INIT_TASK() should initialize ->thread_group list

The trivial /sbin/init doing

	int main(void)
	{
		kill(0, SIGKILL)
	}

crashes the kernel.

This happens because __kill_pgrp_info(init_struct_pid) also sends SIGKILL
to the swapper process which runs with the uninitialized ->thread_group.

Change INIT_TASK() to initialize ->thread_group properly.

Note: the real problem is that the swapper process must not be visible to
signals, see the next patch. But this change is right anyway and fixes
the crash.

Reported-and-tested-by: Mathias Krause <mathias.krause@secunet.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: Mathias Krause <Mathias.Krause@secunet.com>
Acked-by: Roland McGrath <roland@redhat.com>
Acked-by: Serge Hallyn <serue@us.ibm.com>
Acked-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 0551e0dcb71b..6deb1ba52fdb 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -163,6 +163,7 @@ extern struct cred init_cred;
                 [PIDTYPE_PGID] = INIT_PID_LINK(PIDTYPE_PGID),           \
                 [PIDTYPE_SID]  = INIT_PID_LINK(PIDTYPE_SID),            \
         },                                                              \
+        .thread_group   = LIST_HEAD_INIT(tsk.thread_group),             \
         .dirties = INIT_PROP_LOCAL_SINGLE(dirties),                     \
         INIT_IDS                                                        \
         INIT_PERF_EVENTS(tsk)                                           \