phy: Add null check before calling adjust link

Issue:
phydev->adjust_link can be NULL in case of phy which
generates link down interrupt after phy_stop is called.
This interrupt causes a race condition, with adjust link
being set to NULL when we get an interrupt and simultaneously
phy is getting disconnected.

[ 2683.554983] libphy: Calling adjust link, up = 0
[ 2683.559652] ether_adjust_link, 1100, disconnect
[ 2683.564750] nvethernet 6810000.ethernet eth2: Link is Down
[ 2683.571863] phy_state_machine Calling phy suspend
[ 2683.577192] Calling phy disconnect from close
[ 2683.580703] Intr handler, state machine
[ 2683.586079] libphy: Calling adjust link, up = 0
[ 2683.586108] libphy: phy_disconnect adjust link = NULL
[ 2683.590749] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
[ 2683.595942] libphy: phy_detach, 1667
[ 2683.604958] Mem abort info:
[ 2683.604959]   ESR = 0x86000004
[ 2683.604961]   EC = 0x21: IABT (current EL), IL = 32 bits
[ 2683.608629] libphy: phy_detach, 1671
[ 2683.608630] libphy: phy_detach, 1674
[ 2683.611496]   SET = 0, FnV = 0
[ 2683.611498]   EA = 0, S1PTW = 0
[ 2683.633773] user pgtable: 4k pages, 48-bit VAs, pgdp=0000000107bf0000
[ 2683.640380] [0000000000000000] pgd=0000000000000000, p4d=0000000000000000
[ 2683.647372] Internal error: Oops: 86000004 [OE4T#1] PREEMPT SMP
[ 2683.653093] Modules linked in:
[ 2683.656235] CPU: 6 PID: 1219 Comm: kworker/u16:0 Tainted: G        W         5.10.120-tegra OE4T#10
[ 2683.665174] Hardware name: Unknown Jetson AGX Orin/Jetson AGX Orin, BIOS 0.0-ff9214ce 12/20/2022
[ 2683.674218] Workqueue: events_power_efficient phy_state_machine
[ 2683.680299] pstate: 60c00009 (nZCv daif +PAN +UAO -TCO BTYPE=--)
[ 2683.686467] pc : 0x0
[ 2683.688710] lr : phy_link_change+0x50/0xb0
[ 2683.692908] sp : ffff800016dc3d20
[ 2683.696303] x29: ffff800016dc3d20 x28: ffffb676a7a26000
[ 2683.701762] x27: ffff7513c014f470 x26: ffff7513c014f420
[ 2683.707218] x25: 0000000000000000 x24: ffff7513c7ebe800
[ 2683.712681] x23: ffff7513c6aa0000 x22: ffff7513c7ebecf8
[ 2683.718137] x21: 0000000000000000 x20: ffff7513c6aa0000
[ 2683.723593] x19: ffff7513c7ebe800 x18: 0000000000000010
[ 2683.729047] x17: 0000000000000000 x16: 0000000000000000
[ 2683.734507] x15: ffff7513c7f61470 x14: ffffffffffffffff
[ 2683.739958] x13: ffff800096dc3a17 x12: ffff800016dc3a1f
[ 2683.745419] x11: 0000000000000000 x10: ffffb676a7aa0aa0
[ 2683.750882] x9 : ffffb676a5bbba7c x8 : 20676e696c6c6143
[ 2683.756336] x7 : 203a79687062696c x6 : 000000000000000a
[ 2683.761788] x5 : 0000000000000002 x4 : 0000000000000000
[ 2683.767245] x3 : 00000000ffffffff x2 : 0000000000000000
[ 2683.772697] x1 : 0000000000000000 x0 : ffff7513c6aa0000
[ 2683.778154] Call trace:
[ 2683.780664]  0x0
[ 2683.782549]  phy_state_machine+0x194/0x260
[ 2683.786756]  process_one_work+0x1c4/0x4d0
[ 2683.790882]  worker_thread+0x54/0x430
[ 2683.794630]  kthread+0x148/0x180
[ 2683.797950]  ret_from_fork+0x10/0x34
[ 2683.801626] Code: bad PC value
[ 2683.804774] ---[ end trace e61974d923004c5a ]---
[ 2683.809521] Kernel panic - not syncing: Oops: Fatal exception
[ 2683.815741] Kernel Offset: 0x367695aa0000 from 0xffff800010000000
[ 2683.821999] PHYS_OFFSET: 0xffff8aed40000000
[ 2683.826290] CPU features: 0x081c0146,4a80aa38
[ 2683.830767] Memory Limit: none
[ 2683.833895] ---[ end Kernel panic - not syncing: Oops: Fatal exception ]---

Fix:
Add a null check before calling adjust_link callback.

Bug 3877272
Bug 3920560

Change-Id: I2843ff746a92bf23349628a02b32a4f16eea0ce1
Signed-off-by: Sushil Kumar Singh <[email protected]>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-5.10/+/2835744
(Cherry-picked from commit 009bebb6905f0d8040592007ce5f16f20212cf75)
Reviewed-on: https://git-master.nvidia.com/r/c/linux-5.10/+/2857069
Reviewed-by: Wayne Wang (SW-TEGRA) <[email protected]>
Reviewed-by: Bibek Basu <[email protected]>
GVS: Gerrit_Virtual_Submit <[email protected]>
Tested-by: Wayne Wang (SW-TEGRA) <[email protected]>

drivers/net/phy/phy_device.c

@@ -5,6 +5,7 @@
  * Author: Andy Fleming
  *
  * Copyright (c) 2004 Freescale Semiconductor, Inc.
+ * Copyright (c) 2023, NVIDIA CORPORATION.  All rights reserved.
  */
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
@@ -944,7 +945,10 @@ static void phy_link_change(struct phy_device *phydev, bool up)
 		netif_carrier_on(netdev);
 	else
 		netif_carrier_off(netdev);
-	phydev->adjust_link(netdev);
+
+	if (phydev->adjust_link)
+		phydev->adjust_link(netdev);
+
 	if (phydev->mii_ts && phydev->mii_ts->link_state)
 		phydev->mii_ts->link_state(phydev->mii_ts, phydev);
 }