Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 3fa97c9d authored by Andrew Morton's avatar Andrew Morton Committed by Linus Torvalds
Browse files

[PATCH] "Fix uidhash_lock <-> RXU deadlock" fix 



I get storms of warnings from local_bh_enable().  Better-tested patches,
please.

Cc: Ingo Molnar <mingo@elte.hu>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent b8c475be

kernel/user.c

+17 −10
Original line number Original line Diff line number Diff line
@@ -33,6 +33,10 @@ static struct list_head uidhash_table[UIDHASH_SZ]; 
 * The uidhash_lock is mostly taken from process context, but it is

 * The uidhash_lock is mostly taken from process context, but it is

 * occasionally also taken from softirq/tasklet context, when

 * occasionally also taken from softirq/tasklet context, when

 * task-structs get RCU-freed. Hence all locking must be softirq-safe.

 * task-structs get RCU-freed. Hence all locking must be softirq-safe.

 * But free_uid() is also called with local interrupts disabled, and running

 * local_bh_enable() with local interrupts disabled is an error - we'll run

 * softirq callbacks, and they can unconditionally enable interrupts, and

 * the caller of free_uid() didn't expect that..

 */

 */

static DEFINE_SPINLOCK(uidhash_lock);

static DEFINE_SPINLOCK(uidhash_lock);
@@ -89,16 +93,19 @@ static inline struct user_struct *uid_hash_find(uid_t uid, struct list_head *has 
struct user_struct *find_user(uid_t uid)

struct user_struct *find_user(uid_t uid)

{

{

	struct user_struct *ret;

	struct user_struct *ret;

	unsigned long flags;





	spin_lock_bh(&uidhash_lock);

	spin_lock_irqsave(&uidhash_lock, flags);

	ret = uid_hash_find(uid, uidhashentry(uid));

	ret = uid_hash_find(uid, uidhashentry(uid));

	spin_unlock_bh(&uidhash_lock);

	spin_unlock_irqrestore(&uidhash_lock, flags);

	return ret;

	return ret;

}

}





void free_uid(struct user_struct *up)

void free_uid(struct user_struct *up)

{

{

	local_bh_disable();

	unsigned long flags;



	local_irq_save(flags);

	if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {

	if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {

		uid_hash_remove(up);

		uid_hash_remove(up);

		key_put(up->uid_keyring);

		key_put(up->uid_keyring);
@@ -106,7 +113,7 @@ void free_uid(struct user_struct *up) 
		kmem_cache_free(uid_cachep, up);

		kmem_cache_free(uid_cachep, up);

		spin_unlock(&uidhash_lock);

		spin_unlock(&uidhash_lock);

	}

	}

	local_bh_enable();

	local_irq_restore(flags);

}

}





struct user_struct * alloc_uid(uid_t uid)

struct user_struct * alloc_uid(uid_t uid)
@@ -114,9 +121,9 @@ struct user_struct * alloc_uid(uid_t uid) 
	struct list_head *hashent = uidhashentry(uid);

	struct list_head *hashent = uidhashentry(uid);

	struct user_struct *up;

	struct user_struct *up;





	spin_lock_bh(&uidhash_lock);

	spin_lock_irq(&uidhash_lock);

	up = uid_hash_find(uid, hashent);

	up = uid_hash_find(uid, hashent);

	spin_unlock_bh(&uidhash_lock);

	spin_unlock_irq(&uidhash_lock);





	if (!up) {

	if (!up) {

		struct user_struct *new;

		struct user_struct *new;
@@ -146,7 +153,7 @@ struct user_struct * alloc_uid(uid_t uid) 
		 * Before adding this, check whether we raced

		 * Before adding this, check whether we raced

		 * on adding the same user already..

		 * on adding the same user already..

		 */

		 */

		spin_lock_bh(&uidhash_lock);

		spin_lock_irq(&uidhash_lock);

		up = uid_hash_find(uid, hashent);

		up = uid_hash_find(uid, hashent);

		if (up) {

		if (up) {

			key_put(new->uid_keyring);

			key_put(new->uid_keyring);
@@ -156,7 +163,7 @@ struct user_struct * alloc_uid(uid_t uid) 
			uid_hash_insert(new, hashent);

			uid_hash_insert(new, hashent);

			up = new;

			up = new;

		}

		}

		spin_unlock_bh(&uidhash_lock);

		spin_unlock_irq(&uidhash_lock);





	}

	}

	return up;

	return up;
@@ -192,9 +199,9 @@ static int __init uid_cache_init(void) 
		INIT_LIST_HEAD(uidhash_table + n);

		INIT_LIST_HEAD(uidhash_table + n);





	/* Insert the root user immediately (init already runs as root) */

	/* Insert the root user immediately (init already runs as root) */

	spin_lock_bh(&uidhash_lock);

	spin_lock_irq(&uidhash_lock);

	uid_hash_insert(&root_user, uidhashentry(0));

	uid_hash_insert(&root_user, uidhashentry(0));

	spin_unlock_bh(&uidhash_lock);

	spin_unlock_irq(&uidhash_lock);





	return 0;

	return 0;

}

}