[PATCH 4.4 07/38] futex: Provide and use pi_state_update_owner()

Greg Kroah-Hartman
2021-02-08T15:11:01Z

From: Lee Jones <lee.jones@linaro.org>

From: Thomas Gleixner <tglx@linutronix.de>

[ Upstream commit c5cade200ab9a2a3be9e7f32a752c8d86b502ec7 ]

Updating pi_state::owner is done at several places with the same
code. Provide a function for it and use that at the obvious places.

This is also a preparation for a bug fix to avoid yet another copy of the
same code or alternatively introducing a completely unpenetratable mess of
gotos.

Originally-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: stable@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/futex.c | 64 +++++++++++++++++++++++++++++----------------------------
1 file changed, 33 insertions(+), 31 deletions(-)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -835,6 +835,29 @@ static struct futex_pi_state * alloc_pi_
return pi_state;
}

+static void pi_state_update_owner(struct futex_pi_state *pi_state,
+ struct task_struct *new_owner)
+{
+ struct task_struct *old_owner = pi_state->owner;
+
+ lockdep_assert_held(&pi_state->pi_mutex.wait_lock);
+
+ if (old_owner) {
+ raw_spin_lock(&old_owner->pi_lock);
+ WARN_ON(list_empty(&pi_state->list));
+ list_del_init(&pi_state->list);
+ raw_spin_unlock(&old_owner->pi_lock);
+ }
+
+ if (new_owner) {
+ raw_spin_lock(&new_owner->pi_lock);
+ WARN_ON(!list_empty(&pi_state->list));
+ list_add(&pi_state->list, &new_owner->pi_state_list);
+ pi_state->owner = new_owner;
+ raw_spin_unlock(&new_owner->pi_lock);
+ }
+}
+
/*
* Must be called with the hb lock held.
*/
@@ -1427,26 +1450,16 @@ static int wake_futex_pi(u32 __user *uad
else
ret = -EINVAL;
}
- if (ret) {
- raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
- return ret;
- }
-
- raw_spin_lock_irq(&pi_state->owner->pi_lock);
- WARN_ON(list_empty(&pi_state->list));
- list_del_init(&pi_state->list);
- raw_spin_unlock_irq(&pi_state->owner->pi_lock);

- raw_spin_lock_irq(&new_owner->pi_lock);
- WARN_ON(!list_empty(&pi_state->list));
- list_add(&pi_state->list, &new_owner->pi_state_list);
- pi_state->owner = new_owner;
- raw_spin_unlock_irq(&new_owner->pi_lock);
-
- /*
- * We've updated the uservalue, this unlock cannot fail.
- */
- deboost = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
+ if (!ret) {
+ /*
+ * This is a point of no return; once we modified the uval
+ * there is no going back and subsequent operations must
+ * not fail.
+ */
+ pi_state_update_owner(pi_state, new_owner);
+ deboost = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
+ }

raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
spin_unlock(&hb->lock);
@@ -2318,19 +2331,8 @@ retry:
* We fixed up user space. Now we need to fix the pi_state
* itself.
*/
- if (pi_state->owner != NULL) {
- raw_spin_lock_irq(&pi_state->owner->pi_lock);
- WARN_ON(list_empty(&pi_state->list));
- list_del_init(&pi_state->list);
- raw_spin_unlock_irq(&pi_state->owner->pi_lock);
- }
-
- pi_state->owner = newowner;
+ pi_state_update_owner(pi_state, newowner);

- raw_spin_lock_irq(&newowner->pi_lock);
- WARN_ON(!list_empty(&pi_state->list));
- list_add(&pi_state->list, &newowner->pi_state_list);
- raw_spin_unlock_irq(&newowner->pi_lock);
return 0;

/*