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Subject[tip:core/futexes] futex,plist: Pass the real head of the priority list to plist_del()
Commit-ID:  2e12978a9f7a7abd54e8eb9ce70a7718767b8b2c
Gitweb: http://git.kernel.org/tip/2e12978a9f7a7abd54e8eb9ce70a7718767b8b2c
Author: Lai Jiangshan <laijs@cn.fujitsu.com>
AuthorDate: Wed, 22 Dec 2010 14:18:50 +0800
Committer: Steven Rostedt <rostedt@goodmis.org>
CommitDate: Fri, 11 Mar 2011 15:09:52 -0500

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

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>
---
kernel/futex.c | 31 +++++++++++++++++++++++--------
1 files changed, 23 insertions(+), 8 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c
index b766d28..6feeea4 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -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;

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