pids: init_struct_pid.tasks should never see the swapper process
"statically initialize struct pid for swapper" commit 820e45db says:
Statically initialize a struct pid for the swapper process (pid_t == 0)
and attach it to init_task. This is needed so task_pid(), task_pgrp()
and task_session() interfaces work on the swapper process also.
OK, but:
- it doesn't make sense to add init_task.pids[].node into
init_struct_pid.tasks[], and in fact this just wrong.
idle threads are special, they shouldn't be visible on any
global list. In particular do_each_pid_task(init_struct_pid)
shouldn't see swapper.
This is the actual reason why kill(0, SIGKILL) from /sbin/init
(which starts with 0,0 special pids) crashes the kernel. The
signal sent to pgid/sid == 0 must never see idle threads, even
if the previous patch fixed the crash itself.
- we have other idle threads running on the non-boot CPUs, see
the next patch.
Change INIT_STRUCT_PID/INIT_PID_LINK to create the empty/unhashed
hlist_head/hlist_node. Like any other idle thread swapper can never exit,
so detach_pid()->__hlist_del() is not possible, but we could change
INIT_PID_LINK() to set pprev = &next if needed.
All we need is the valid swapper->pids[].pid == &init_struct_pid.
Reported-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>
Cc: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 6deb1ba..94fecb7 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -45,9 +45,9 @@
#define INIT_STRUCT_PID { \
.count = ATOMIC_INIT(1), \
.tasks = { \
- { .first = &init_task.pids[PIDTYPE_PID].node }, \
- { .first = &init_task.pids[PIDTYPE_PGID].node }, \
- { .first = &init_task.pids[PIDTYPE_SID].node }, \
+ { .first = NULL }, \
+ { .first = NULL }, \
+ { .first = NULL }, \
}, \
.level = 0, \
.numbers = { { \
@@ -61,7 +61,7 @@
{ \
.node = { \
.next = NULL, \
- .pprev = &init_struct_pid.tasks[type].first, \
+ .pprev = NULL, \
}, \
.pid = &init_struct_pid, \
}