[PATCH net v1] net: phy: Fix race condition on link status change

* [PATCH net v1] net: phy: Fix race condition on link status change
@ 2022-05-05 20:32 Francesco Dolcini
  2022-05-05 22:20 ` Andrew Lunn
  0 siblings, 1 reply; 2+ messages in thread
From: Francesco Dolcini @ 2022-05-05 20:32 UTC (permalink / raw)
  To: Andrew Lunn, Heiner Kallweit, Russell King, Joakim Zhang
  Cc: Francesco Dolcini, David S. Miller, Eric Dumazet, Jakub Kicinski,
	Paolo Abeni, netdev, stable

This fixes the following error caused by a race condition between
phydev->adjust_link() and a MDIO transaction in the phy interrupt
handler. The issue was reproduced with the ethernet FEC driver and a
micrel KSZ9031 phy.

[  146.195696] fec 2188000.ethernet eth0: MDIO read timeout
[  146.201779] ------------[ cut here ]------------
[  146.206671] WARNING: CPU: 0 PID: 571 at drivers/net/phy/phy.c:942 phy_error+0x24/0x6c
[  146.214744] Modules linked in: bnep imx_vdoa imx_sdma evbug
[  146.220640] CPU: 0 PID: 571 Comm: irq/128-2188000 Not tainted 5.18.0-rc3-00080-gd569e86915b7 #9
[  146.229563] Hardware name: Freescale i.MX6 Quad/DualLite (Device Tree)
[  146.236257]  unwind_backtrace from show_stack+0x10/0x14
[  146.241640]  show_stack from dump_stack_lvl+0x58/0x70
[  146.246841]  dump_stack_lvl from __warn+0xb4/0x24c
[  146.251772]  __warn from warn_slowpath_fmt+0x5c/0xd4
[  146.256873]  warn_slowpath_fmt from phy_error+0x24/0x6c
[  146.262249]  phy_error from kszphy_handle_interrupt+0x40/0x48
[  146.268159]  kszphy_handle_interrupt from irq_thread_fn+0x1c/0x78
[  146.274417]  irq_thread_fn from irq_thread+0xf0/0x1dc
[  146.279605]  irq_thread from kthread+0xe4/0x104
[  146.284267]  kthread from ret_from_fork+0x14/0x28
[  146.289164] Exception stack(0xe6fa1fb0 to 0xe6fa1ff8)
[  146.294448] 1fa0:                                     00000000 00000000 00000000 00000000
[  146.302842] 1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[  146.311281] 1fe0: 00000000 00000000 00000000 00000000 00000013 00000000
[  146.318262] irq event stamp: 12325
[  146.321780] hardirqs last  enabled at (12333): [<c01984c4>] __up_console_sem+0x50/0x60
[  146.330013] hardirqs last disabled at (12342): [<c01984b0>] __up_console_sem+0x3c/0x60
[  146.338259] softirqs last  enabled at (12324): [<c01017f0>] __do_softirq+0x2c0/0x624
[  146.346311] softirqs last disabled at (12319): [<c01300ac>] __irq_exit_rcu+0x138/0x178
[  146.354447] ---[ end trace 0000000000000000 ]---

With the FEC driver phydev->adjust_link() calls fec_enet_adjust_link()
calls fec_stop()/fec_restart() and both these function reset and
temporary disable the FEC disrupting any MII transaction that
could be happening at the same time.

fec_enet_adjust_link() and phy_read() can be running at the same time
when we have one additional interrupt before the phy_state_machine() is
able to terminate.

Thread 1 (phylib WQ)       | Thread 2 (phy interrupt)
                           |
                           | phy_interrupt()            <-- PHY IRQ
	                   |  handle_interrupt()
	                   |   phy_read()
	                   |   phy_trigger_machine()
	                   |    --> schedule phylib WQ
                           |
	                   |
phy_state_machine()        |
 phy_check_link_status()   |
  phy_link_change()        |
   phydev->adjust_link()   |
    fec_enet_adjust_link() |
     --> FEC reset         | phy_interrupt()            <-- PHY IRQ
	                   |  phy_read()
	 	           |

Fix this by acquiring the phydev lock in phy_interrupt().

Link: https://lore.kernel.org/all/20220422152612.GA510015@francesco-nb.int.toradex.com/
cc: <stable@vger.kernel.org>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
---
 drivers/net/phy/phy.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/phy/phy.c b/drivers/net/phy/phy.c
index beb2b66da132..f122026c4682 100644
--- a/drivers/net/phy/phy.c
+++ b/drivers/net/phy/phy.c
@@ -970,8 +970,13 @@ static irqreturn_t phy_interrupt(int irq, void *phy_dat)
 {
 	struct phy_device *phydev = phy_dat;
 	struct phy_driver *drv = phydev->drv;
+	irqreturn_t ret;
 
-	return drv->handle_interrupt(phydev);
+	mutex_lock(&phydev->lock);
+	ret = drv->handle_interrupt(phydev);
+	mutex_unlock(&phydev->lock);
+
+	return ret;
 }
 
 /**
-- 
2.25.1


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