FAILED: patch "[PATCH] net: phy: Fix race condition on link status change" failed to apply to 4.14-stable tree

The patch below does not apply to the 4.14-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 91a7cda1f4b8bdf770000a3b60640576dafe0cec Mon Sep 17 00:00:00 2001
From: Francesco Dolcini <[email protected]>
Date: Fri, 6 May 2022 08:08:15 +0200
Subject: [PATCH] net: phy: Fix race condition on link status change

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().

index beb2b66da132..f122026c4682 100644
@@ -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;
 }
 
 /**