[PATCH -v5 08/14] futex: Cleanup refcounting

From: Peter Zijlstra
Date: Sat Mar 04 2017 - 06:44:35 EST


Since we're going to add more refcount fiddling, introduce
get_pi_state() to match the existing put_pi_state().

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
kernel/futex.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -802,7 +802,7 @@ static int refill_pi_state_cache(void)
return 0;
}

-static struct futex_pi_state * alloc_pi_state(void)
+static struct futex_pi_state *alloc_pi_state(void)
{
struct futex_pi_state *pi_state = current->pi_state_cache;

@@ -812,6 +812,11 @@ static struct futex_pi_state * alloc_pi_
return pi_state;
}

+static void get_pi_state(struct futex_pi_state *pi_state)
+{
+ WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount));
+}
+
/*
* Drops a reference to the pi_state object and frees or caches it
* when the last reference is gone.
@@ -856,7 +861,7 @@ static void put_pi_state(struct futex_pi
* Look up the task based on what TID userspace gave us.
* We dont trust it.
*/
-static struct task_struct * futex_find_get_task(pid_t pid)
+static struct task_struct *futex_find_get_task(pid_t pid)
{
struct task_struct *p;

@@ -1103,7 +1108,7 @@ static int attach_to_pi_state(u32 __user
goto out_einval;

out_attach:
- atomic_inc(&pi_state->refcount);
+ get_pi_state(pi_state);
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
*ps = pi_state;
return 0;
@@ -1990,7 +1995,7 @@ static int futex_requeue(u32 __user *uad
* refcount on the pi_state and store the pointer in
* the futex_q object of the waiter.
*/
- atomic_inc(&pi_state->refcount);
+ get_pi_state(pi_state);
this->pi_state = pi_state;
ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
this->rt_waiter,