git: 5bdce6ff546e - main - Remove deadlock in rc caused by pwait waiting for itself.

[Kyle Evans]

On Thu, Jan 21, 2021 at 3:36 PM Alexander V. Chernikov
<melifaro at freebsd.org> wrote:
>
> The branch main has been updated by melifaro:
>
> URL: https://cgit.FreeBSD.org/src/commit/?id=5bdce6ff546e00673f9f515d2165d02901e858aa
>
> commit 5bdce6ff546e00673f9f515d2165d02901e858aa
> Author:     Alexander V. Chernikov <melifaro at FreeBSD.org>
> AuthorDate: 2021-01-21 21:26:15 +0000
> Commit:     Alexander V. Chernikov <melifaro at FreeBSD.org>
> CommitDate: 2021-01-21 21:36:37 +0000
>
>     Remove deadlock in rc caused by pwait waiting for itself.
>
>     The following situation can trigger the deadlock:
>     1) Long time ago a_service was started through rc.d
>     2) We want to restart a_service and issue service a_service restart
>     3) rc.subr reads current process PID (via file or process),
>        sends TERM signal and runs pwait with PID harvested
>     4) a_service process dies very quickly so it's PID becomes available.
>        It is possible that while original process was running,
>        PID counter overflowed and pwait got assigned a_service's PID.
>
>     This patch ignores pid(s) to wait that are equal to pwait PID.
>
>     Reported by:    Dan McGregor, Boris Lytochkin
>     Submitted by:   Boris Lytochkin <lytboris at gmail.com>
>     Reviewed By:    0mp
>     MFC after:      2 weeks
>     PR:             218598
>     Differential Revision: https://reviews.freebsd.org/D28240
> ---
>  bin/pwait/pwait.1 | 6 +++++-
>  bin/pwait/pwait.c | 4 ++++
>  2 files changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/bin/pwait/pwait.1 b/bin/pwait/pwait.1
> index 0452203eb4a1..b9b651bfc905 100644
> --- a/bin/pwait/pwait.1
> +++ b/bin/pwait/pwait.1
> @@ -32,7 +32,7 @@
>  .\"
>  .\" $FreeBSD$
>  .\"
> -.Dd October 5, 2020
> +.Dd January 21, 2021
>  .Dt PWAIT 1
>  .Os
>  .Sh NAME
> @@ -145,6 +145,10 @@ is not a substitute for the
>  .Xr wait 1
>  builtin
>  as it will not clean up any zombies or state in the parent process.
> +.Pp
> +To avoid deadlock,
> +.Nm
> +will ignore its own pid, if it is provided as a process id to wait for.
>  .Sh HISTORY
>  A
>  .Nm
> diff --git a/bin/pwait/pwait.c b/bin/pwait/pwait.c
> index f39922b48eb9..85cc6b994acf 100644
> --- a/bin/pwait/pwait.c
> +++ b/bin/pwait/pwait.c
> @@ -146,6 +146,10 @@ main(int argc, char *argv[])
>                         warnx("%s: bad process id", s);
>                         continue;
>                 }
> +               if (pid == getpid()) {
> +                       warnx("%s: skiping my own pid", s);
> +                       continue;
> +               }

nit: "skipping"