new fs_pin killing logics

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

4 files changed, 96 insertions, 56 deletions

diff --git a/fs/fs_pin.c b/fs/fs_pin.c
index 50ef7d2ef03c..0c77bdc238b2 100644
--- a/fs/fs_pin.c
+++ b/fs/fs_pin.c
@@ -1,4 +1,5 @@
 #include <linux/fs.h>
+#include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/fs_pin.h>
 #include "internal.h"
@@ -12,6 +13,10 @@ void pin_remove(struct fs_pin *pin)
         hlist_del(&pin->m_list);
         hlist_del(&pin->s_list);
         spin_unlock(&pin_lock);
+        spin_lock_irq(&pin->wait.lock);
+        pin->done = 1;
+        wake_up_locked(&pin->wait);
+        spin_unlock_irq(&pin->wait.lock);
 }
 
 void pin_insert_group(struct fs_pin *pin, struct vfsmount *m, struct hlist_head *p)
@@ -28,19 +33,58 @@ void pin_insert(struct fs_pin *pin, struct vfsmount *m)
         pin_insert_group(pin, m, &m->mnt_sb->s_pins);
 }
 
+void pin_kill(struct fs_pin *p)
+{
+        wait_queue_t wait;
+
+        if (!p) {
+                rcu_read_unlock();
+                return;
+        }
+        init_wait(&wait);
+        spin_lock_irq(&p->wait.lock);
+        if (likely(!p->done)) {
+                p->done = -1;
+                spin_unlock_irq(&p->wait.lock);
+                rcu_read_unlock();
+                p->kill(p);
+                return;
+        }
+        if (p->done > 0) {
+                spin_unlock_irq(&p->wait.lock);
+                rcu_read_unlock();
+                return;
+        }
+        __add_wait_queue(&p->wait, &wait);
+        while (1) {
+                set_current_state(TASK_UNINTERRUPTIBLE);
+                spin_unlock_irq(&p->wait.lock);
+                rcu_read_unlock();
+                schedule();
+                rcu_read_lock();
+                if (likely(list_empty(&wait.task_list)))
+                        break;
+                /* OK, we know p couldn't have been freed yet */
+                spin_lock_irq(&p->wait.lock);
+                if (p->done > 0) {
+                        spin_unlock_irq(&p->wait.lock);
+                        break;
+                }
+        }
+        rcu_read_unlock();
+}
+
 void mnt_pin_kill(struct mount *m)
 {
         while (1) {
                 struct hlist_node *p;
-                struct fs_pin *pin;
                 rcu_read_lock();
                 p = ACCESS_ONCE(m->mnt_pins.first);
                 if (!p) {
                         rcu_read_unlock();
                         break;
                 }
-                pin = hlist_entry(p, struct fs_pin, m_list);
-                pin->kill(pin);
+                pin_kill(hlist_entry(p, struct fs_pin, m_list));
         }
 }
 
@@ -48,14 +92,12 @@ void group_pin_kill(struct hlist_head *p)
 {
         while (1) {
                 struct hlist_node *q;
-                struct fs_pin *pin;
                 rcu_read_lock();
                 q = ACCESS_ONCE(p->first);
                 if (!q) {
                         rcu_read_unlock();
                         break;
                 }
-                pin = hlist_entry(q, struct fs_pin, s_list);
-                pin->kill(pin);
+                pin_kill(hlist_entry(q, struct fs_pin, s_list));
         }
 }
diff --git a/include/linux/fs_pin.h b/include/linux/fs_pin.h
index 2be38d1464ae..9dc4e0384bfb 100644
--- a/include/linux/fs_pin.h
+++ b/include/linux/fs_pin.h
@@ -1,11 +1,22 @@
-#include <linux/fs.h>
+#include <linux/wait.h>
 
 struct fs_pin {
+        wait_queue_head_t       wait;
+        int                     done;
         struct hlist_node       s_list;
         struct hlist_node       m_list;
         void (*kill)(struct fs_pin *);
 };
 
+struct vfsmount;
+
+static inline void init_fs_pin(struct fs_pin *p, void (*kill)(struct fs_pin *))
+{
+        init_waitqueue_head(&p->wait);
+        p->kill = kill;
+}
+
 void pin_remove(struct fs_pin *);
 void pin_insert_group(struct fs_pin *, struct vfsmount *, struct hlist_head *);
 void pin_insert(struct fs_pin *, struct vfsmount *);
+void pin_kill(struct fs_pin *);
diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index b9cf6c51b181..918b117a7cd3 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -19,7 +19,7 @@ struct pidmap {
 #define BITS_PER_PAGE_MASK      (BITS_PER_PAGE-1)
 #define PIDMAP_ENTRIES          ((PID_MAX_LIMIT+BITS_PER_PAGE-1)/BITS_PER_PAGE)
 
-struct bsd_acct_struct;
+struct fs_pin;
 
 struct pid_namespace {
         struct kref kref;
@@ -37,7 +37,7 @@ struct pid_namespace {
         struct dentry *proc_thread_self;
 #endif
 #ifdef CONFIG_BSD_PROCESS_ACCT
-        struct bsd_acct_struct *bacct;
+        struct fs_pin *bacct;
 #endif
         struct user_namespace *user_ns;
         struct work_struct proc_work;
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);
 }
 
 /*