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futex,plist: Pass the real head of the priority list to plist_del()

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Some plist_del()s in kernel/futex.c are passed a faked head of the
priority list.

It does not fail because the current code does not require the real head
in plist_del(). The current code of plist_del() just uses the head for checking,
so it will not cause a bad result even when we use a faked head.

But it is undocumented usage:

/**
 * plist_del - Remove a @node from plist.
 *
 * @node:	&struct plist_node pointer - entry to be removed
 * @head:	&struct plist_head pointer - list head
 */

The document says that the @head is the "list head" head of the priority list.

In futex code, several places use "plist_del(&q->list, &q->list.plist);",
they pass a fake head. We need to fix them all.

Thanks to Darren Hart for many suggestions.

Acked-by: Darren Hart <dvhart@linux.intel.com>
Signed-off-by:  Lai Jiangshan <laijs@cn.fujitsu.com>
LKML-Reference: <4D11984A.5030203@cn.fujitsu.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Lai Jiangshan 2010-12-22 14:18:50 +08:00 committed by Steven Rostedt
parent a5abba989d
commit 2e12978a9f
1 changed files with 23 additions and 8 deletions
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31
kernel/futex.c
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@ -775,6 +775,24 @@ retry:
return ret;
}
/**
* __unqueue_futex() - Remove the futex_q from its futex_hash_bucket
* @q: The futex_q to unqueue
*
* The q->lock_ptr must not be NULL and must be held by the caller.
*/
static void __unqueue_futex(struct futex_q *q)
{
struct futex_hash_bucket *hb;
if (WARN_ON(!q->lock_ptr || !spin_is_locked(q->lock_ptr)
|| plist_node_empty(&q->list)))
return;
hb = container_of(q->lock_ptr, struct futex_hash_bucket, lock);
plist_del(&q->list, &hb->chain);
}
/*
* The hash bucket lock must be held when this is called.
* Afterwards, the futex_q must not be accessed.
@ -792,7 +810,7 @@ static void wake_futex(struct futex_q *q)
*/
get_task_struct(p);
plist_del(&q->list, &q->list.plist);
__unqueue_futex(q);
/*
* The waiting task can free the futex_q as soon as
* q->lock_ptr = NULL is written, without taking any locks. A
@ -1100,8 +1118,7 @@ void requeue_pi_wake_futex(struct futex_q *q, union futex_key *key,
get_futex_key_refs(key);
q->key = *key;
WARN_ON(plist_node_empty(&q->list));
plist_del(&q->list, &q->list.plist);
__unqueue_futex(q);
WARN_ON(!q->rt_waiter);
q->rt_waiter = NULL;
@ -1504,8 +1521,7 @@ retry:
spin_unlock(lock_ptr);
goto retry;
}
WARN_ON(plist_node_empty(&q->list));
plist_del(&q->list, &q->list.plist);
__unqueue_futex(q);
BUG_ON(q->pi_state);
@ -1525,8 +1541,7 @@ retry:
static void unqueue_me_pi(struct futex_q *q)
__releases(q->lock_ptr)
{
WARN_ON(plist_node_empty(&q->list));
plist_del(&q->list, &q->list.plist);
__unqueue_futex(q);
BUG_ON(!q->pi_state);
free_pi_state(q->pi_state);
@ -2167,7 +2182,7 @@ int handle_early_requeue_pi_wakeup(struct futex_hash_bucket *hb,
* We were woken prior to requeue by a timeout or a signal.
* Unqueue the futex_q and determine which it was.
*/
plist_del(&q->list, &q->list.plist);
plist_del(&q->list, &hb->chain);
/* Handle spurious wakeups gracefully */
ret = -EWOULDBLOCK;