Re: [HMM 12/15] mm/migrate: new memory migration helper for use with device memory v4

From: Evgeny Baskakov
Date: Mon Jul 10 2017 - 18:59:44 EST

On 6/30/17 5:57 PM, Jerome Glisse wrote:

Hi Jerome,

I am seeing a strange crash in our code that uses the hmm_device_new() helper. After the driver is repeatedly loaded/unloaded, hmm_device_new() suddenly returns NULL.

I have reproduced this with the dummy driver from the hmm-next branch:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000208

(gdb) bt
#0 hmm_devmem_add (ops=0xffffffffa003a140, device=0x0 <irq_stack_union>, size=0x4000000) at mm/hmm.c:997
#1 0xffffffffa0038236 in dmirror_probe (pdev=<optimized out>) at drivers/char/hmm_dmirror.c:1106
#2 0xffffffff815acfcb in platform_drv_probe (_dev=0xffff88081368ca78) at drivers/base/platform.c:578
#3 0xffffffff815ab0a4 in really_probe (drv=<optimized out>, dev=<optimized out>) at drivers/base/dd.c:385
#4 driver_probe_device (drv=0xffffffffa003b028, dev=0xffff88081368ca78) at drivers/base/dd.c:529
#5 0xffffffff815ab1d4 in __driver_attach (dev=0xffff88081368ca78, data=0xffffffffa003b028) at drivers/base/dd.c:763
#6 0xffffffff815a911d in bus_for_each_dev (bus=<optimized out>, start=<optimized out>, data=0x4000000, fn=0x18 <irq_stack_union+24>) at drivers/base/bus.c:313
#7 0xffffffff815aa98e in driver_attach (drv=<optimized out>) at drivers/base/dd.c:782
#8 0xffffffff815aa585 in bus_add_driver (drv=0xffffffffa003b028) at drivers/base/bus.c:669
#9 0xffffffff815abc10 in driver_register (drv=0xffffffffa003b028) at drivers/base/driver.c:168
#10 0xffffffff815acf46 in __platform_driver_register (drv=<optimized out>, owner=<optimized out>) at drivers/base/platform.c:636

Can you please look into this?

Here's a command to reproduce, using the script (taken from a sanity suite you provided earlier, attached):

$ while true; do sudo ./; done


Evgeny Baskakov

Description: Bourne shell script