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Message-Id: <20200707152204.10314-1-john.ogness@linutronix.de>
Date: Tue, 7 Jul 2020 17:28:04 +0206
From: John Ogness <john.ogness@...utronix.de>
To: "David S . Miller" <davem@...emloft.net>
Cc: Jakub Kicinski <kuba@...nel.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Thomas Gleixner <tglx@...utronix.de>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH] 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@...utronix.de>
---
patch against v5.8-rc4
net/packet/af_packet.c | 20 ++++++++++----------
net/packet/internal.h | 2 +-
2 files changed, 11 insertions(+), 11 deletions(-)
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 29bd405adbbd..dd1eec2dd6ef 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -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);
}
diff --git a/net/packet/internal.h b/net/packet/internal.h
index 907f4cd2a718..fd41ecb7f605 100644
--- a/net/packet/internal.h
+++ b/net/packet/internal.h
@@ -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)
--
2.20.1
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