bsdacct: switch from global bsd_acct_struct instance to per-pidns one

Allocate the structure on the first call to sys_acct(). After this each
namespace, that ordered the accounting, will live with this structure till
its own death.

Two notes
- routines, that close the accounting on fs umount time use
the init_pid_ns's acct by now;
- accounting routine accounts to dying task's namespace
(also by now).

Signed-off-by: Pavel Emelyanov <[e-mail]>
Cc: Balbir Singh <[e-mail]>
Cc: "Eric W. Biederman" <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/acct.h

···
 struct vfsmount;
 struct super_block;
 struct pacct_struct;
+struct pid_namespace;
 extern void acct_auto_close_mnt(struct vfsmount *m);
 extern void acct_auto_close(struct super_block *sb);
 extern void acct_init_pacct(struct pacct_struct *pacct);
 extern void acct_collect(long exitcode, int group_dead);
 extern void acct_process(void);
+extern void acct_exit_ns(struct pid_namespace *);
 #else
 #define acct_auto_close_mnt(x)	do { } while (0)
 #define acct_auto_close(x)	do { } while (0)
 #define acct_init_pacct(x)	do { } while (0)
 #define acct_collect(x,y)	do { } while (0)
 #define acct_process()		do { } while (0)
+#define acct_exit_ns(ns)	do { } while (0)
 #endif
 
 /*

kernel/acct.c

···
 
 static DEFINE_SPINLOCK(acct_lock);
 
-static struct bsd_acct_struct acct_globals __cacheline_aligned;
-
 /*
  * Called whenever the timer says to check the free space.
  */
···
  *
  * NOTE: acct_lock MUST be held on entry and exit.
  */
-static void acct_file_reopen(struct bsd_acct_struct *acct, struct file *file)
+static void acct_file_reopen(struct bsd_acct_struct *acct, struct file *file,
+		struct pid_namespace *ns)
 {
 	struct file *old_acct = NULL;
 	struct pid_namespace *old_ns = NULL;
···
 		acct->active = 0;
 		acct->needcheck = 0;
 		acct->file = NULL;
+		acct->ns = NULL;
 	}
 	if (file) {
 		acct->file = file;
-		acct->ns = get_pid_ns(task_active_pid_ns(current));
+		acct->ns = ns;
 		acct->needcheck = 0;
 		acct->active = 1;
 		/* It's been deleted if it was used before so this is safe */
···
 		spin_unlock(&acct_lock);
 		do_acct_process(acct, old_ns, old_acct);
 		filp_close(old_acct, NULL);
-		put_pid_ns(old_ns);
 		spin_lock(&acct_lock);
 	}
 }
···
 {
 	struct file *file;
 	int error;
+	struct pid_namespace *ns;
+	struct bsd_acct_struct *acct = NULL;
 
 	/* Difference from BSD - they don't do O_APPEND */
 	file = filp_open(name, O_WRONLY|O_APPEND|O_LARGEFILE, 0);
···
 		return -EIO;
 	}
 
+	ns = task_active_pid_ns(current);
+	if (ns->bacct == NULL) {
+		acct = kzalloc(sizeof(struct bsd_acct_struct), GFP_KERNEL);
+		if (acct == NULL) {
+			filp_close(file, NULL);
+			return -ENOMEM;
+		}
+	}
+
 	error = security_acct(file);
 	if (error) {
+		kfree(acct);
 		filp_close(file, NULL);
 		return error;
 	}
 
 	spin_lock(&acct_lock);
+	if (ns->bacct == NULL) {
+		ns->bacct = acct;
+		acct = NULL;
+	}
+
 	mnt_pin(file->f_path.mnt);
-	acct_file_reopen(&acct_globals, file);
+	acct_file_reopen(ns->bacct, file, ns);
 	spin_unlock(&acct_lock);
 
 	mntput(file->f_path.mnt); /* it's pinned, now give up active reference */
+	kfree(acct);
 
 	return 0;
 }
···
 		error = acct_on(tmp);
 		putname(tmp);
 	} else {
+		struct bsd_acct_struct *acct;
+
+		acct = task_active_pid_ns(current)->bacct;
+		if (acct == NULL)
+			return 0;
+
 		error = security_acct(NULL);
 		if (!error) {
 			spin_lock(&acct_lock);
-			acct_file_reopen(&acct_globals, NULL);
+			acct_file_reopen(acct, NULL, NULL);
 			spin_unlock(&acct_lock);
 		}
 	}
···
  */
 void acct_auto_close_mnt(struct vfsmount *m)
 {
+	struct bsd_acct_struct *acct;
+
+	acct = init_pid_ns.bacct;
+	if (acct == NULL)
+		return;
+
 	spin_lock(&acct_lock);
-	if (acct_globals.file && acct_globals.file->f_path.mnt == m)
-		acct_file_reopen(&acct_globals, NULL);
+	if (acct->file && acct->file->f_path.mnt == m)
+		acct_file_reopen(acct, NULL, NULL);
 	spin_unlock(&acct_lock);
 }
 
···
  */
 void acct_auto_close(struct super_block *sb)
 {
+	struct bsd_acct_struct *acct;
+
+	acct = init_pid_ns.bacct;
+	if (acct == NULL)
+		return;
+
 	spin_lock(&acct_lock);
-	if (acct_globals.file &&
-	    acct_globals.file->f_path.mnt->mnt_sb == sb) {
-		acct_file_reopen(&acct_globals, NULL);
+	if (acct->file && acct->file->f_path.mnt->mnt_sb == sb)
+		acct_file_reopen(acct, NULL, NULL);
+	spin_unlock(&acct_lock);
+}
+
+void acct_exit_ns(struct pid_namespace *ns)
+{
+	struct bsd_acct_struct *acct;
+
+	spin_lock(&acct_lock);
+	acct = ns->bacct;
+	if (acct != NULL) {
+		if (acct->file != NULL)
+			acct_file_reopen(acct, NULL, NULL);
+
+		kfree(acct);
 	}
 	spin_unlock(&acct_lock);
 }
···
 void acct_process(void)
 {
 	struct file *file = NULL;
-	struct pid_namespace *ns;
+	struct pid_namespace *ns = task_active_pid_ns(current);
+	struct bsd_acct_struct *acct;
 
+	acct = ns->bacct;
 	/*
 	 * accelerate the common fastpath:
 	 */
-	if (!acct_globals.file)
+	if (!acct || !acct->file)
 		return;
 
 	spin_lock(&acct_lock);
-	file = acct_globals.file;
+	file = acct->file;
 	if (unlikely(!file)) {
 		spin_unlock(&acct_lock);
 		return;
 	}
 	get_file(file);
-	ns = get_pid_ns(acct_globals.ns);
 	spin_unlock(&acct_lock);
 
-	do_acct_process(&acct_globals, ns, file);
+	do_acct_process(acct, ns, file);
 	fput(file);
-	put_pid_ns(ns);
 }

kernel/pid_namespace.c

···
 #include <linux/pid_namespace.h>
 #include <linux/syscalls.h>
 #include <linux/err.h>
+#include <linux/acct.h>
 
 #define BITS_PER_PAGE		(PAGE_SIZE*8)
 
···
 
 	/* Child reaper for the pid namespace is going away */
 	pid_ns->child_reaper = NULL;
+	acct_exit_ns(pid_ns);
 	return;
 }