Unhandled prefetch abort when probing USB flash drive

[Joshua Scott]

Hi,

I have been running into a kernel panic when probing a USB flash drive, and was after some advice or suggestions on what might be going wrong.

First up, the details of my setup:
 * Initially seen on Linux 5.7.19, but I've tested on a vanilla copy of Linux 5.15.0 without any extra modules, and the panic still occurs.
 * Flash drive (lsusb): Bus 001 Device 002: ID 1005:b113 Apacer Technology, Inc. Handy Steno 2.0/HT203
 * Our system is based on the Marvell 98DX323x SoC (Arm v7, based on the Armada 370/XP)

The panic occurs after sd_probe() gets called, with the USB flash drive attached. This occurs around 1 time out of 100. We first saw this during a reboot, but it can be reproduced much faster by loading and unloading the sd_mod module in a loop, to exercise the probe function.

When adding some diagnostic print statements, I found that adding a delay into sd_probe(), just after the call to device_add_disk(), seems to prevent the issue.

The actual headline of the panic is not always the same, we have seen:
* Unhandled fault: external abort on non-linefetch (0x808) at 0x9fbfa73c
* Unhandled fault: imprecise external abort (0x1416) at 0x76f5e508
* Unhandled prefetch abort: external abort on non-linefetch (0x1008) at 0x803c8a88

Included below is an example of the panic output.

Thank you,
Joshua Scott

Unhandled prefetch abort: external abort on non-linefetch (0x1008) at 0x8018fe20
Internal error: : 1008 [#1] PREEMPT SMP ARM
Modules linked in: sd_mod(+) diag tipc platform_driver(O) ipifwd(PO) usb_storage scsi_mod [last unloaded: sd_mod]
CPU: 0 PID: 178 Comm: udevd Tainted: P           O      5.7.19-at1 #39
Hardware name: Marvell Armada 370/XP (Device Tree)
PC is at sys_clock_gettime32+0x58/0xc4
LR is at ret_fast_syscall+0x0/0x54
pc : [<8018fe20>]    lr : [<80100060>]    psr: a00e0013
sp : 9dfcdf80  ip : 10c5387d  fp : 00041150
r10: 00000107  r9 : 9dfcc000  r8 : 80100288
r7 : 00000107  r6 : 00000000  r5 : 7eddb208  r4 : 80c052c8
r3 : 8018ea90  r2 : 00000001  r1 : 7eddb208  r0 : 00000001
Flags: NzCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
Control: 10c5387d  Table: 1dfc006a  DAC: 00000051
Process udevd (pid: 178, stack limit = 0xfbd1de7a)
Stack: (0x9dfcdf80 to 0x9dfce000)
df80: 00000000 00000000 00000000 ed40bc3c 000000fc ed40bc3c 00000008 00000001
dfa0: 7eddb208 80100060 00000001 7eddb208 00000001 7eddb208 eec19c0e eec19c0e
dfc0: 00000001 7eddb208 00000000 00000107 000402c4 00040308 7eddbcd0 00041150
dfe0: 76f38060 7eddb1f0 0002505c 76ed9bc4 600e0010 00000001 00000000 00000000
[<8018fe20>] (sys_clock_gettime32) from [<80100060>] (ret_fast_syscall+0x0/0x54)
Exception stack(0x9dfcdfa8 to 0x9dfcdff0)
dfa0:                   00000001 7eddb208 00000001 7eddb208 eec19c0e eec19c0e
dfc0: 00000001 7eddb208 00000000 00000107 000402c4 00040308 7eddbcd0 00041150
dfe0: 76f38060 7eddb1f0 0002505c 76ed9bc4
Code: e5933080 e3530000 0a000018 e5933008 (e1a0100d) 
---[ end trace 98c4e7c1cd29d9e3 ]---