On Thu, 2021-02-04 at 17:28 +0000, Lee Jones wrote:
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
kernel/futex.c | 64 ++++++++++++++++++++++++++----------------------
1 file changed, 33 insertions(+), 31 deletions(-)
diff --git a/kernel/futex.c b/kernel/futex.c index a247942d69799..1390ffa874a6b 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -835,6 +835,29 @@ 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);
But not all callers do hold the wait_lock. That may not be needed as we don't have commit 734009e96d19 "futex: Change locking rules".
+ if (old_owner) { + raw_spin_lock(&old_owner->pi_lock);
(Some of) the callers used to disable interrupts when taking pi_lock, and I think that behaviour needs to be preserved here.
I'm doubtful that this cherry-picking approach is going to work.
Ben.
+ 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 *uaddr, u32 uval, struct futex_q *this, 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; /*