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acct: get rid of acct_lock for acct->count

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* 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 2014-08-07 07:04:28 -04:00
parent 215752fce3
commit 2798d4ce61
1 changed files with 52 additions and 33 deletions
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85
kernel/acct.c
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@ -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;
struct hlist_node s_list;
struct hlist_node m_list;
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)