[PATCH 2/2] move exit_task_namespaces() outside of exit_notify()

From: Oleg Nesterov
Date: Fri Jun 14 2013 - 15:14:05 EST

exit_notify() does exit_task_namespaces() after
forget_original_parent(). This was needed to ensure that ->nsproxy
can't be cleared prematurely, an exiting child we are going to
reparent can do do_notify_parent() and use the parent's (ours) pid_ns.

However, after 32084504 "pidns: use task_active_pid_ns in
do_notify_parent" ->nsproxy != NULL is no longer needed, we rely
on task_active_pid_ns().

Move exit_task_namespaces() from exit_notify() to do_exit(), after
exit_fs() and before exit_task_work().

This solves the problem reported by Andrey, free_ipc_ns()->shm_destroy()
does fput() which needs task_work_add().

Note: this particular problem can be fixed if we change fput(), and
that change makes sense anyway. But there is another reason to move
the callsite. The original reason for exit_task_namespaces() from
the middle of exit_notify() was subtle and it has already gone away,
now this looks confusing. And this allows us do simplify exit_notify(),
we can avoid unlock/lock(tasklist) and we can use ->exit_state instead
of PF_EXITING in forget_original_parent().

Reported-by: Andrey Vagin <avagin@xxxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Acked-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
Acked-by: Andrey Vagin <avagin@xxxxxxxxxx>
kernel/exit.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 8fc3c8f..c623cd3 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -644,7 +644,6 @@ static void exit_notify(struct task_struct *tsk, int group_dead)
* jobs, send them a SIGHUP and then a SIGCONT. (POSIX
- exit_task_namespaces(tsk);

if (group_dead)
@@ -790,6 +789,7 @@ void do_exit(long code)
+ exit_task_namespaces(tsk);

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