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Commit 2798d4ce authored by Al Viro's avatar Al Viro
Browse files

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: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 215752fc

kernel/acct.c

+52 −33
Original line number Diff line number Diff line
@@ -79,9 +79,14 @@ int acct_parm[3] = {4, 2, 30}; 
static void do_acct_process(struct bsd_acct_struct *acct);



struct bsd_acct_struct {

	long			count;

	atomic_long_t		count;

	union {

		struct {

			struct hlist_node	s_list;

			struct hlist_node	m_list;

		};

		struct rcu_head rcu;

	};

	struct mutex		lock;

	int			active;

	unsigned long		needcheck;
@@ -89,6 +94,11 @@ struct bsd_acct_struct { 
	struct pid_namespace	*ns;

};



static void acct_free_rcu(struct rcu_head *head)

{

	kfree(container_of(head, struct bsd_acct_struct, rcu));

}



static DEFINE_SPINLOCK(acct_lock);



/*
@@ -128,22 +138,22 @@ static int check_free_space(struct bsd_acct_struct *acct) 


static void acct_put(struct bsd_acct_struct *p)

{

	spin_lock(&acct_lock);

	if (!--p->count)

		kfree(p);

	spin_unlock(&acct_lock);

	if (atomic_long_dec_and_test(&p->count))

		call_rcu(&p->rcu, acct_free_rcu);

}



static struct bsd_acct_struct *__acct_get(struct bsd_acct_struct *res)

{

	res->count++;

	spin_unlock(&acct_lock);

	if (!atomic_long_inc_not_zero(&res->count)) {

		rcu_read_unlock();

		cpu_relax();

		return NULL;

	}

	rcu_read_unlock();

	mutex_lock(&res->lock);

	if (!res->ns) {

		mutex_unlock(&res->lock);

		spin_lock(&acct_lock);

		if (!--res->count)

			kfree(res);

		acct_put(res);

		return NULL;

	}

	return res;
@@ -152,13 +162,15 @@ static struct bsd_acct_struct *__acct_get(struct bsd_acct_struct *res) 
static struct bsd_acct_struct *acct_get(struct pid_namespace *ns)

{

	struct bsd_acct_struct *res;

	spin_lock(&acct_lock);

again:

	if (!ns->bacct) {

		spin_unlock(&acct_lock);

	smp_rmb();

	rcu_read_lock();

	res = ACCESS_ONCE(ns->bacct);

	if (!res) {

		rcu_read_unlock();

		return NULL;

	}

	res = __acct_get(ns->bacct);

	res = __acct_get(res);

	if (!res)

		goto again;

	return res;
@@ -170,26 +182,27 @@ static void acct_kill(struct bsd_acct_struct *acct, 
	if (acct) {

		struct file *file = acct->file;

		struct pid_namespace *ns = acct->ns;

		do_acct_process(acct);

		mnt_unpin(file->f_path.mnt);

		filp_close(file, NULL);

		spin_lock(&acct_lock);

		hlist_del(&acct->m_list);

		hlist_del(&acct->s_list);

		mnt_unpin(file->f_path.mnt);

		spin_unlock(&acct_lock);

		do_acct_process(acct);

		filp_close(file, NULL);

		spin_lock(&acct_lock);

		ns->bacct = new;

		if (new) {

			struct vfsmount *m = new->file->f_path.mnt;

			mnt_pin(m);

			spin_lock(&acct_lock);

			hlist_add_head(&new->s_list, &m->mnt_sb->s_pins);

			hlist_add_head(&new->m_list, &real_mount(m)->mnt_pins);

			spin_unlock(&acct_lock);

			mutex_unlock(&new->lock);

		}

		acct->ns = NULL;

		atomic_long_dec(&acct->count);

		mutex_unlock(&acct->lock);

		if (!(acct->count -= 2))

			kfree(acct);

		spin_unlock(&acct_lock);

		acct_put(acct);

	}

}
@@ -223,7 +236,7 @@ static int acct_on(struct filename *pathname) 
		return -EIO;

	}



	acct->count = 1;

	atomic_long_set(&acct->count, 1);

	acct->file = file;

	acct->needcheck = jiffies;

	acct->ns = ns;
@@ -231,15 +244,17 @@ static int acct_on(struct filename *pathname) 
	mnt = file->f_path.mnt;



	old = acct_get(ns);

	mutex_lock_nested(&acct->lock, 1);	/* nobody has seen it yet */

	if (old) {

		acct_kill(old, acct);

	} else {

		spin_lock(&acct_lock);

		ns->bacct = acct;

		spin_lock(&acct_lock);

		mnt_pin(mnt);

		hlist_add_head(&acct->s_list, &mnt->mnt_sb->s_pins);

		hlist_add_head(&acct->m_list, &real_mount(mnt)->mnt_pins);

		spin_unlock(&acct_lock);

		mutex_unlock(&acct->lock);

	}

	mntput(mnt); /* it's pinned, now give up active reference */

	return 0;
@@ -282,28 +297,32 @@ SYSCALL_DEFINE1(acct, const char __user *, name) 


void acct_auto_close_mnt(struct hlist_head *list)

{

	rcu_read_lock();

	while (1) {

		spin_lock(&acct_lock);

		if (!list->first)

		struct hlist_node *p = ACCESS_ONCE(list->first);

		if (!p)

			break;

		acct_kill(__acct_get(hlist_entry(list->first,

		acct_kill(__acct_get(hlist_entry(p,

						 struct bsd_acct_struct,

						 m_list)), NULL);

		rcu_read_lock();

	}

	spin_unlock(&acct_lock);

	rcu_read_unlock();

}



void acct_auto_close(struct hlist_head *list)

{

	rcu_read_lock();

	while (1) {

		spin_lock(&acct_lock);

		if (!list->first)

		struct hlist_node *p = ACCESS_ONCE(list->first);

		if (!p)

			break;

		acct_kill(__acct_get(hlist_entry(list->first,

		acct_kill(__acct_get(hlist_entry(p,

						 struct bsd_acct_struct,

						 s_list)), NULL);

		rcu_read_lock();

	}

	spin_unlock(&acct_lock);

	rcu_read_unlock();

}



void acct_exit_ns(struct pid_namespace *ns)