[Bug 253608] hostapd 100% CPU usage after WiFi device disappears

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=253608

            Bug ID: 253608
           Summary: hostapd 100% CPU usage after WiFi device disappears
           Product: Base System
           Version: 12.2-STABLE
          Hardware: arm64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: wireless
          Assignee: wireless at FreeBSD.org
          Reporter: damjan.jov at gmail.com

Some other bug causes my USB bus to sporadically undergo some kind of reset,
making all USB devices appear to disconnect and then reconnect.

One of my USB devices is a WiFi dongle, which hostapd is running with. When it
disconnects, hostapd CPU usage jumps to 100%, and stays there until manually
killed:

# truss -s 1024 -f -p 34705
34705: read(5,0x80121f2c0,524288)                ERR#6 'Device not configured'
34705: select(7,{ 4 5 6 },{ },{ },{ 2.635212 })  = 1 (0x1)
34705: read(5,0x80121f2c0,524288)                ERR#6 'Device not configured'
34705: select(7,{ 4 5 6 },{ },{ },{ 2.635171 })  = 1 (0x1)
34705: read(5,0x80121f2c0,524288)                ERR#6 'Device not configured'
34705: select(7,{ 4 5 6 },{ },{ },{ 2.635120 })  = 1 (0x1)
34705: read(5,0x80121f2c0,524288)                ERR#6 'Device not configured'
34705: select(7,{ 4 5 6 },{ },{ },{ 2.635069 })  = 1 (0x1)
34705: read(5,0x80121f2c0,524288)                ERR#6 'Device not configured'
34705: select(7,{ 4 5 6 },{ },{ },{ 2.635001 })  = 1 (0x1)

# lsof -n |grep hostapd
hostapd   34705       root  cwd     VDIR 2669942718,3349274250                
36       4 /
hostapd   34705       root  rtd     VDIR 2669942718,3349274250                
36       4 /
hostapd   34705       root    0u    VCHR                  0,16               
0t0      16 /dev/null
hostapd   34705       root    1u    VCHR                  0,16               
0t0      16 /dev/null
hostapd   34705       root    2u    VCHR                  0,16               
0t0      16 /dev/null
hostapd   34705       root    3u    IPv4    0xfffff80016a2b040               
0t0     UDP *:*
hostapd   34705       root    4u     rte    0xfffff8001334b1e0               
0t0         
hostapd   34705       root    5u    VCHR                  0,40               
0t0      40 /dev/bpf
hostapd   34705       root    6u    unix    0xfffff8011139e000               
0t0         /var/run/hostapd/wlan0
hostapd   34705       root    7r    VDIR 2669942718,3349274250                
43     712 /var/run
hostapd   34705       root    8w    VREG 2669942718,3349274250                 
5  262304 /var/run/hostapd.pid


I consider this a hostapd bug, because the WiFi dongle could also get unplugged
manually to reproduce it.

When a WiFi device disappears, hostapd should do something better than get
stuck in an infinite loop.

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