statically initialize struct pid for swapper

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.

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Herbert Poetzl <herbert@13thfloor.at>
Cc: <containers@lists.osdl.org>
Acked-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 31 insertions, 0 deletions

diff --git a/include/linux/init_task.h b/include/linux/init_task.h
index 45170b2fa253..a68835fc8c04 100644
--- a/include/linux/init_task.h
+++ b/include/linux/init_task.h
@@ -88,6 +88,28 @@ extern struct nsproxy init_nsproxy;
 
 extern struct group_info init_groups;
 
+#define INIT_STRUCT_PID {                                               \
+        .count          = ATOMIC_INIT(1),                               \
+        .nr             = 0,                                            \
+        /* Don't put this struct pid in pid_hash */                     \
+        .pid_chain      = { .next = NULL, .pprev = NULL },              \
+        .tasks          = {                                             \
+                { .first = &init_task.pids[PIDTYPE_PID].node },         \
+                { .first = &init_task.pids[PIDTYPE_PGID].node },        \
+                { .first = &init_task.pids[PIDTYPE_SID].node },         \
+        },                                                              \
+        .rcu            = RCU_HEAD_INIT,                                \
+}
+
+#define INIT_PID_LINK(type)                                     \
+{                                                               \
+        .node = {                                               \
+                .next = NULL,                                   \
+                .pprev = &init_struct_pid.tasks[type].first,    \
+        },                                                      \
+        .pid = &init_struct_pid,                                \
+}
+
 /*
  *  INIT_TASK is used to set up the first task table, touch at
  * your own risk!. Base=0, limit=0x1fffff (=2MB)
@@ -139,6 +161,11 @@ extern struct group_info init_groups;
         .cpu_timers     = INIT_CPU_TIMERS(tsk.cpu_timers),              \
         .fs_excl        = ATOMIC_INIT(0),                               \
         .pi_lock        = __SPIN_LOCK_UNLOCKED(tsk.pi_lock),            \
+        .pids = {                                                       \
+                [PIDTYPE_PID]  = INIT_PID_LINK(PIDTYPE_PID),            \
+                [PIDTYPE_PGID] = INIT_PID_LINK(PIDTYPE_PGID),           \
+                [PIDTYPE_SID]  = INIT_PID_LINK(PIDTYPE_SID),            \
+        },                                                              \
         INIT_TRACE_IRQFLAGS                                             \
         INIT_LOCKDEP                                                    \
 }
diff --git a/include/linux/pid.h b/include/linux/pid.h
index 33d343880d89..1e0e4e3423a6 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -51,6 +51,8 @@ struct pid
         struct rcu_head rcu;
 };
 
+extern struct pid init_struct_pid;
+
 struct pid_link
 {
         struct hlist_node node;
diff --git a/kernel/pid.c b/kernel/pid.c
index d76f59326bd4..eb66bd2953ab 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -27,11 +27,13 @@
 #include <linux/bootmem.h>
 #include <linux/hash.h>
 #include <linux/pid_namespace.h>
+#include <linux/init_task.h>
 
 #define pid_hashfn(nr) hash_long((unsigned long)nr, pidhash_shift)
 static struct hlist_head *pid_hash;
 static int pidhash_shift;
 static struct kmem_cache *pid_cachep;
+struct pid init_struct_pid = INIT_STRUCT_PID;
 
 int pid_max = PID_MAX_DEFAULT;