ipmi: Clear drvdata when interface is removed

This patch fixes a bug on hotmod removing.

After ipmi interface is removed using hotmod, kernel panic occurs when
rmmod impi_si.  For example, try this:

 # echo "remove,"`cat /proc/ipmi/0/params` > \
 /sys/module/ipmi_si/parameters/hotmod
 # rmmod ipmi_si

Then, rmmod fails with the following messages.

  ------------[ cut here ]------------
  WARNING: CPU: 12 PID: 10819 at /mnt/repos/linux/lib/list_debug.c:53 __list_del_entry+0x63/0xd0()
  CPU: 12 PID: 10819 Comm: rmmod Not tainted 3.17.0-rc1 #19
  Hardware name: FUJITSU-SV PRIMERGY BX920 S2/D3030, BIOS 080015 Rev.3D81.3030 02/10/2012
  Call Trace:
    dump_stack+0x45/0x56
    warn_slowpath_common+0x7d/0xa0
    warn_slowpath_fmt+0x4c/0x50
    __list_del_entry+0x63/0xd0
    list_del+0xd/0x30
    cleanup_one_si+0x2a/0x230 [ipmi_si]
    ipmi_pnp_remove+0x15/0x20 [ipmi_si]
    pnp_device_remove+0x24/0x40
    __device_release_driver+0x7f/0xf0
    driver_detach+0xb0/0xc0
    bus_remove_driver+0x55/0xd0
    driver_unregister+0x2c/0x50
    pnp_unregister_driver+0x12/0x20
    cleanup_ipmi_si+0xbc/0xf0 [ipmi_si]
    SyS_delete_module+0x132/0x1c0
    system_call_fastpath+0x16/0x1b
  ---[ end trace 70b4377268f85c23 ]---

list_del in cleanup_one_si() fails because the smi_info is already
removed when hotmod removing.

When ipmi interface is removed by hotmod, smi_info is removed by
cleanup_one_si(), but is is still set in drvdata.  Therefore when rmmod
ipmi_si, ipmi_pnp_remove tries to remove it again and fails.

By this patch, a pointer to smi_info in drvdata is cleared when hotmod
removing so that it will be not accessed when rmmod.

changelog:
v2:
- Clear drvdata in cleanup_one_si
- Change subject

v1:
https://lkml.org/lkml/2014/9/8/741



Signed-off-by: Takao Indoh <indou.takao@jp.fujitsu.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>