Revert "futex: Prevent exit livelock"
This reverts commit 699fd21d4b0199b78523b8b66b4526eb8a8c13b0.
Change-Id: Idf49a57c650295709e778564e4114d86bd7de23c
diff --git a/kernel/futex.c b/kernel/futex.c
index 0acfc8ad..8f4c503 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -1194,36 +1194,6 @@
return ret;
}
-/**
- * wait_for_owner_exiting - Block until the owner has exited
- * @exiting: Pointer to the exiting task
- *
- * Caller must hold a refcount on @exiting.
- */
-static void wait_for_owner_exiting(int ret, struct task_struct *exiting)
-{
- if (ret != -EBUSY) {
- WARN_ON_ONCE(exiting);
- return;
- }
-
- if (WARN_ON_ONCE(ret == -EBUSY && !exiting))
- return;
-
- mutex_lock(&exiting->futex_exit_mutex);
- /*
- * No point in doing state checking here. If the waiter got here
- * while the task was in exec()->exec_futex_release() then it can
- * have any FUTEX_STATE_* value when the waiter has acquired the
- * mutex. OK, if running, EXITING or DEAD if it reached exit()
- * already. Highly unlikely and not a problem. Just one more round
- * through the futex maze.
- */
- mutex_unlock(&exiting->futex_exit_mutex);
-
- put_task_struct(exiting);
-}
-
static int handle_exit_race(u32 __user *uaddr, u32 uval,
struct task_struct *tsk)
{
@@ -1285,8 +1255,7 @@
* it after doing proper sanity checks.
*/
static int attach_to_pi_owner(u32 __user *uaddr, u32 uval, union futex_key *key,
- struct futex_pi_state **ps,
- struct task_struct **exiting)
+ struct futex_pi_state **ps)
{
pid_t pid = uval & FUTEX_TID_MASK;
struct futex_pi_state *pi_state;
@@ -1325,19 +1294,7 @@
int ret = handle_exit_race(uaddr, uval, p);
raw_spin_unlock_irq(&p->pi_lock);
- /*
- * If the owner task is between FUTEX_STATE_EXITING and
- * FUTEX_STATE_DEAD then store the task pointer and keep
- * the reference on the task struct. The calling code will
- * drop all locks, wait for the task to reach
- * FUTEX_STATE_DEAD and then drop the refcount. This is
- * required to prevent a live lock when the current task
- * preempted the exiting task between the two states.
- */
- if (ret == -EBUSY)
- *exiting = p;
- else
- put_task_struct(p);
+ put_task_struct(p);
return ret;
}
@@ -1376,8 +1333,7 @@
static int lookup_pi_state(u32 __user *uaddr, u32 uval,
struct futex_hash_bucket *hb,
- union futex_key *key, struct futex_pi_state **ps,
- struct task_struct **exiting)
+ union futex_key *key, struct futex_pi_state **ps)
{
struct futex_q *top_waiter = futex_top_waiter(hb, key);
@@ -1392,7 +1348,7 @@
* We are the first waiter - try to look up the owner based on
* @uval and attach to it.
*/
- return attach_to_pi_owner(uaddr, uval, key, ps, exiting);
+ return attach_to_pi_owner(uaddr, uval, key, ps);
}
static int lock_pi_update_atomic(u32 __user *uaddr, u32 uval, u32 newval)
@@ -1420,8 +1376,6 @@
* lookup
* @task: the task to perform the atomic lock work for. This will
* be "current" except in the case of requeue pi.
- * @exiting: Pointer to store the task pointer of the owner task
- * which is in the middle of exiting
* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
*
* Return:
@@ -1430,17 +1384,11 @@
* - <0 - error
*
* The hb->lock and futex_key refs shall be held by the caller.
- *
- * @exiting is only set when the return value is -EBUSY. If so, this holds
- * a refcount on the exiting task on return and the caller needs to drop it
- * after waiting for the exit to complete.
*/
static int futex_lock_pi_atomic(u32 __user *uaddr, struct futex_hash_bucket *hb,
union futex_key *key,
struct futex_pi_state **ps,
- struct task_struct *task,
- struct task_struct **exiting,
- int set_waiters)
+ struct task_struct *task, int set_waiters)
{
u32 uval, newval, vpid = task_pid_vnr(task);
struct futex_q *top_waiter;
@@ -1510,7 +1458,7 @@
* attach to the owner. If that fails, no harm done, we only
* set the FUTEX_WAITERS bit in the user space variable.
*/
- return attach_to_pi_owner(uaddr, newval, key, ps, exiting);
+ return attach_to_pi_owner(uaddr, newval, key, ps);
}
/**
@@ -1920,8 +1868,6 @@
* @key1: the from futex key
* @key2: the to futex key
* @ps: address to store the pi_state pointer
- * @exiting: Pointer to store the task pointer of the owner task
- * which is in the middle of exiting
* @set_waiters: force setting the FUTEX_WAITERS bit (1) or not (0)
*
* Try and get the lock on behalf of the top waiter if we can do it atomically.
@@ -1929,20 +1875,16 @@
* then direct futex_lock_pi_atomic() to force setting the FUTEX_WAITERS bit.
* hb1 and hb2 must be held by the caller.
*
- * @exiting is only set when the return value is -EBUSY. If so, this holds
- * a refcount on the exiting task on return and the caller needs to drop it
- * after waiting for the exit to complete.
- *
* Return:
* - 0 - failed to acquire the lock atomically;
* - >0 - acquired the lock, return value is vpid of the top_waiter
* - <0 - error
*/
-static int
-futex_proxy_trylock_atomic(u32 __user *pifutex, struct futex_hash_bucket *hb1,
- struct futex_hash_bucket *hb2, union futex_key *key1,
- union futex_key *key2, struct futex_pi_state **ps,
- struct task_struct **exiting, int set_waiters)
+static int futex_proxy_trylock_atomic(u32 __user *pifutex,
+ struct futex_hash_bucket *hb1,
+ struct futex_hash_bucket *hb2,
+ union futex_key *key1, union futex_key *key2,
+ struct futex_pi_state **ps, int set_waiters)
{
struct futex_q *top_waiter = NULL;
u32 curval;
@@ -1979,7 +1921,7 @@
*/
vpid = task_pid_vnr(top_waiter->task);
ret = futex_lock_pi_atomic(pifutex, hb2, key2, ps, top_waiter->task,
- exiting, set_waiters);
+ set_waiters);
if (ret == 1) {
requeue_pi_wake_futex(top_waiter, key2, hb2);
return vpid;
@@ -2108,8 +2050,6 @@
}
if (requeue_pi && (task_count - nr_wake < nr_requeue)) {
- struct task_struct *exiting = NULL;
-
/*
* Attempt to acquire uaddr2 and wake the top waiter. If we
* intend to requeue waiters, force setting the FUTEX_WAITERS
@@ -2117,8 +2057,7 @@
* faults rather in the requeue loop below.
*/
ret = futex_proxy_trylock_atomic(uaddr2, hb1, hb2, &key1,
- &key2, &pi_state,
- &exiting, nr_requeue);
+ &key2, &pi_state, nr_requeue);
/*
* At this point the top_waiter has either taken uaddr2 or is
@@ -2145,8 +2084,7 @@
* If that call succeeds then we have pi_state and an
* initial refcount on it.
*/
- ret = lookup_pi_state(uaddr2, ret, hb2, &key2,
- &pi_state, &exiting);
+ ret = lookup_pi_state(uaddr2, ret, hb2, &key2, &pi_state);
}
switch (ret) {
@@ -2176,12 +2114,6 @@
hb_waiters_dec(hb2);
put_futex_key(&key2);
put_futex_key(&key1);
- /*
- * Handle the case where the owner is in the middle of
- * exiting. Wait for the exit to complete otherwise
- * this task might loop forever, aka. live lock.
- */
- wait_for_owner_exiting(ret, exiting);
cond_resched();
goto retry;
default:
@@ -2904,7 +2836,6 @@
ktime_t *time, int trylock)
{
struct hrtimer_sleeper timeout, *to = NULL;
- struct task_struct *exiting = NULL;
struct rt_mutex_waiter rt_waiter;
struct futex_hash_bucket *hb;
struct futex_q q = futex_q_init;
@@ -2932,8 +2863,7 @@
retry_private:
hb = queue_lock(&q);
- ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current,
- &exiting, 0);
+ ret = futex_lock_pi_atomic(uaddr, hb, &q.key, &q.pi_state, current, 0);
if (unlikely(ret)) {
/*
* Atomic work succeeded and we got the lock,
@@ -2956,12 +2886,6 @@
*/
queue_unlock(hb);
put_futex_key(&q.key);
- /*
- * Handle the case where the owner is in the middle of
- * exiting. Wait for the exit to complete otherwise
- * this task might loop forever, aka. live lock.
- */
- wait_for_owner_exiting(ret, exiting);
cond_resched();
goto retry;
default:
