Messages in this thread Patch in this message | | | Date | Wed, 22 Dec 2010 14:18:50 +0800 | From | Lai Jiangshan <> | Subject | [PATCH 1/4 V3 ] futex,plist: pass the real head of the priority list to plist_del() |
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On 12/22/2010 03:13 AM, Darren Hart wrote: > On 12/21/2010 01:55 AM, Lai Jiangshan wrote: > > Hi Lai, > > Looks about ready to me, only a couple of more nitpics from me. >
Fixed, thanks.
Subject: [PATCH 1/4 V3 ] 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 said that @head is "list head" the head of the priority list.
In futex code, several places use "plist_del(&q->list, &q->list.plist);", they passes faked head, we fix them all.
Thanks to Darren Hart for many suggestions.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> --- diff --git a/kernel/futex.c b/kernel/futex.c index 3019b92..d4f7252 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -740,6 +740,24 @@ 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. @@ -757,7 +775,7 @@ 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 @@ -1066,8 +1084,7 @@ 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; @@ -1470,8 +1487,7 @@ 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); @@ -1491,8 +1507,7 @@ 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); @@ -2133,7 +2148,7 @@ 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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