Date: Mon, 10 Jul 2023 02:59:35 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: John F Carr <jfc@mit.edu> Cc: Current FreeBSD <freebsd-current@freebsd.org> Subject: Re: shell hung in fork system call Message-ID: <ZKtJ51ZHZWCixlk9@kib.kiev.ua> In-Reply-To: <52A8F775-17D9-4240-A444-98AD5339622F@mit.edu> References: <909E2C96-3BFA-41AD-8EE7-0902231C2B95@mit.edu> <ZKtB8B_Fs0GwVCcP@kib.kiev.ua> <52A8F775-17D9-4240-A444-98AD5339622F@mit.edu>
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On Sun, Jul 09, 2023 at 11:36:03PM +0000, John F Carr wrote:
>
>
> > On Jul 9, 2023, at 19:25, Konstantin Belousov <kostikbel@gmail.com> wrote:
> >
> > On Sun, Jul 09, 2023 at 10:41:27PM +0000, John F Carr wrote:
> >> Kernel and system at a146207d66f320ed239c1059de9df854b66b55b7 plus some irrelevant local changes, four 64 bit ARM processors, make.conf sets CPUTYPE?=cortex-a57.
> >>
> >> I typed ^C while /bin/sh was starting a pipeline and my shell got hung in the 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
> >> 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
> >>
> >> 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 performance.
> >>
> >> 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 would not have touched the busy pool, only the zroot pool on an SSD.
> >>
> >> Has anything changed recently that might cause this?
> >
> > There was some change around fork, but your sleep seems to be not from
> > that change. Can you show the wait channel for the process? Do something
> > like
> > $ ps alxww
> >
>
> UID PID PPID C PRI NI VSZ RSS MWCHAN STAT TT TIME COMMAND
> 0 95505 95504 2 20 0 13508 2876 fork D+ u0 0:00.13 -su (sh)
>
> This is probably the same information displayed as [fork] in the output from ^T.
>
> Does it correspond to the source line
>
> pause("fork", hz / 2);
>
> ?
Yes, it is rate-limiting code. Still it is interesting to see the whole
ps output.
Do you have 7a70f17ac4bd64dc1a5020f in your source?
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