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authorAl Viro <viro@zeniv.linux.org.uk>2014-08-07 07:04:28 -0400
committerAl Viro <viro@zeniv.linux.org.uk>2014-08-07 14:40:08 -0400
commit2798d4ce61601808b965253d60624bbf201b51b0 (patch)
treee938df0fd8040a69da38a277c753aac42272c292
parent215752fce31c80f3b3a1530bc7cddb3ba6a69b3a (diff)
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>
-rw-r--r--kernel/acct.c85
1 files changed, 52 insertions, 33 deletions
diff --git a/kernel/acct.c b/kernel/acct.c
index 21fbb3c27c2a..6fd375f15626 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -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 @@ out:
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)