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Subject[tip: locking/urgent] futex: Provide and use pi_state_update_owner()
The following commit has been merged into the locking/urgent branch of tip:

Commit-ID: c5cade200ab9a2a3be9e7f32a752c8d86b502ec7
Gitweb: https://git.kernel.org/tip/c5cade200ab9a2a3be9e7f32a752c8d86b502ec7
Author: Thomas Gleixner <tglx@linutronix.de>
AuthorDate: Tue, 19 Jan 2021 15:21:35 +01:00
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitterDate: Tue, 26 Jan 2021 15:10:58 +01:00

futex: Provide and use pi_state_update_owner()

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
---
kernel/futex.c | 66 ++++++++++++++++++++++++-------------------------
1 file changed, 33 insertions(+), 33 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index 5dc8f89..7837f9e 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -763,6 +763,29 @@ static struct futex_pi_state *alloc_pi_state(void)
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);
+ }
+}
+
static void get_pi_state(struct futex_pi_state *pi_state)
{
WARN_ON_ONCE(!refcount_inc_not_zero(&pi_state->refcount));
@@ -1521,26 +1544,15 @@ static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_
ret = -EINVAL;
}

- if (ret)
- goto out_unlock;
-
- /*
- * This is a point of no return; once we modify the uval there is no
- * going back and subsequent operations must not fail.
- */
-
- raw_spin_lock(&pi_state->owner->pi_lock);
- WARN_ON(list_empty(&pi_state->list));
- list_del_init(&pi_state->list);
- raw_spin_unlock(&pi_state->owner->pi_lock);
-
- 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);
-
- postunlock = __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);
+ postunlock = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
+ }

out_unlock:
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
@@ -2433,19 +2445,7 @@ retry:
* We fixed up user space. Now we need to fix the pi_state
* itself.
*/
- if (pi_state->owner != NULL) {
- raw_spin_lock(&pi_state->owner->pi_lock);
- WARN_ON(list_empty(&pi_state->list));
- list_del_init(&pi_state->list);
- raw_spin_unlock(&pi_state->owner->pi_lock);
- }
-
- pi_state->owner = newowner;
-
- raw_spin_lock(&newowner->pi_lock);
- WARN_ON(!list_empty(&pi_state->list));
- list_add(&pi_state->list, &newowner->pi_state_list);
- raw_spin_unlock(&newowner->pi_lock);
+ pi_state_update_owner(pi_state, newowner);
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);

return argowner == current;
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