bsd_acct: using task_struct->tgid is not right in pid-namespaces

In case we're accounting from a sub-namespace, the tgids reported will not
refer to the right namespace.

Save the pid_namespace we're accounting in on the acct_glbs and use it in
do_acct_process.

Two less :) places using the task_struct.tgid member.

Signed-off-by: Pavel Emelyanov <[e-mail]>
Cc: Oleg Nesterov <[e-mail]>
Cc: "Paul E. McKenney" <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

kernel/acct.c

···
 #include <asm/uaccess.h>
 #include <asm/div64.h>
 #include <linux/blkdev.h> /* sector_div */
+#include <linux/pid_namespace.h>
 
 /*
  * These constants control the amount of freespace that suspend and
···
 /*
  * External references and all of the globals.
  */
-static void do_acct_process(struct file *);
+static void do_acct_process(struct pid_namespace *ns, struct file *);
 
 /*
  * This structure is used so that all the data protected by lock
···
 	volatile int		active;
 	volatile int		needcheck;
 	struct file		*file;
+	struct pid_namespace	*ns;
 	struct timer_list	timer;
 };
 
···
 static void acct_file_reopen(struct file *file)
 {
 	struct file *old_acct = NULL;
+	struct pid_namespace *old_ns = NULL;
 
 	if (acct_globals.file) {
 		old_acct = acct_globals.file;
+		old_ns = acct_globals.ns;
 		del_timer(&acct_globals.timer);
 		acct_globals.active = 0;
 		acct_globals.needcheck = 0;
···
 	}
 	if (file) {
 		acct_globals.file = file;
+		acct_globals.ns = get_pid_ns(task_active_pid_ns(current));
 		acct_globals.needcheck = 0;
 		acct_globals.active = 1;
 		/* It's been deleted if it was used before so this is safe */
···
 	if (old_acct) {
 		mnt_unpin(old_acct->f_path.mnt);
 		spin_unlock(&acct_globals.lock);
-		do_acct_process(old_acct);
+		do_acct_process(old_ns, old_acct);
 		filp_close(old_acct, NULL);
+		put_pid_ns(old_ns);
 		spin_lock(&acct_globals.lock);
 	}
 }
···
 /*
  *  do_acct_process does all actual work. Caller holds the reference to file.
  */
-static void do_acct_process(struct file *file)
+static void do_acct_process(struct pid_namespace *ns, struct file *file)
 {
 	struct pacct_struct *pacct = &current->signal->pacct;
 	acct_t ac;
···
 	ac.ac_gid16 = current->gid;
 #endif
 #if ACCT_VERSION==3
-	ac.ac_pid = current->tgid;
+	ac.ac_pid = task_tgid_nr_ns(current, ns);
 	rcu_read_lock();
-	ac.ac_ppid = rcu_dereference(current->real_parent)->tgid;
+	ac.ac_ppid = task_tgid_nr_ns(rcu_dereference(current->real_parent), ns);
 	rcu_read_unlock();
 #endif
 
···
 void acct_process(void)
 {
 	struct file *file = NULL;
+	struct pid_namespace *ns;
 
 	/*
 	 * accelerate the common fastpath:
···
 		return;
 	}
 	get_file(file);
+	ns = get_pid_ns(acct_globals.ns);
 	spin_unlock(&acct_globals.lock);
 
-	do_acct_process(file);
+	do_acct_process(ns, file);
 	fput(file);
+	put_pid_ns(ns);
 }