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af_packet: TPACKET_V3: replace busy-wait loop 

A busy-wait loop is used to implement waiting for bits to be copied
from the skb to the kernel buffer before retiring a block. This is
a problem on PREEMPT_RT because the copying task could be preempted
by the busy-waiting task and thus live lock in the busy-wait loop.

Replace the busy-wait logic with an rwlock_t. This provides lockdep
coverage and makes the code RT ready.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
John Ogness 2020-07-07 17:28:04 +02:06 committed by Jakub Kicinski
parent 999cf8aeb6
commit 632ca50f2c
2 changed files with 11 additions and 11 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
net/packet/af_packet.c
View File

@ -593,6 +593,7 @@ static void init_prb_bdqc(struct packet_sock *po,
req_u->req3.tp_block_size);
p1->tov_in_jiffies = msecs_to_jiffies(p1->retire_blk_tov);
p1->blk_sizeof_priv = req_u->req3.tp_sizeof_priv;
rwlock_init(&p1->blk_fill_in_prog_lock);
p1->max_frame_len = p1->kblk_size - BLK_PLUS_PRIV(p1->blk_sizeof_priv);
prb_init_ft_ops(p1, req_u);
@ -659,10 +660,9 @@ static void prb_retire_rx_blk_timer_expired(struct timer_list *t)
*
*/
if (BLOCK_NUM_PKTS(pbd)) {
while (atomic_read(&pkc->blk_fill_in_prog)) {
/* Waiting for skb_copy_bits to finish... */
cpu_relax();
}
/* Waiting for skb_copy_bits to finish... */
write_lock(&pkc->blk_fill_in_prog_lock);
write_unlock(&pkc->blk_fill_in_prog_lock);
}
if (pkc->last_kactive_blk_num == pkc->kactive_blk_num) {
@ -921,10 +921,9 @@ static void prb_retire_current_block(struct tpacket_kbdq_core *pkc,
* the timer-handler already handled this case.
*/
if (!(status & TP_STATUS_BLK_TMO)) {
while (atomic_read(&pkc->blk_fill_in_prog)) {
/* Waiting for skb_copy_bits to finish... */
cpu_relax();
}
/* Waiting for skb_copy_bits to finish... */
write_lock(&pkc->blk_fill_in_prog_lock);
write_unlock(&pkc->blk_fill_in_prog_lock);
}
prb_close_block(pkc, pbd, po, status);
return;
@ -944,7 +943,8 @@ static int prb_queue_frozen(struct tpacket_kbdq_core *pkc)
static void prb_clear_blk_fill_status(struct packet_ring_buffer *rb)
{
struct tpacket_kbdq_core *pkc = GET_PBDQC_FROM_RB(rb);
atomic_dec(&pkc->blk_fill_in_prog);
read_unlock(&pkc->blk_fill_in_prog_lock);
}
static void prb_fill_rxhash(struct tpacket_kbdq_core *pkc,
@ -998,7 +998,7 @@ static void prb_fill_curr_block(char *curr,
pkc->nxt_offset += TOTAL_PKT_LEN_INCL_ALIGN(len);
BLOCK_LEN(pbd) += TOTAL_PKT_LEN_INCL_ALIGN(len);
BLOCK_NUM_PKTS(pbd) += 1;
atomic_inc(&pkc->blk_fill_in_prog);
read_lock(&pkc->blk_fill_in_prog_lock);
prb_run_all_ft_ops(pkc, ppd);
}

2
net/packet/internal.h
View File

@ -39,7 +39,7 @@ struct tpacket_kbdq_core {
char *nxt_offset;
struct sk_buff *skb;
atomic_t blk_fill_in_prog;
rwlock_t blk_fill_in_prog_lock;
/* Default is set to 8ms */
#define DEFAULT_PRB_RETIRE_TOV (8)