[PATCH 4.4 02/11] futex: Cleanup refcounting

Greg Kroah-Hartman
2021-08-08T07:23:10Z

From: Peter Zijlstra <peterz@infradead.org>

[ Upstream commit bf92cf3a5100f5a0d5f9834787b130159397cb22 ]

Add a put_pit_state() as counterpart for get_pi_state() so the refcounting
becomes consistent.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104151.801778516@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Acked-by: Joe Korty <joe.korty@concurrent-rt.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/futex.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -825,7 +825,7 @@ 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;

@@ -858,6 +858,11 @@ static void pi_state_update_owner(struct
}
}

+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.
@@ -901,7 +906,7 @@ 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;

@@ -1149,7 +1154,7 @@ 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;
@@ -2204,7 +2209,7 @@ retry_private:
*/
if (requeue_pi) {
/* Prepare the waiter to take the rt_mutex. */
- 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,