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Re: [PATCH] udevProcessCSS: fix segfault



On 9/22/20 8:26 AM, Erik Skultety wrote:
On Mon, Sep 21, 2020 at 07:06:32PM +0200, Marc Hartmayer wrote:
Don't process subchannel devices where `def->driver` is not set. This
fixes the following segfault:

Thread 21 "nodedev-init" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x3ffb08fc910 (LWP 64303)]
(gdb) bt
  #0  0x000003fffd1272b4 in __strcmp_vx () at /lib64/libc.so.6
  #1  0x000003ffc260c3a8 in udevProcessCSS (device=0x3ff9018d130, def=0x3ff90194a90)
  #2  0x000003ffc260cb78 in udevGetDeviceDetails (device=0x3ff9018d130, def=0x3ff90194a90)
  #3  0x000003ffc260d126 in udevAddOneDevice (device=0x3ff9018d130)
  #4  0x000003ffc260d414 in udevProcessDeviceListEntry (udev=0x3ffa810d800, list_entry=0x3ff90001990)
  #5  0x000003ffc260d638 in udevEnumerateDevices (udev=0x3ffa810d800)
  #6  0x000003ffc260e08e in nodeStateInitializeEnumerate (opaque=0x3ffa810d800)
  #7  0x000003fffdaa14b6 in virThreadHelper (data=0x3ffa810df00)
  #8  0x000003fffc309ed6 in start_thread ()
  #9  0x000003fffd185e66 in thread_start ()
(gdb) p *def
$2 = {
   name = 0x0,
   sysfs_path = 0x3ff90198e80 "/sys/devices/css0/0.0.ff40",

Okay, this patch fixes the segfault. However, if ^this generated it because the
driver name is not set, how do we even get to the resulting device tree as
outlined in 05e6cdafa6e0?

+- css_0_0_003a
     |
     +- ccw_0_0_1a2b
         |
         +- scsi_host0

What kind of CSS device is the one causing the error? If we skip this CSS
device, we don't generate a name for it and don't put it in the list, so I'm
quite puzzled on what I missed in the IBM document and thus in the review
process.

FWIW:
Reviewed-by: Erik Skultety <eskultet redhat com>


Erik,
for whatever reason Marcs system does not have the subchannel device driver "chsc_subchannel" loaded. Therefore the subchannel is not bound to any driver and by the way this would be a filtered device since we want to show the users only io_subchannel and vfio_ccw subchannels.
The tree above shows a subchannel bound to the io_subchannel device driver.
Maybe it helps you to see a full example of how it looks on my system:

# virsh nodedev-list --tree
computer
  |
  +- css_0_0_000e
  |   |
  |   +- ccw_0_0_f500
  |
  +- css_0_0_000f
  |   |
  |   +- ccw_0_0_f501
  |
  +- css_0_0_0010
  |   |
  |   +- ccw_0_0_f502
  |
  +- css_0_0_0011
  |   |
  |   +- ccw_0_0_bd00
  |
  +- css_0_0_0012
  |   |
  |   +- ccw_0_0_bd01
  |
  +- css_0_0_0013
  |   |
  |   +- ccw_0_0_bd02
  |
  +- css_0_0_002f
  |   |
  |   +- ccw_0_0_19c0
  |       |
  |       +- scsi_host3
  |           |
  |           +- scsi_target3_0_1
  |               |
  |               +- scsi_3_0_1_1078935649
  |                   |
  |                   +- block_sda_36005076307ffc5e3000000000000614f
  |                   +- scsi_generic_sg0
  |
  +- css_0_0_0038
  |   |
  |   +- ccw_0_0_1900
  |       |
  |       +- scsi_host1
  |           |
  |           +- scsi_target1_0_0
  |           |   |
  |           |   +- scsi_1_0_0_1075986530
  |           |   |   |
  |           |   |   +- block_sdd_36005076307ffc5e30000000000006222
  |           |   |   +- scsi_generic_sg3
  |           |   |
  |           |   +- scsi_1_0_0_1078935649
  |           |       |
  |           |       +- block_sdc_36005076307ffc5e3000000000000614f
  |           |       +- scsi_generic_sg2
  |           |
  |           +- scsi_target1_0_2
  |               |
  |               +- scsi_1_0_2_1075986530
  |               |   |
  |               |   +- block_sdf_36005076307ffc5e30000000000006222
  |               |   +- scsi_generic_sg5
  |               |
  |               +- scsi_1_0_2_1078935649
  |                   |
  |                   +- block_sde_36005076307ffc5e3000000000000614f
  |                   +- scsi_generic_sg4
  |
  +- css_0_0_003a
  |   |
  |   +- ccw_0_0_1940
  |       |
  |       +- scsi_host0
  |           |
  |           +- scsi_target0_0_1
  |           |   |
  |           |   +- scsi_0_0_1_1075986530
  |           |   |   |
  |           |   |   +- block_sdi_36005076307ffc5e30000000000006222
  |           |   |   +- scsi_generic_sg8
  |           |   |
  |           |   +- scsi_0_0_1_1078935649
  |           |       |
  |           |       +- block_sdh_36005076307ffc5e3000000000000614f
  |           |       +- scsi_generic_sg7
  |           |
  |           +- scsi_target0_0_3
  |               |
  |               +- scsi_0_0_3_1075986530
  |               |   |
  |               |   +- block_sdg_36005076307ffc5e30000000000006222
  |               |   +- scsi_generic_sg6
  |               |
  |               +- scsi_0_0_3_1078935649
  |                   |
  |                   +- block_sdb_36005076307ffc5e3000000000000614f
  |                   +- scsi_generic_sg1
  |
  +- css_0_0_003c
  |   |
  |   +- ccw_0_0_1980
  |       |
  |       +- scsi_host2
  |
  +- css_0_0_006b
  |   |
  |   +- ccw_0_0_1000
  |       |
  |       +- block_dasdg_IBM_750000000DHVL1_0001_00
  |
  +- css_0_0_006c
  |   |
  |   +- ccw_0_0_1001
  |       |
  |       +- block_dasda_IBM_750000000DHVL1_0001_01
  |
  +- css_0_0_006d
  |   |
  |   +- ccw_0_0_1002
  |       |
  |       +- block_dasdb_IBM_750000000DHVL1_0001_02
  |
  +- css_0_0_006e
  |   |
  |   +- ccw_0_0_1003
  |       |
  |       +- block_dasdc_IBM_750000000DHVL1_0001_03
  |
  +- css_0_0_006f
  |   |
  |   +- ccw_0_0_1004
  |       |
  |       +- block_dasdd_IBM_750000000DHVL1_0001_04
  |
  +- css_0_0_0070
  |   |
  |   +- ccw_0_0_1005
  |       |
  |       +- block_dasdh_IBM_750000000DHVL1_0001_05
  |
  +- css_0_0_0071
  |   |
  |   +- ccw_0_0_1006
  |       |
  |       +- block_dasdf_IBM_750000000DHVL1_0001_06
  |
  +- css_0_0_0072
  |   |
  |   +- mdev_2e7237a7_0445_407e_b880_96f63a3cd17d
  |
  +- net_encbd00_02_ff_e3_80_c4_ef
  +- net_encf500_02_ff_e3_80_76_89
  +- net_lo_00_00_00_00_00_00
  +- pci_0001_00_00_0
      |
      +- net_enP1s8_82_01_2d_0c_bb_b0
      +- net_enP1s8d1_82_01_2d_0c_bb_b1

All subchannels but css_0_0_0072 are bound to io_subchannel.
css_0_0_0072 is bound to vfio-ccw and therefore lists an mdev as child.

Here are the xml dumps:
# virsh nodedev-dumpxml css_0_0_0071
<device>
  <name>css_0_0_0071</name>
  <path>/sys/devices/css0/0.0.0071</path>
  <parent>computer</parent>
  <driver>
    <name>io_subchannel</name>
  </driver>
  <capability type='css'>
    <cssid>0x0</cssid>
    <ssid>0x0</ssid>
    <devno>0x0071</devno>
  </capability>
</device>

# virsh nodedev-dumpxml css_0_0_0072
<device>
  <name>css_0_0_0072</name>
  <path>/sys/devices/css0/0.0.0072</path>
  <parent>computer</parent>
  <driver>
    <name>vfio_ccw</name>
  </driver>
  <capability type='css'>
    <cssid>0x0</cssid>
    <ssid>0x0</ssid>
    <devno>0x0072</devno>
  </capability>
</device>

I hope that helps a bit...
--
Mit freundlichen Grüßen/Kind regards
   Boris Fiuczynski

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