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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); static void do_acct_process(struct bsd_acct_struct *acct);
struct bsd_acct_struct { struct bsd_acct_struct {
long count; atomic_long_t count;
struct hlist_node s_list; union {
struct hlist_node m_list; struct {
struct hlist_node s_list;
struct hlist_node m_list;
};
struct rcu_head rcu;
};
struct mutex lock; struct mutex lock;
int active; int active;
unsigned long needcheck; unsigned long needcheck;
@ -89,6 +94,11 @@ struct bsd_acct_struct {
struct pid_namespace *ns; 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); static DEFINE_SPINLOCK(acct_lock);
/* /*
@ -128,22 +138,22 @@ out:
static void acct_put(struct bsd_acct_struct *p) static void acct_put(struct bsd_acct_struct *p)
{ {
spin_lock(&acct_lock); if (atomic_long_dec_and_test(&p->count))
if (!--p->count) call_rcu(&p->rcu, acct_free_rcu);
kfree(p);
spin_unlock(&acct_lock);
} }
static struct bsd_acct_struct *__acct_get(struct bsd_acct_struct *res) static struct bsd_acct_struct *__acct_get(struct bsd_acct_struct *res)
{ {
res->count++; if (!atomic_long_inc_not_zero(&res->count)) {
spin_unlock(&acct_lock); rcu_read_unlock();
cpu_relax();
return NULL;
}
rcu_read_unlock();
mutex_lock(&res->lock); mutex_lock(&res->lock);
if (!res->ns) { if (!res->ns) {
mutex_unlock(&res->lock); mutex_unlock(&res->lock);
spin_lock(&acct_lock); acct_put(res);
if (!--res->count)
kfree(res);
return NULL; return NULL;
} }
return res; 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) static struct bsd_acct_struct *acct_get(struct pid_namespace *ns)
{ {
struct bsd_acct_struct *res; struct bsd_acct_struct *res;
spin_lock(&acct_lock);
again: again:
if (!ns->bacct) { smp_rmb();
spin_unlock(&acct_lock); rcu_read_lock();
res = ACCESS_ONCE(ns->bacct);
if (!res) {
rcu_read_unlock();
return NULL; return NULL;
} }
res = __acct_get(ns->bacct); res = __acct_get(res);
if (!res) if (!res)
goto again; goto again;
return res; return res;
@ -170,26 +182,27 @@ static void acct_kill(struct bsd_acct_struct *acct,
if (acct) { if (acct) {
struct file *file = acct->file; struct file *file = acct->file;
struct pid_namespace *ns = acct->ns; struct pid_namespace *ns = acct->ns;
do_acct_process(acct);
mnt_unpin(file->f_path.mnt);
filp_close(file, NULL);
spin_lock(&acct_lock); spin_lock(&acct_lock);
hlist_del(&acct->m_list); hlist_del(&acct->m_list);
hlist_del(&acct->s_list); hlist_del(&acct->s_list);
mnt_unpin(file->f_path.mnt);
spin_unlock(&acct_lock); spin_unlock(&acct_lock);
do_acct_process(acct);
filp_close(file, NULL);
spin_lock(&acct_lock);
ns->bacct = new; ns->bacct = new;
if (new) { if (new) {
struct vfsmount *m = new->file->f_path.mnt; struct vfsmount *m = new->file->f_path.mnt;
mnt_pin(m); mnt_pin(m);
spin_lock(&acct_lock);
hlist_add_head(&new->s_list, &m->mnt_sb->s_pins); hlist_add_head(&new->s_list, &m->mnt_sb->s_pins);
hlist_add_head(&new->m_list, &real_mount(m)->mnt_pins); hlist_add_head(&new->m_list, &real_mount(m)->mnt_pins);
spin_unlock(&acct_lock);
mutex_unlock(&new->lock);
} }
acct->ns = NULL; acct->ns = NULL;
atomic_long_dec(&acct->count);
mutex_unlock(&acct->lock); mutex_unlock(&acct->lock);
if (!(acct->count -= 2)) acct_put(acct);
kfree(acct);
spin_unlock(&acct_lock);
} }
} }
@ -223,7 +236,7 @@ static int acct_on(struct filename *pathname)
return -EIO; return -EIO;
} }
acct->count = 1; atomic_long_set(&acct->count, 1);
acct->file = file; acct->file = file;
acct->needcheck = jiffies; acct->needcheck = jiffies;
acct->ns = ns; acct->ns = ns;
@ -231,15 +244,17 @@ static int acct_on(struct filename *pathname)
mnt = file->f_path.mnt; mnt = file->f_path.mnt;
old = acct_get(ns); old = acct_get(ns);
mutex_lock_nested(&acct->lock, 1); /* nobody has seen it yet */
if (old) { if (old) {
acct_kill(old, acct); acct_kill(old, acct);
} else { } else {
spin_lock(&acct_lock);
ns->bacct = acct; ns->bacct = acct;
spin_lock(&acct_lock);
mnt_pin(mnt); mnt_pin(mnt);
hlist_add_head(&acct->s_list, &mnt->mnt_sb->s_pins); hlist_add_head(&acct->s_list, &mnt->mnt_sb->s_pins);
hlist_add_head(&acct->m_list, &real_mount(mnt)->mnt_pins); hlist_add_head(&acct->m_list, &real_mount(mnt)->mnt_pins);
spin_unlock(&acct_lock); spin_unlock(&acct_lock);
mutex_unlock(&acct->lock);
} }
mntput(mnt); /* it's pinned, now give up active reference */ mntput(mnt); /* it's pinned, now give up active reference */
return 0; return 0;
@ -282,28 +297,32 @@ SYSCALL_DEFINE1(acct, const char __user *, name)
void acct_auto_close_mnt(struct hlist_head *list) void acct_auto_close_mnt(struct hlist_head *list)
{ {
rcu_read_lock();
while (1) { while (1) {
spin_lock(&acct_lock); struct hlist_node *p = ACCESS_ONCE(list->first);
if (!list->first) if (!p)
break; break;
acct_kill(__acct_get(hlist_entry(list->first, acct_kill(__acct_get(hlist_entry(p,
struct bsd_acct_struct, struct bsd_acct_struct,
m_list)), NULL); m_list)), NULL);
rcu_read_lock();
} }
spin_unlock(&acct_lock); rcu_read_unlock();
} }
void acct_auto_close(struct hlist_head *list) void acct_auto_close(struct hlist_head *list)
{ {
rcu_read_lock();
while (1) { while (1) {
spin_lock(&acct_lock); struct hlist_node *p = ACCESS_ONCE(list->first);
if (!list->first) if (!p)
break; break;
acct_kill(__acct_get(hlist_entry(list->first, acct_kill(__acct_get(hlist_entry(p,
struct bsd_acct_struct, struct bsd_acct_struct,
s_list)), NULL); s_list)), NULL);
rcu_read_lock();
} }
spin_unlock(&acct_lock); rcu_read_unlock();
} }
void acct_exit_ns(struct pid_namespace *ns) void acct_exit_ns(struct pid_namespace *ns)