From: Sukadev Bhattiprolu With multiple pid namespaces, a process is known by some pid_t in every ancestor pid namespace. Every time the process forks, the child process also gets a pid_t in every ancestor pid namespace. While a process is visible in >=1 pid namespaces, it can see pid_t's in only one pid namespace. We call this pid namespace it's "active pid namespace", and it is always the youngest pid namespace in which the process is known. This patch defines and uses a wrapper to find the active pid namespace of a process. The implementation of the wrapper will be changed in when support for multiple pid namespaces are added. Changelog: 2.6.22-rc4-mm2-pidns1: - [Pavel Emelianov, Alexey Dobriyan] Back out the change to use task_active_pid_ns() in child_reaper() since task->nsproxy can be NULL during task exit (so child_reaper() continues to use init_pid_ns). to implement child_reaper() since init_pid_ns.child_reaper to implement child_reaper() since tsk->nsproxy can be NULL during exit. 2.6.21-rc6-mm1: - Rename task_pid_ns() to task_active_pid_ns() to reflect that a process can have multiple pid namespaces. Signed-off-by: Sukadev Bhattiprolu Acked-by: Pavel Emelianov Cc: Eric W. Biederman Cc: Cedric Le Goater Cc: Dave Hansen Cc: Serge Hallyn Cc: Herbert Poetzel Cc: Kirill Korotaev Signed-off-by: Andrew Morton --- fs/exec.c | 2 +- fs/proc/proc_misc.c | 3 ++- include/linux/pid_namespace.h | 5 +++++ kernel/exit.c | 5 +++-- kernel/nsproxy.c | 2 +- kernel/pid.c | 4 ++-- 6 files changed, 14 insertions(+), 7 deletions(-) diff -puN fs/exec.c~pid-namespaces-define-and-use-task_active_pid_ns-wrapper fs/exec.c --- a/fs/exec.c~pid-namespaces-define-and-use-task_active_pid_ns-wrapper +++ a/fs/exec.c @@ -804,7 +804,7 @@ static int de_thread(struct task_struct * so it is safe to do it under read_lock. */ if (unlikely(tsk->group_leader == child_reaper(tsk))) - tsk->nsproxy->pid_ns->child_reaper = tsk; + task_active_pid_ns(tsk)->child_reaper = tsk; zap_other_threads(tsk); read_unlock(&tasklist_lock); diff -puN fs/proc/proc_misc.c~pid-namespaces-define-and-use-task_active_pid_ns-wrapper fs/proc/proc_misc.c --- a/fs/proc/proc_misc.c~pid-namespaces-define-and-use-task_active_pid_ns-wrapper +++ a/fs/proc/proc_misc.c @@ -94,7 +94,8 @@ static int loadavg_read_proc(char *page, LOAD_INT(a), LOAD_FRAC(a), LOAD_INT(b), LOAD_FRAC(b), LOAD_INT(c), LOAD_FRAC(c), - nr_running(), nr_threads, current->nsproxy->pid_ns->last_pid); + nr_running(), nr_threads, + task_active_pid_ns(current)->last_pid); return proc_calc_metrics(page, start, off, count, eof, len); } diff -puN include/linux/pid_namespace.h~pid-namespaces-define-and-use-task_active_pid_ns-wrapper include/linux/pid_namespace.h --- a/include/linux/pid_namespace.h~pid-namespaces-define-and-use-task_active_pid_ns-wrapper +++ a/include/linux/pid_namespace.h @@ -39,6 +39,11 @@ static inline void put_pid_ns(struct pid kref_put(&ns->kref, free_pid_ns); } +static inline struct pid_namespace *task_active_pid_ns(struct task_struct *tsk) +{ + return tsk->nsproxy->pid_ns; +} + static inline struct task_struct *child_reaper(struct task_struct *tsk) { return init_pid_ns.child_reaper; diff -puN kernel/exit.c~pid-namespaces-define-and-use-task_active_pid_ns-wrapper kernel/exit.c --- a/kernel/exit.c~pid-namespaces-define-and-use-task_active_pid_ns-wrapper +++ a/kernel/exit.c @@ -908,8 +908,9 @@ fastcall NORET_TYPE void do_exit(long co if (unlikely(!tsk->pid)) panic("Attempted to kill the idle task!"); if (unlikely(tsk == child_reaper(tsk))) { - if (tsk->nsproxy->pid_ns != &init_pid_ns) - tsk->nsproxy->pid_ns->child_reaper = init_pid_ns.child_reaper; + if (task_active_pid_ns(tsk) != &init_pid_ns) + task_active_pid_ns(tsk)->child_reaper = + init_pid_ns.child_reaper; else panic("Attempted to kill init!"); } diff -puN kernel/nsproxy.c~pid-namespaces-define-and-use-task_active_pid_ns-wrapper kernel/nsproxy.c --- a/kernel/nsproxy.c~pid-namespaces-define-and-use-task_active_pid_ns-wrapper +++ a/kernel/nsproxy.c @@ -86,7 +86,7 @@ static struct nsproxy *create_new_namesp goto out_ipc; } - new_nsp->pid_ns = copy_pid_ns(flags, tsk->nsproxy->pid_ns); + new_nsp->pid_ns = copy_pid_ns(flags, task_active_pid_ns(tsk)); if (IS_ERR(new_nsp->pid_ns)) { err = PTR_ERR(new_nsp->pid_ns); goto out_pid; diff -puN kernel/pid.c~pid-namespaces-define-and-use-task_active_pid_ns-wrapper kernel/pid.c --- a/kernel/pid.c~pid-namespaces-define-and-use-task_active_pid_ns-wrapper +++ a/kernel/pid.c @@ -214,7 +214,7 @@ struct pid *alloc_pid(void) int nr = -1; struct pid_namespace *ns; - ns = current->nsproxy->pid_ns; + ns = task_active_pid_ns(current); pid = kmem_cache_alloc(ns->pid_cachep, GFP_KERNEL); if (!pid) goto out; @@ -364,7 +364,7 @@ struct pid *find_ge_pid(int nr) pid = find_pid(nr); if (pid) break; - nr = next_pidmap(current->nsproxy->pid_ns, nr); + nr = next_pidmap(task_active_pid_ns(current), nr); } while (nr > 0); return pid; _