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Date:      Sun, 9 Jul 2023 22:41:27 +0000
From:      John F Carr <jfc@mit.edu>
To:        Current FreeBSD <freebsd-current@freebsd.org>
Subject:   shell hung in fork system call
Message-ID:  <909E2C96-3BFA-41AD-8EE7-0902231C2B95@mit.edu>

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Kernel and system at a146207d66f320ed239c1059de9df854b66b55b7 plus some irr=
elevant local changes, four 64 bit ARM processors, make.conf sets CPUTYPE?=
=3Dcortex-a57.

I typed ^C while /bin/sh was starting a pipeline and my shell got hung in t=
he middle of fork().

>From the terminal:

# git log --oneline --|more
^C^C^C
load: 3.26  cmd: sh 95505 [fork] 5308.67r 0.00u 0.03s 0% 2860k
mi_switch+0x198 sleepq_switch+0xfc sleepq_timedwait+0x40 _sleep+0x264 fork1=
+0x67c sys_fork+0x34 do_el0_sync+0x4c8 handle_el0_sync+0x44=20
load: 3.16  cmd: sh 95505 [fork] 5311.75r 0.00u 0.03s 0% 2860k
mi_switch+0x198 sleepq_switch+0xfc sleepq_timedwait+0x40 _sleep+0x264 fork1=
+0x67c sys_fork+0x34 do_el0_sync+0x4c8 handle_el0_sync+0x44=20

According to ps -d on another terminal the shell has no children:

  PID TT  STAT       TIME COMMAND
[...]
  873 u0  IWs     0:00.00 `-- login [pam] (login)
  874 u0  I       0:00.17   `-- -sh (sh)
95504 u0  I       0:00.01     `-- su -
95505 u0  D+      0:00.05       `-- -su (sh)
[...]

Nothing on the (115200 bps serial) console.  No change in system performanc=
e.

The system is busy copying a large amount of data from the network to a ZFS=
 pool on spinning disks.  The git|more pipeline could have taken some time =
to get going while I/O requests worked their way through the queue.  It wou=
ld not have touched the busy pool, only the zroot pool on an SSD.

Has anything changed recently that might cause this?





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