KMSAN: uninit-value in asix_mdio_read

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    1e76a3e5 kmsan: replace __GFP_NO_KMSAN_SHADOW with kmsan_i..
git tree:       https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=10327cc3600000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f03c659d0830ab8d
dashboard link: https://syzkaller.appspot.com/bug?extid=a631ec9e717fb0423053
compiler:       clang version 9.0.0 (/home/glider/llvm/clang  
80fee25776c2fb61e74c1ecb1a523375c2500b69)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12e9a3db600000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=167fcefb600000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a631ec9e717fb0423053@xxxxxxxxxxxxxxxxxxxxxxxxx

asix 1-1:0.78 (unnamed net_device) (uninitialized): Failed to write reg  
index 0x0000: -71
asix 1-1:0.78 (unnamed net_device) (uninitialized): Failed to send software  
reset: ffffffb9
asix 1-1:0.78 (unnamed net_device) (uninitialized): Failed to write reg  
index 0x0000: -71
asix 1-1:0.78 (unnamed net_device) (uninitialized): Failed to enable  
software MII access
asix 1-1:0.78 (unnamed net_device) (uninitialized): Failed to read reg  
index 0x0000: -71
=====================================================
BUG: KMSAN: uninit-value in asix_mdio_bus_read+0xbc/0xe0  
drivers/net/usb/ax88172a.c:31
CPU: 0 PID: 2919 Comm: kworker/0:2 Not tainted 5.3.0-rc7+ #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Workqueue: usb_hub_wq hub_event
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x191/0x1f0 lib/dump_stack.c:113
 kmsan_report+0x13a/0x2b0 mm/kmsan/kmsan_report.c:108
 __msan_warning+0x73/0xe0 mm/kmsan/kmsan_instr.c:250
 asix_mdio_read+0x3e9/0x8f0 drivers/net/usb/asix_common.c:461
 asix_mdio_bus_read+0xbc/0xe0 drivers/net/usb/ax88172a.c:31
 __mdiobus_read+0x106/0x3d0 drivers/net/phy/mdio_bus.c:563
 mdiobus_read+0xbd/0x110 drivers/net/phy/mdio_bus.c:640
 get_phy_id drivers/net/phy/phy_device.c:785 [inline]
 get_phy_device+0x331/0x8a0 drivers/net/phy/phy_device.c:819
 mdiobus_scan+0x91/0x760 drivers/net/phy/mdio_bus.c:527
 __mdiobus_register+0x86d/0xca0 drivers/net/phy/mdio_bus.c:426
 ax88172a_init_mdio drivers/net/usb/ax88172a.c:105 [inline]
 ax88172a_bind+0xcc5/0xf80 drivers/net/usb/ax88172a.c:243
 usbnet_probe+0x10ae/0x3960 drivers/net/usb/usbnet.c:1722
 usb_probe_interface+0xd19/0x1310 drivers/usb/core/driver.c:361
 really_probe+0x1373/0x1dc0 drivers/base/dd.c:552
 driver_probe_device+0x1ba/0x510 drivers/base/dd.c:709
 __device_attach_driver+0x5b8/0x790 drivers/base/dd.c:816
 bus_for_each_drv+0x28e/0x3b0 drivers/base/bus.c:454
 __device_attach+0x489/0x750 drivers/base/dd.c:882
 device_initial_probe+0x4a/0x60 drivers/base/dd.c:929
 bus_probe_device+0x131/0x390 drivers/base/bus.c:514
 device_add+0x25b5/0x2df0 drivers/base/core.c:2165
 usb_set_configuration+0x309f/0x3710 drivers/usb/core/message.c:2027
 generic_probe+0xe7/0x280 drivers/usb/core/generic.c:210
 usb_probe_device+0x146/0x200 drivers/usb/core/driver.c:266
 really_probe+0x1373/0x1dc0 drivers/base/dd.c:552
 driver_probe_device+0x1ba/0x510 drivers/base/dd.c:709
 __device_attach_driver+0x5b8/0x790 drivers/base/dd.c:816
 bus_for_each_drv+0x28e/0x3b0 drivers/base/bus.c:454
 __device_attach+0x489/0x750 drivers/base/dd.c:882
 device_initial_probe+0x4a/0x60 drivers/base/dd.c:929
 bus_probe_device+0x131/0x390 drivers/base/bus.c:514
 device_add+0x25b5/0x2df0 drivers/base/core.c:2165
 usb_new_device+0x23e5/0x2fb0 drivers/usb/core/hub.c:2536
 hub_port_connect drivers/usb/core/hub.c:5098 [inline]
 hub_port_connect_change drivers/usb/core/hub.c:5213 [inline]
 port_event drivers/usb/core/hub.c:5359 [inline]
 hub_event+0x581d/0x72f0 drivers/usb/core/hub.c:5441
 process_one_work+0x1572/0x1ef0 kernel/workqueue.c:2269
 worker_thread+0x111b/0x2460 kernel/workqueue.c:2415
 kthread+0x4b5/0x4f0 kernel/kthread.c:256
 ret_from_fork+0x35/0x40 arch/x86/entry/entry_64.S:355

Local variable description: ----smsr@asix_mdio_read
Variable was created at:
 asix_mdio_read+0xa0/0x8f0 include/linux/netdevice.h:2180
 asix_mdio_bus_read+0xbc/0xe0 drivers/net/usb/ax88172a.c:31
=====================================================


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