Commit b6c33652 authored by Alexey Gladkov's avatar Alexey Gladkov Committed by Eric W. Biederman
Browse files

Use atomic_t for ucounts reference counting 



The current implementation of the ucounts reference counter requires the
use of spin_lock. We're going to use get_ucounts() in more performance
critical areas like a handling of RLIMIT_SIGPENDING.

Now we need to use spin_lock only if we want to change the hashtable.

v10:
* Always try to put ucounts in case we cannot increase ucounts->count.
  This will allow to cover the case when all consumers will return
  ucounts at once.

v9:
* Use a negative value to check that the ucounts->count is close to
  overflow.

Signed-off-by: default avatarAlexey Gladkov <legion@kernel.org>
Link: https://lkml.kernel.org/r/94d1dbecab060a6b116b0a2d1accd8ca1bbb4f5f.1619094428.git.legion@kernel.org


Signed-off-by: default avatarEric W. Biederman <ebiederm@xmission.com>
parent 905ae01c

include/linux/user_namespace.h

+2 −2
Original line number Diff line number Diff line
@@ -95,7 +95,7 @@ struct ucounts { 
	struct hlist_node node;

	struct user_namespace *ns;

	kuid_t uid;

	int count;

	atomic_t count;

	atomic_long_t ucount[UCOUNT_COUNTS];

};
@@ -107,7 +107,7 @@ void retire_userns_sysctls(struct user_namespace *ns); 
struct ucounts *inc_ucount(struct user_namespace *ns, kuid_t uid, enum ucount_type type);

void dec_ucount(struct ucounts *ucounts, enum ucount_type type);

struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid);

struct ucounts *get_ucounts(struct ucounts *ucounts);

struct ucounts * __must_check get_ucounts(struct ucounts *ucounts);

void put_ucounts(struct ucounts *ucounts);



#ifdef CONFIG_USER_NS

kernel/ucount.c

+19 −34
Original line number Diff line number Diff line
@@ -11,7 +11,7 @@ 
struct ucounts init_ucounts = {

	.ns    = &init_user_ns,

	.uid   = GLOBAL_ROOT_UID,

	.count = 1,

	.count = ATOMIC_INIT(1),

};



#define UCOUNTS_HASHTABLE_BITS 10
@@ -139,6 +139,15 @@ static void hlist_add_ucounts(struct ucounts *ucounts) 
	spin_unlock_irq(&ucounts_lock);

}



struct ucounts *get_ucounts(struct ucounts *ucounts)

{

	if (ucounts && atomic_add_negative(1, &ucounts->count)) {

		put_ucounts(ucounts);

		ucounts = NULL;

	}

	return ucounts;

}



struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)

{

	struct hlist_head *hashent = ucounts_hashentry(ns, uid);
@@ -155,7 +164,7 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid) 


		new->ns = ns;

		new->uid = uid;

		new->count = 0;

		atomic_set(&new->count, 1);



		spin_lock_irq(&ucounts_lock);

		ucounts = find_ucounts(ns, uid, hashent);
@@ -163,33 +172,12 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid) 
			kfree(new);

		} else {

			hlist_add_head(&new->node, hashent);

			ucounts = new;

		}

	}

	if (ucounts->count == INT_MAX)

		ucounts = NULL;

	else

		ucounts->count += 1;

			spin_unlock_irq(&ucounts_lock);

	return ucounts;

			return new;

		}



struct ucounts *get_ucounts(struct ucounts *ucounts)

{

	unsigned long flags;



	if (!ucounts)

		return NULL;



	spin_lock_irqsave(&ucounts_lock, flags);

	if (ucounts->count == INT_MAX) {

		WARN_ONCE(1, "ucounts: counter has reached its maximum value");

		ucounts = NULL;

	} else {

		ucounts->count += 1;

	}

	spin_unlock_irqrestore(&ucounts_lock, flags);



	spin_unlock_irq(&ucounts_lock);

	ucounts = get_ucounts(ucounts);

	return ucounts;

}
@@ -197,16 +185,13 @@ void put_ucounts(struct ucounts *ucounts) 
{

	unsigned long flags;



	if (atomic_dec_and_test(&ucounts->count)) {

		spin_lock_irqsave(&ucounts_lock, flags);

	ucounts->count -= 1;

	if (!ucounts->count)

		hlist_del_init(&ucounts->node);

	else

		ucounts = NULL;

		spin_unlock_irqrestore(&ucounts_lock, flags);



		kfree(ucounts);

	}

}



static inline bool atomic_long_inc_below(atomic_long_t *v, int u)

{