[Bug 218598] pwait deadlocks on its own pid

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=218598

--- Comment #5 from commit-hook at FreeBSD.org ---
A commit in branch main references this bug:

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(-)

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