNT, flow->cvars.count);

		PUT_STAT_U32(P_DROP, flow->cvars.p_drop);

		if (flow->cvars.p_drop) {

		PUT_STAT_S32(DEFICIT, READ_ONCE(flow->deficit));

		dropping = READ_ONCE(flow->cvars.dropping);

		PUT_STAT_U32(DROPPING, dropping);

		PUT_STAT_U32(COBALT_COUNT, READ_ONCE(flow->cvars.count));

		p_drop = READ_ONCE(flow->cvars.p_drop);

		PUT_STAT_U32(P_DROP, p_drop);

		if (p_drop) {

			PUT_STAT_S32(BLUE_TIMER_US,

				     ktime_to_us(

					     ktime_sub(now,

						       flow->cvars.blue_timer)));

						       READ_ONCE(flow->cvars.blue_timer))));

		}

		if (flow->cvars.dropping) {

		if (dropping) {

			PUT_STAT_S32(DROP_NEXT_US,

				     ktime_to_us(

					     ktime_sub(now,

						       flow->cvars.drop_next)));

						       READ_ONCE(flow->cvars.drop_next))));

		}



		if (nla_nest_end(d->skb, stats) < 0)