[Bug 230808] rand_harvestq high CPU utilization

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=230808

            Bug ID: 230808
           Summary: rand_harvestq high CPU utilization
           Product: Base System
           Version: CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: kern
          Assignee: bugs at FreeBSD.org
          Reporter: danilo at FreeBSD.org

I'm seeing a high CPU utilization by the thread rand_harvestq.

It's easily reproducible in my system, just reading from /dev/urandom for 2
seconds is enough to trigger this issue. The rand_harvestq start eating CPU for
minutes and the system (at least the graphical interface) start freezing for
few seconds.

After some minutes the thread stop the high CPU consumption and the system stop
freezing.

 PID USERNAME    PRI NICE   SIZE    RES STATE    C   TIME    WCPU COMMAND
   19 root       -16    -      0    16K CPU3     3   6:31 100.00% rand_harvestq
   11 root       155 ki31      0    64K CPU2     2 327:17  98.30% idle{idle:
cpu2}
   11 root       155 ki31      0    64K RUN      3 323:58  69.61% idle{idle:
cpu3}
   11 root       155 ki31      0    64K CPU0     0 325:32  69.01% idle{idle:
cpu0}
   11 root       155 ki31      0    64K RUN      1 327:07  58.61% idle{idle:
cpu1}

 PID USERNAME    PRI NICE   SIZE    RES STATE    C   TIME    WCPU COMMAND
   19 root       -16    -      0    16K CPU1     1  27:50  99.98% rand_harvestq
   11 root       155 ki31      0    64K CPU2     2 359:58  98.65% idle{idle:
cpu2}
   11 root       155 ki31      0    64K RUN      3 351:16  98.41% idle{idle:
cpu3}
   11 root       155 ki31      0    64K CPU0     0 357:59  94.45% idle{idle:
cpu0}
   11 root       155 ki31      0    64K RUN      1 345:23   4.51% idle{idle:
cpu1}


  PID USERNAME    PRI NICE   SIZE    RES STATE    C   TIME    WCPU COMMAND
   19 root       -16    -      0    16K CPU3     3  28:16 100.00% rand_harvestq
   11 root       155 ki31      0    64K CPU0     0 358:24  97.82% idle{idle:
cpu0}
   11 root       155 ki31      0    64K RUN      2 360:23  97.78% idle{idle:
cpu2}
   11 root       155 ki31      0    64K RUN      3 351:36  70.94% idle{idle:
cpu3}
   11 root       155 ki31      0    64K CPU1     1 345:31  25.92% idle{idle:
cpu1}


More information about my setup

$ uname -a
FreeBSD capeta 12.0-ALPHA2 FreeBSD 12.0-ALPHA2 #14 r337973M: Fri Aug 17
13:03:01 -03 2018    
danilo at capeta:/usr/obj/usr/src/amd64.amd64/sys/GENERIC-NODEBUG  amd64

$ sysctl kern.random
kern.random.fortuna.minpoolsize: 64
kern.random.harvest.mask_symbolic:
PURE_RDRAND,[UMA],[FS_ATIME],SWI,INTERRUPT,NET_NG,NET_ETHER,NET_TUN,MOUSE,KEYBOARD,ATTACH,CACHED
kern.random.harvest.mask_bin: 00000010000000111111111
kern.random.harvest.mask: 66047
kern.random.random_sources: 'Intel Secure Key RNG'

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