new fs_pin killing logics

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

diff --git a/fs/fs_pin.c b/fs/fs_pin.c
index 50ef7d2..0c77bdc 100644 (file)
--- 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 2be38d1..9dc4e03 100644 (file)
--- 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 b9cf6c5..918b117 100644 (file)
--- 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 cf6588a..e6c10d1 100644 (file)
--- 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);
 }
 
 /*