net: af_packet: remove last_kactive_blk_num field

kactive_blk_num (K) is only incremented on block close.
In timer callback prb_retire_rx_blk_timer_expired, except delete_blk_timer
is true, last_kactive_blk_num (L) is set to match kactive_blk_num (K) in
all cases. L is also set to match K in prb_open_block.
The only case K not equal to L is when scheduled by tpacket_rcv
and K is just incremented on block close but no new block could be opened,
so that it does not call prb_open_block in prb_dispatch_next_block.
This patch modifies the prb_retire_rx_blk_timer_expired function by simply
removing the check for L == K. This patch just provides another checkpoint
to thaw the might-be-frozen block in any case. It doesn't have any effect
because __packet_lookup_frame_in_block() has the same logic and does it
again without this patch when detecting the ring is frozen. The patch only
advances checking the status of the ring.

Suggested-by: Willem de Bruijn <[email protected]>
Reviewed-by: Willem de Bruijn <[email protected]>
Reviewed-by: Jason Xing <[email protected]>
Link: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Xin Zhao <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

Author: jackzxcui1989

net/packet/af_packet.c

@@ -669,7 +669,6 @@ static void init_prb_bdqc(struct packet_sock *po,
 	p1->knum_blocks	= req_u->req3.tp_block_nr;
 	p1->hdrlen = po->tp_hdrlen;
 	p1->version = po->tp_version;
-	p1->last_kactive_blk_num = 0;
 	po->stats.stats3.tp_freeze_q_cnt = 0;
 	if (req_u->req3.tp_retire_blk_tov)
 		p1->retire_blk_tov = req_u->req3.tp_retire_blk_tov;
@@ -693,7 +692,6 @@ static void _prb_refresh_rx_retire_blk_timer(struct tpacket_kbdq_core *pkc)
 {
 	mod_timer(&pkc->retire_blk_timer,
 			jiffies + pkc->tov_in_jiffies);
-	pkc->last_kactive_blk_num = pkc->kactive_blk_num;
 }
 
 /*
@@ -750,38 +748,36 @@ static void prb_retire_rx_blk_timer_expired(struct timer_list *t)
 		write_unlock(&pkc->blk_fill_in_prog_lock);
 	}
 
-	if (pkc->last_kactive_blk_num == pkc->kactive_blk_num) {
-		if (!frozen) {
-			if (!BLOCK_NUM_PKTS(pbd)) {
-				/* An empty block. Just refresh the timer. */
-				goto refresh_timer;
-			}
-			prb_retire_current_block(pkc, po, TP_STATUS_BLK_TMO);
-			if (!prb_dispatch_next_block(pkc, po))
-				goto refresh_timer;
-			else
-				goto out;
+	if (!frozen) {
+		if (!BLOCK_NUM_PKTS(pbd)) {
+			/* An empty block. Just refresh the timer. */
+			goto refresh_timer;
+		}
+		prb_retire_current_block(pkc, po, TP_STATUS_BLK_TMO);
+		if (!prb_dispatch_next_block(pkc, po))
+			goto refresh_timer;
+		else
+			goto out;
+	} else {
+		/* Case 1. Queue was frozen because user-space was
+		 * lagging behind.
+		 */
+		if (prb_curr_blk_in_use(pbd)) {
+			/*
+			 * Ok, user-space is still behind.
+			 * So just refresh the timer.
+			 */
+			goto refresh_timer;
 		} else {
-			/* Case 1. Queue was frozen because user-space was
-			 *	   lagging behind.
+			/* Case 2. queue was frozen,user-space caught up,
+			 * now the link went idle && the timer fired.
+			 * We don't have a block to close.So we open this
+			 * block and restart the timer.
+			 * opening a block thaws the queue,restarts timer
+			 * Thawing/timer-refresh is a side effect.
 			 */
-			if (prb_curr_blk_in_use(pbd)) {
-				/*
-				 * Ok, user-space is still behind.
-				 * So just refresh the timer.
-				 */
-				goto refresh_timer;
-			} else {
-			       /* Case 2. queue was frozen,user-space caught up,
-				* now the link went idle && the timer fired.
-				* We don't have a block to close.So we open this
-				* block and restart the timer.
-				* opening a block thaws the queue,restarts timer
-				* Thawing/timer-refresh is a side effect.
-				*/
-				prb_open_block(pkc, pbd);
-				goto out;
-			}
+			prb_open_block(pkc, pbd);
+			goto out;
 		}
 	}
 

net/packet/internal.h

@@ -24,12 +24,6 @@ struct tpacket_kbdq_core {
 	unsigned short	kactive_blk_num;
 	unsigned short	blk_sizeof_priv;
 
-	/* last_kactive_blk_num:
-	 * trick to see if user-space has caught up
-	 * in order to avoid refreshing timer when every single pkt arrives.
-	 */
-	unsigned short	last_kactive_blk_num;
-
 	char		*pkblk_start;
 	char		*pkblk_end;
 	int		kblk_size;