netdev - Re: [PATCH net v2] phy: mscc: Stop taking ts_lock for tx

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Message-ID: <20250902065047.shz6bkyfewleluzp@DEN-DL-M31836.microchip.com>
Date: Tue, 2 Sep 2025 08:50:47 +0200
From: Horatiu Vultur <horatiu.vultur@...rochip.com>
To: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
CC: <andrew@...n.ch>, <hkallweit1@...il.com>, <linux@...linux.org.uk>,
	<davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
	<pabeni@...hat.com>, <richardcochran@...il.com>, <vladimir.oltean@....com>,
	<viro@...iv.linux.org.uk>, <atenart@...nel.org>,
	<quentin.schulz@...tlin.com>, <netdev@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net v2] phy: mscc: Stop taking ts_lock for tx_queue and
 use its own lock

The 09/01/2025 11:19, Vadim Fedorenko wrote:

Hi Vadim,

> 
> On 01/09/2025 10:23, Horatiu Vultur wrote:
> > When transmitting a PTP frame which is timestamp using 2 step, the
> > following warning appears if CONFIG_PROVE_LOCKING is enabled:
> > =============================
> > [ BUG: Invalid wait context ]
> > 6.17.0-rc1-00326-ge6160462704e #427 Not tainted
> > -----------------------------
> > ptp4l/119 is trying to lock:
> > c2a44ed4 (&vsc8531->ts_lock){+.+.}-{3:3}, at: vsc85xx_txtstamp+0x50/0xac
> > other info that might help us debug this:
> > context-{4:4}
> > 4 locks held by ptp4l/119:
> >   #0: c145f068 (rcu_read_lock_bh){....}-{1:2}, at: __dev_queue_xmit+0x58/0x1440
> >   #1: c29df974 (dev->qdisc_tx_busylock ?: &qdisc_tx_busylock){+...}-{2:2}, at: __dev_queue_xmit+0x5c4/0x1440
> >   #2: c2aaaad0 (_xmit_ETHER#2){+.-.}-{2:2}, at: sch_direct_xmit+0x108/0x350
> >   #3: c2aac170 (&lan966x->tx_lock){+.-.}-{2:2}, at: lan966x_port_xmit+0xd0/0x350
> > stack backtrace:
> > CPU: 0 UID: 0 PID: 119 Comm: ptp4l Not tainted 6.17.0-rc1-00326-ge6160462704e #427 NONE
> > Hardware name: Generic DT based system
> > Call trace:
> >   unwind_backtrace from show_stack+0x10/0x14
> >   show_stack from dump_stack_lvl+0x7c/0xac
> >   dump_stack_lvl from __lock_acquire+0x8e8/0x29dc
> >   __lock_acquire from lock_acquire+0x108/0x38c
> >   lock_acquire from __mutex_lock+0xb0/0xe78
> >   __mutex_lock from mutex_lock_nested+0x1c/0x24
> >   mutex_lock_nested from vsc85xx_txtstamp+0x50/0xac
> >   vsc85xx_txtstamp from lan966x_fdma_xmit+0xd8/0x3a8
> >   lan966x_fdma_xmit from lan966x_port_xmit+0x1bc/0x350
> >   lan966x_port_xmit from dev_hard_start_xmit+0xc8/0x2c0
> >   dev_hard_start_xmit from sch_direct_xmit+0x8c/0x350
> >   sch_direct_xmit from __dev_queue_xmit+0x680/0x1440
> >   __dev_queue_xmit from packet_sendmsg+0xfa4/0x1568
> >   packet_sendmsg from __sys_sendto+0x110/0x19c
> >   __sys_sendto from sys_send+0x18/0x20
> >   sys_send from ret_fast_syscall+0x0/0x1c
> > Exception stack(0xf0b05fa8 to 0xf0b05ff0)
> > 5fa0:                   00000001 0000000e 0000000e 0004b47a 0000003a 00000000
> > 5fc0: 00000001 0000000e 00000000 00000121 0004af58 00044874 00000000 00000000
> > 5fe0: 00000001 bee9d420 00025a10 b6e75c7c
> > 
> > So, instead of using the ts_lock for tx_queue, use the spinlock that
> > skb_buff_head has.
> > 
> > Fixes: 7d272e63e0979d ("net: phy: mscc: timestamping and PHC support")
> > Signed-off-by: Horatiu Vultur <horatiu.vultur@...rochip.com>
> > 
> > ---
> > v1->v2:
> > - initialize tx_queue in ptp_probe
> > - purge the tx_queue when the driver is removed or when TX timestamping
> >    is OFF
> > ---
> >   drivers/net/phy/mscc/mscc_ptp.c | 16 +++++++---------
> >   1 file changed, 7 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/net/phy/mscc/mscc_ptp.c b/drivers/net/phy/mscc/mscc_ptp.c
> > index 72847320cb652..e866a1d865f8b 100644
> > --- a/drivers/net/phy/mscc/mscc_ptp.c
> > +++ b/drivers/net/phy/mscc/mscc_ptp.c
> > @@ -461,7 +461,7 @@ static void vsc85xx_dequeue_skb(struct vsc85xx_ptp *ptp)
> >               return;
> > 
> >       while (len--) {
> > -             skb = __skb_dequeue(&ptp->tx_queue);
> > +             skb = skb_dequeue(&ptp->tx_queue);
> 
> Now as you switched to use spinlock of tx_queue, it is technically
> correct to change skb_queue_len(&ptp->tx_queue) to
> skb_queue_len_lockless(&ptp->tx_queue) a couple of lines above this
> chunk.

I will update this in the next version.
Thanks!

> 
> Otherwise LGTM, once skb_queue_len fixed you can add
> 
> Reviewed-by: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
> 
> 
> Thanks!
> 
> >               if (!skb)
> >                       return;
> > 
> > @@ -486,7 +486,7 @@ static void vsc85xx_dequeue_skb(struct vsc85xx_ptp *ptp)
> >                * packet in the FIFO right now, reschedule it for later
> >                * packets.
> >                */
> > -             __skb_queue_tail(&ptp->tx_queue, skb);
> > +             skb_queue_tail(&ptp->tx_queue, skb);
> 

-- 
/Horatiu