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Date: Mon, 02 Mar 2009 16:14:59 -0800
From: Darren Hart <dvhltc@...ibm.com>
To: "lkml, " <linux-kernel@...r.kernel.org>
CC: Thomas Gleixner <tglx@...utronix.de>,
Steven Rostedt <srostedt@...hat.com>,
Sripathi Kodi <sripathik@...ibm.com>,
John Stultz <johnstul@...ux.vnet.ibm.com>
Subject: [TIP][RFC 4/7] futex: finish_futex_lock_pi()
From: Darren Hart <dvhltc@...ibm.com>
Refactor the post lock acquisition logic from futex_lock_pi(). This code will
be reused in futex_wait_requeue_pi().
V4: -Corrected string paranoia check
-Move the spinlock(q->lock_ptr) out of finish_futex_lock_pi to retain
some semblance of lock/unlock in the same function.
V3: -Initial version
Signed-off-by: Darren Hart <dvhltc@...ibm.com>
---
kernel/futex.c | 146 ++++++++++++++++++++++++++++++--------------------------
1 files changed, 78 insertions(+), 68 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c
index c4984d4..9446494 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1303,6 +1303,81 @@ handle_fault:
static long futex_wait_restart(struct restart_block *restart);
+/* finish_futex_lock_pi - post lock pi_state and corner case management
+ * @uaddr: the user address of the futex
+ * @fshared: whether the futex is shared (1) or not (0)
+ * @q: the futex_q (containes pi_state and access to the rt_mutex)
+ * @ret: the return value of the preceeding attempt to take the rt_mutex
+ *
+ * After attempting to take an rtmutex, process the return code and cleanup
+ * the pi_state as well as handle race conditions that may have caused us to
+ * lose the lock. Must be called with the hb lock held.
+ *
+ * Returns 0 on success, negative error code otherwise.
+ */
+static int finish_futex_lock_pi(u32 __user *uaddr, int fshared,
+ struct futex_q *q, int ret)
+{
+ if (!ret) {
+ /*
+ * Got the lock. We might not be the anticipated owner
+ * if we did a lock-steal - fix up the PI-state in
+ * that case:
+ */
+ if (q->pi_state->owner != current)
+ ret = fixup_pi_state_owner(uaddr, q, current, fshared);
+ return ret;
+ }
+
+ /*
+ * Catch the rare case, where the lock was released when we were on the
+ * way back before we locked the hash bucket.
+ */
+ if (q->pi_state->owner == current) {
+ /*
+ * Try to get the rt_mutex now. This might fail as some other
+ * task acquired the rt_mutex after we removed ourself from the
+ * rt_mutex waiters list.
+ */
+ if (rt_mutex_trylock(&q->pi_state->pi_mutex))
+ ret = 0;
+ else {
+ /*
+ * pi_state is incorrect, some other task did a lock
+ * steal and we returned due to timeout or signal
+ * without taking the rt_mutex. Too late. We can access
+ * the rt_mutex_owner without locking, as the other
+ * task is now blocked on the hash bucket lock. Fix the
+ * state up.
+ */
+ struct task_struct *owner;
+ int res;
+
+ owner = rt_mutex_owner(&q->pi_state->pi_mutex);
+ res = fixup_pi_state_owner(uaddr, q, owner,
+ fshared);
+
+ /* propagate -EFAULT, if the fixup failed */
+ if (res)
+ ret = res;
+ }
+ } else {
+ /* dvhart FIXME: can't we just BUG_ON in this case?
+ * Paranoia check. If we did not take the lock in the trylock
+ * above, then we should not be the owner of the rtmutex,
+ * neither the real nor the pending one:
+ */
+ if (rt_mutex_owner(&q->pi_state->pi_mutex) == current)
+ printk(KERN_ERR "finish_futex_lock_pi: "
+ "ret = %d pi-mutex: %p "
+ "pi-state %p\n", ret,
+ q->pi_state->pi_mutex.owner,
+ q->pi_state->owner);
+ }
+
+ return ret != -EINTR ? ret : -ERESTARTNOINTR;
+}
+
/*
* futex_wait_queue_me - queue_me and wait for wakeup, timeout, or signal.
* @hb: the futex hash bucket, must be locked by the caller
@@ -1505,7 +1580,6 @@ static int futex_lock_pi(u32 __user *uaddr, int fshared,
int detect, ktime_t *time, int trylock)
{
struct hrtimer_sleeper timeout, *to = NULL;
- struct task_struct *curr = current;
struct futex_hash_bucket *hb;
u32 uval;
struct futex_q q;
@@ -1572,74 +1646,12 @@ retry_unlocked:
}
spin_lock(q.lock_ptr);
-
- if (!ret) {
- /*
- * Got the lock. We might not be the anticipated owner
- * if we did a lock-steal - fix up the PI-state in
- * that case:
- */
- if (q.pi_state->owner != curr)
- ret = fixup_pi_state_owner(uaddr, &q, curr, fshared);
- } else {
- /*
- * Catch the rare case, where the lock was released
- * when we were on the way back before we locked the
- * hash bucket.
- */
- if (q.pi_state->owner == curr) {
- /*
- * Try to get the rt_mutex now. This might
- * fail as some other task acquired the
- * rt_mutex after we removed ourself from the
- * rt_mutex waiters list.
- */
- if (rt_mutex_trylock(&q.pi_state->pi_mutex))
- ret = 0;
- else {
- /*
- * pi_state is incorrect, some other
- * task did a lock steal and we
- * returned due to timeout or signal
- * without taking the rt_mutex. Too
- * late. We can access the
- * rt_mutex_owner without locking, as
- * the other task is now blocked on
- * the hash bucket lock. Fix the state
- * up.
- */
- struct task_struct *owner;
- int res;
-
- owner = rt_mutex_owner(&q.pi_state->pi_mutex);
- res = fixup_pi_state_owner(uaddr, &q, owner,
- fshared);
-
- /* propagate -EFAULT, if the fixup failed */
- if (res)
- ret = res;
- }
- } else {
- /*
- * Paranoia check. If we did not take the lock
- * in the trylock above, then we should not be
- * the owner of the rtmutex, neither the real
- * nor the pending one:
- */
- if (rt_mutex_owner(&q.pi_state->pi_mutex) == curr)
- printk(KERN_ERR "futex_lock_pi: ret = %d "
- "pi-mutex: %p pi-state %p\n", ret,
- q.pi_state->pi_mutex.owner,
- q.pi_state->owner);
- }
- }
+ ret = finish_futex_lock_pi(uaddr, fshared, &q, ret);
/* Unqueue and drop the lock */
unqueue_me_pi(&q);
- if (to)
- destroy_hrtimer_on_stack(&to->timer);
- return ret != -EINTR ? ret : -ERESTARTNOINTR;
+ goto out;
out_unlock_put_key:
queue_unlock(&q, hb);
@@ -1672,9 +1684,7 @@ uaddr_faulted:
if (!ret)
goto retry;
- if (to)
- destroy_hrtimer_on_stack(&to->timer);
- return ret;
+ goto out;
}
/*
--
Darren Hart
IBM Linux Technology Center
Real-Time Linux Team
--
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