new fs_pin killing logics

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 34 insertions, 47 deletions

diff --git a/kernel/acct.c b/kernel/acct.c
index cf6588ab517b..e6c10d1a4058 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -76,7 +76,6 @@ int acct_parm[3] = {4, 2, 30};
 /*
  * External references and all of the globals.
  */
-static void do_acct_process(struct bsd_acct_struct *acct);
 
 struct bsd_acct_struct {
         struct fs_pin           pin;
@@ -91,6 +90,8 @@ struct bsd_acct_struct {
         struct completion       done;
 };
 
+static void do_acct_process(struct bsd_acct_struct *acct);
+
 /*
  * Check the amount of free space and suspend/resume accordingly.
  */
@@ -132,13 +133,18 @@ static void acct_put(struct bsd_acct_struct *p)
                 kfree_rcu(p, rcu);
 }
 
+static inline struct bsd_acct_struct *to_acct(struct fs_pin *p)
+{
+        return p ? container_of(p, struct bsd_acct_struct, pin) : NULL;
+}
+
 static struct bsd_acct_struct *acct_get(struct pid_namespace *ns)
 {
         struct bsd_acct_struct *res;
 again:
         smp_rmb();
         rcu_read_lock();
-        res = ACCESS_ONCE(ns->bacct);
+        res = to_acct(ACCESS_ONCE(ns->bacct));
         if (!res) {
                 rcu_read_unlock();
                 return NULL;
@@ -150,7 +156,7 @@ again:
         }
         rcu_read_unlock();
         mutex_lock(&res->lock);
-        if (!res->ns) {
+        if (res != to_acct(ACCESS_ONCE(ns->bacct))) {
                 mutex_unlock(&res->lock);
                 acct_put(res);
                 goto again;
@@ -158,6 +164,19 @@ again:
         return res;
 }
 
+static void acct_pin_kill(struct fs_pin *pin)
+{
+        struct bsd_acct_struct *acct = to_acct(pin);
+        mutex_lock(&acct->lock);
+        do_acct_process(acct);
+        schedule_work(&acct->work);
+        wait_for_completion(&acct->done);
+        cmpxchg(&acct->ns->bacct, pin, NULL);
+        mutex_unlock(&acct->lock);
+        pin_remove(pin);
+        acct_put(acct);
+}
+
 static void close_work(struct work_struct *work)
 {
         struct bsd_acct_struct *acct = container_of(work, struct bsd_acct_struct, work);
@@ -168,49 +187,13 @@ static void close_work(struct work_struct *work)
         complete(&acct->done);
 }
 
-static void acct_kill(struct bsd_acct_struct *acct)
-{
-        if (acct) {
-                struct pid_namespace *ns = acct->ns;
-                do_acct_process(acct);
-                INIT_WORK(&acct->work, close_work);
-                init_completion(&acct->done);
-                schedule_work(&acct->work);
-                wait_for_completion(&acct->done);
-                pin_remove(&acct->pin);
-                cmpxchg(&ns->bacct, acct, NULL);
-                acct->ns = NULL;
-                atomic_long_dec(&acct->count);
-                mutex_unlock(&acct->lock);
-                acct_put(acct);
-        }
-}
-
-static void acct_pin_kill(struct fs_pin *pin)
-{
-        struct bsd_acct_struct *acct;
-        acct = container_of(pin, struct bsd_acct_struct, pin);
-        if (!atomic_long_inc_not_zero(&acct->count)) {
-                rcu_read_unlock();
-                cpu_relax();
-                return;
-        }
-        rcu_read_unlock();
-        mutex_lock(&acct->lock);
-        if (!acct->ns) {
-                mutex_unlock(&acct->lock);
-                acct_put(acct);
-                acct = NULL;
-        }
-        acct_kill(acct);
-}
-
 static int acct_on(struct filename *pathname)
 {
         struct file *file;
         struct vfsmount *mnt, *internal;
         struct pid_namespace *ns = task_active_pid_ns(current);
-        struct bsd_acct_struct *acct, *old;
+        struct bsd_acct_struct *acct;
+        struct fs_pin *old;
         int err;
 
         acct = kzalloc(sizeof(struct bsd_acct_struct), GFP_KERNEL);
@@ -252,18 +235,20 @@ static int acct_on(struct filename *pathname)
         file->f_path.mnt = internal;
 
         atomic_long_set(&acct->count, 1);
-        acct->pin.kill = acct_pin_kill;
+        init_fs_pin(&acct->pin, acct_pin_kill);
         acct->file = file;
         acct->needcheck = jiffies;
         acct->ns = ns;
         mutex_init(&acct->lock);
+        INIT_WORK(&acct->work, close_work);
+        init_completion(&acct->done);
         mutex_lock_nested(&acct->lock, 1);      /* nobody has seen it yet */
         pin_insert(&acct->pin, mnt);
 
-        old = acct_get(ns);
-        ns->bacct = acct;
-        acct_kill(old);
+        rcu_read_lock();
+        old = xchg(&ns->bacct, &acct->pin);
         mutex_unlock(&acct->lock);
+        pin_kill(old);
         mnt_drop_write(mnt);
         mntput(mnt);
         return 0;
@@ -299,7 +284,8 @@ SYSCALL_DEFINE1(acct, const char __user *, name)
                 mutex_unlock(&acct_on_mutex);
                 putname(tmp);
         } else {
-                acct_kill(acct_get(task_active_pid_ns(current)));
+                rcu_read_lock();
+                pin_kill(task_active_pid_ns(current)->bacct);
         }
 
         return error;
@@ -307,7 +293,8 @@ SYSCALL_DEFINE1(acct, const char __user *, name)
 
 void acct_exit_ns(struct pid_namespace *ns)
 {
-        acct_kill(acct_get(ns));
+        rcu_read_lock();
+        pin_kill(ns->bacct);
 }
 
 /*