net: phy: Deal with unbound PHY driver in phy_attached_print()

Priit reported that stmmac was crashing with the trace below. This is because
phy_attached_print() is called too early right after the PHY device has been
found, but before it has a driver attached, since that is only done in
phy_probe() which occurs later.

Fix this by dealing with a possibly NULL phydev->drv point since that can
happen here, but could also happen if we voluntarily did an unbind of the
PHY device with the PHY driver.

sun7i-dwmac 1c50000.ethernet: PTP uses main clock
sun7i-dwmac 1c50000.ethernet: no reset control found
sun7i-dwmac 1c50000.ethernet: no regulator found
sun7i-dwmac 1c50000.ethernet: Ring mode enabled
sun7i-dwmac 1c50000.ethernet: DMA HW capability register supported
sun7i-dwmac 1c50000.ethernet: Normal descriptors
libphy: stmmac: probed
Unable to handle kernel NULL pointer dereference at virtual address 00000048
pgd = c0004000
[00000048] *pgd=00000000
Internal error: Oops: 5 [#1] SMP ARM
Modules linked in:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.13.0-rc6-00318-g0065bd7fa384 #1
Hardware name: Allwinner sun7i (A20) Family
task: ee868000 task.stack: ee85c000
PC is at phy_attached_print+0x1c/0x8c
LR is at stmmac_mdio_register+0x12c/0x200
pc : [<c04510ac>]    lr : [<c045e6b4>]    psr: 60000013
sp : ee85ddc8  ip : 00000000  fp : c07dfb5c
r10: ee981210  r9 : 00000001  r8 : eea73000
r7 : eeaa6dd0  r6 : eeb49800  r5 : 00000000  r4 : 00000000
r3 : 00000000  r2 : 00000000  r1 : 00000000  r0 : eeb49800
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
Control: 10c5387d  Table: 4000406a  DAC: 00000051
Process swapper/0 (pid: 1, stack limit = 0xee85c210)
Stack: (0xee85ddc8 to 0xee85e000)
ddc0:                   00000000 00000002 eeb49400 eea72000 00000000 eeb49400
dde0: c045e6b4 00000000 ffffffff eeab0810 00000000 c08051f8 ee9292c0 c016d480
de00: eea725c0 eea73000 eea72000 00000001 eea726c0 c0457d0c 00000040 00000020
de20: 00000000 c045b850 00000001 00000000 ee981200 eeab0810 eeaa6ed0 ee981210
de40: 00000000 c094a4a0 00000000 c0465180 eeaa7550 f08d0000 c9ffb90c 00000032
de60: fffffffa 00000032 ee981210 ffffffed c0a46620 fffffdfb c0a46620 c03f7be8
de80: ee981210 c0a9a388 00000000 00000000 c0a46620 c03f63e0 ee981210 c0a46620
dea0: ee981244 00000000 00000007 000000c6 c094a4a0 c03f6534 00000000 c0a46620
dec0: c03f6490 c03f49ec ee828a58 ee9217b4 c0a46620 eeaa4b00 c0a43230 c03f59fc
dee0: c08051f8 c094a49c c0a46620 c0a46620 00000000 c091c668 c093783c c03f6dfc
df00: ffffe000 00000000 c091c668 c010177c eefe0938 eefe0935 c085e200 000000c6
df20: 00000005 c0136bc8 60000013 c080b3a4 00000006 00000006 c07ce7b4 00000000
df40: c07d7ddc c07cef28 eefe0938 eefe093e c0a0b2f0 c0a641c0 c0a641c0 c0a641c0
df60: c0937834 00000007 000000c6 c094a4a0 00000000 c0900d88 00000006 00000006
df80: 00000000 c09005a8 00000000 c060ecf4 00000000 00000000 00000000 00000000
dfa0: 00000000 c060ecfc 00000000 c0107738 00000000 00000000 00000000 00000000
dfc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
dfe0: 00000000 00000000 00000000 00000000 00000013 00000000 ffdeffff ffffffff
[<c04510ac>] (phy_attached_print) from [<c045e6b4>] (stmmac_mdio_register+0x12c/0x200)
[<c045e6b4>] (stmmac_mdio_register) from [<c045b850>] (stmmac_dvr_probe+0x850/0x96c)
[<c045b850>] (stmmac_dvr_probe) from [<c0465180>] (sun7i_gmac_probe+0x120/0x180)
[<c0465180>] (sun7i_gmac_probe) from [<c03f7be8>] (platform_drv_probe+0x50/0xac)
[<c03f7be8>] (platform_drv_probe) from [<c03f63e0>] (driver_probe_device+0x234/0x2e4)
[<c03f63e0>] (driver_probe_device) from [<c03f6534>] (__driver_attach+0xa4/0xa8)
[<c03f6534>] (__driver_attach) from [<c03f49ec>] (bus_for_each_dev+0x4c/0x9c)
[<c03f49ec>] (bus_for_each_dev) from [<c03f59fc>] (bus_add_driver+0x190/0x214)
[<c03f59fc>] (bus_add_driver) from [<c03f6dfc>] (driver_register+0x78/0xf4)
[<c03f6dfc>] (driver_register) from [<c010177c>] (do_one_initcall+0x44/0x168)
[<c010177c>] (do_one_initcall) from [<c0900d88>] (kernel_init_freeable+0x144/0x1d0)
[<c0900d88>] (kernel_init_freeable) from [<c060ecfc>] (kernel_init+0x8/0x110)
[<c060ecfc>] (kernel_init) from [<c0107738>] (ret_from_fork+0x14/0x3c)
Code: e59021c8 e59d401c e590302c e3540000 (e5922048)
---[ end trace 39ae87c7923562d0 ]---
Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b

Tested-By: Priit Laes <plaes@plaes.org>
Fixes: fbca164776e4 ("net: stmmac: Use the right logging function in stmmac_mdio_register")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/phy/phy_device.c

@@ -864,15 +864,17 @@ EXPORT_SYMBOL(phy_attached_info);
 #define ATTACHED_FMT "attached PHY driver [%s] (mii_bus:phy_addr=%s, irq=%d)"
 void phy_attached_print(struct phy_device *phydev, const char *fmt, ...)
 {
+	const char *drv_name = phydev->drv ? phydev->drv->name : "unbound";
+
 	if (!fmt) {
 		dev_info(&phydev->mdio.dev, ATTACHED_FMT "\n",
-			 phydev->drv->name, phydev_name(phydev),
+			 drv_name, phydev_name(phydev),
 			 phydev->irq);
 	} else {
 		va_list ap;
 
 		dev_info(&phydev->mdio.dev, ATTACHED_FMT,
-			 phydev->drv->name, phydev_name(phydev),
+			 drv_name, phydev_name(phydev),
 			 phydev->irq);
 
 		va_start(ap, fmt);