Commit c7c64641 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
Browse files

[PATCH] pidhash: don't use zero pids

daemonize() calls set_special_pids(1,1), while init and kernel threads spawned
from init/main.c:init() run with 0,0 special pids.  This patch changes
INIT_SIGNALS() so that that they run with ->pgrp == ->session == 1 also.  This
patch relies on fact that swapper's pid == 1.

Now we have no hashed zero pids in pid_hash[].

User-space visibible change is that now /sbin/init runs with (1,1) special
pids and becomes a session leader.

Quoting Eric W. Biederman:
> daemonize consuming pids (1,1) then consumes pgrp 1.  So that when
> /sbin/init calls setsid() it thinks /sbin/init is a process group
> leader and setsid() fails.  So /sbin/init wants pgrp 1 session 1
> but doesn't get it.  I am pretty certain daemonize did not exist so
> /sbin/init got pgrp 1 session 1 in 2.4.
> That is the bug that is being fixed.
> This patch takes things one step farther and essentially calls
> setsid() for pid == 1 before init is execed.  That is new behavior
> but it cleans up the kernel as we now do not need to support the
> case of a process without a process group or a session.
> The only process that could have possibly cared was /sbin/init
> and it already calls setsid() because it doesn't want that.
> If this was going to break anything noticeable the change in behavior
> from 2.4 to 2.6 would have already done that.

Signed-off-by: default avatarOleg Nesterov <>
Cc: "Eric W. Biederman" <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 73b9ebfe
......@@ -62,6 +62,8 @@
.posix_timers = LIST_HEAD_INIT(sig.posix_timers), \
.cpu_timers = INIT_CPU_TIMERS(sig.cpu_timers), \
.rlim = INIT_RLIMITS, \
.pgrp = 1, \
.session = 1, \
#define INIT_SIGHAND(sighand) { \
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