acct: get rid of acct_lock for acct->count
* make acct->count atomic and acct freeing - rcu-delayed. * instead of grabbing acct_lock around the places where we take a reference, do that under rcu_read_lock() with atomic_long_inc_not_zero(). * have the new acct locked before making ns->bacct point to it Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro
parent
215752fce3
commit
2798d4ce61
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@ -79,9 +79,14 @@ int acct_parm[3] = {4, 2, 30};
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static void do_acct_process(struct bsd_acct_struct *acct);
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struct bsd_acct_struct {
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long count;
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struct hlist_node s_list;
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struct hlist_node m_list;
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atomic_long_t count;
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union {
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struct {
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struct hlist_node s_list;
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struct hlist_node m_list;
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};
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struct rcu_head rcu;
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};
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struct mutex lock;
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int active;
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unsigned long needcheck;
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@ -89,6 +94,11 @@ struct bsd_acct_struct {
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struct pid_namespace *ns;
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};
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static void acct_free_rcu(struct rcu_head *head)
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{
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kfree(container_of(head, struct bsd_acct_struct, rcu));
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}
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static DEFINE_SPINLOCK(acct_lock);
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/*
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@ -128,22 +138,22 @@ out:
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static void acct_put(struct bsd_acct_struct *p)
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{
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spin_lock(&acct_lock);
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if (!--p->count)
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kfree(p);
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spin_unlock(&acct_lock);
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if (atomic_long_dec_and_test(&p->count))
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call_rcu(&p->rcu, acct_free_rcu);
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}
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static struct bsd_acct_struct *__acct_get(struct bsd_acct_struct *res)
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{
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res->count++;
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spin_unlock(&acct_lock);
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if (!atomic_long_inc_not_zero(&res->count)) {
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rcu_read_unlock();
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cpu_relax();
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return NULL;
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}
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rcu_read_unlock();
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mutex_lock(&res->lock);
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if (!res->ns) {
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mutex_unlock(&res->lock);
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spin_lock(&acct_lock);
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if (!--res->count)
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kfree(res);
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acct_put(res);
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return NULL;
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}
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return res;
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@ -152,13 +162,15 @@ static struct bsd_acct_struct *__acct_get(struct bsd_acct_struct *res)
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static struct bsd_acct_struct *acct_get(struct pid_namespace *ns)
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{
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struct bsd_acct_struct *res;
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spin_lock(&acct_lock);
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again:
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if (!ns->bacct) {
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spin_unlock(&acct_lock);
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smp_rmb();
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rcu_read_lock();
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res = ACCESS_ONCE(ns->bacct);
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if (!res) {
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rcu_read_unlock();
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return NULL;
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}
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res = __acct_get(ns->bacct);
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res = __acct_get(res);
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if (!res)
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goto again;
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return res;
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@ -170,26 +182,27 @@ static void acct_kill(struct bsd_acct_struct *acct,
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if (acct) {
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struct file *file = acct->file;
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struct pid_namespace *ns = acct->ns;
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do_acct_process(acct);
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mnt_unpin(file->f_path.mnt);
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filp_close(file, NULL);
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spin_lock(&acct_lock);
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hlist_del(&acct->m_list);
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hlist_del(&acct->s_list);
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mnt_unpin(file->f_path.mnt);
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spin_unlock(&acct_lock);
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do_acct_process(acct);
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filp_close(file, NULL);
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spin_lock(&acct_lock);
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ns->bacct = new;
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if (new) {
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struct vfsmount *m = new->file->f_path.mnt;
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mnt_pin(m);
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spin_lock(&acct_lock);
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hlist_add_head(&new->s_list, &m->mnt_sb->s_pins);
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hlist_add_head(&new->m_list, &real_mount(m)->mnt_pins);
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spin_unlock(&acct_lock);
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mutex_unlock(&new->lock);
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}
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acct->ns = NULL;
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atomic_long_dec(&acct->count);
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mutex_unlock(&acct->lock);
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if (!(acct->count -= 2))
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kfree(acct);
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spin_unlock(&acct_lock);
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acct_put(acct);
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}
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}
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@ -223,7 +236,7 @@ static int acct_on(struct filename *pathname)
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return -EIO;
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}
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acct->count = 1;
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atomic_long_set(&acct->count, 1);
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acct->file = file;
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acct->needcheck = jiffies;
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acct->ns = ns;
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@ -231,15 +244,17 @@ static int acct_on(struct filename *pathname)
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mnt = file->f_path.mnt;
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old = acct_get(ns);
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mutex_lock_nested(&acct->lock, 1); /* nobody has seen it yet */
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if (old) {
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acct_kill(old, acct);
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} else {
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spin_lock(&acct_lock);
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ns->bacct = acct;
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spin_lock(&acct_lock);
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mnt_pin(mnt);
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hlist_add_head(&acct->s_list, &mnt->mnt_sb->s_pins);
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hlist_add_head(&acct->m_list, &real_mount(mnt)->mnt_pins);
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spin_unlock(&acct_lock);
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mutex_unlock(&acct->lock);
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}
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mntput(mnt); /* it's pinned, now give up active reference */
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return 0;
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@ -282,28 +297,32 @@ SYSCALL_DEFINE1(acct, const char __user *, name)
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void acct_auto_close_mnt(struct hlist_head *list)
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{
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rcu_read_lock();
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while (1) {
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spin_lock(&acct_lock);
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if (!list->first)
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struct hlist_node *p = ACCESS_ONCE(list->first);
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if (!p)
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break;
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acct_kill(__acct_get(hlist_entry(list->first,
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acct_kill(__acct_get(hlist_entry(p,
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struct bsd_acct_struct,
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m_list)), NULL);
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rcu_read_lock();
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}
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spin_unlock(&acct_lock);
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rcu_read_unlock();
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}
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void acct_auto_close(struct hlist_head *list)
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{
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rcu_read_lock();
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while (1) {
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spin_lock(&acct_lock);
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if (!list->first)
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struct hlist_node *p = ACCESS_ONCE(list->first);
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if (!p)
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break;
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acct_kill(__acct_get(hlist_entry(list->first,
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acct_kill(__acct_get(hlist_entry(p,
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struct bsd_acct_struct,
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s_list)), NULL);
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rcu_read_lock();
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}
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spin_unlock(&acct_lock);
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rcu_read_unlock();
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}
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void acct_exit_ns(struct pid_namespace *ns)
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