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authorPeter Zijlstra <peterz@infradead.org>2017-03-23 15:56:13 +0100
committerThomas Gleixner <tglx@linutronix.de>2017-04-04 11:44:06 +0200
commite0aad5b44ff5d28ac1d6ae70cdf84ca228e889dc (patch)
tree5e15c53d3b2fa6096e14073a3f0140ca81aeeda4 /kernel/locking
parentb91473ff6e979c0028f02f90e40c844959c736d8 (diff)
downloadlinux-e0aad5b44ff5d28ac1d6ae70cdf84ca228e889dc.tar.bz2
rtmutex: Fix PI chain order integrity
rt_mutex_waiter::prio is a copy of task_struct::prio which is updated during the PI chain walk, such that the PI chain order isn't messed up by (asynchronous) task state updates. Currently rt_mutex_waiter_less() uses task state for deadline tasks; this is broken, since the task state can, as said above, change asynchronously, causing the RB tree order to change without actual tree update -> FAIL. Fix this by also copying the deadline into the rt_mutex_waiter state and updating it along with its prio field. Ideally we would also force PI chain updates whenever DL tasks update their deadline parameter, but for first approximation this is less broken than it was. 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: bristot@redhat.com Link: http://lkml.kernel.org/r/20170323150216.403992539@infradead.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'kernel/locking')
-rw-r--r--kernel/locking/rtmutex.c29
-rw-r--r--kernel/locking/rtmutex_common.h1
2 files changed, 28 insertions, 2 deletions
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 00b49cdbb4e0..c6eda049ef9f 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -238,8 +238,7 @@ rt_mutex_waiter_less(struct rt_mutex_waiter *left,
* then right waiter has a dl_prio() too.
*/
if (dl_prio(left->prio))
- return dl_time_before(left->task->dl.deadline,
- right->task->dl.deadline);
+ return dl_time_before(left->deadline, right->deadline);
return 0;
}
@@ -650,7 +649,26 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
/* [7] Requeue the waiter in the lock waiter tree. */
rt_mutex_dequeue(lock, waiter);
+
+ /*
+ * Update the waiter prio fields now that we're dequeued.
+ *
+ * These values can have changed through either:
+ *
+ * sys_sched_set_scheduler() / sys_sched_setattr()
+ *
+ * or
+ *
+ * DL CBS enforcement advancing the effective deadline.
+ *
+ * Even though pi_waiters also uses these fields, and that tree is only
+ * updated in [11], we can do this here, since we hold [L], which
+ * serializes all pi_waiters access and rb_erase() does not care about
+ * the values of the node being removed.
+ */
waiter->prio = task->prio;
+ waiter->deadline = task->dl.deadline;
+
rt_mutex_enqueue(lock, waiter);
/* [8] Release the task */
@@ -777,6 +795,8 @@ static int rt_mutex_adjust_prio_chain(struct task_struct *task,
static int try_to_take_rt_mutex(struct rt_mutex *lock, struct task_struct *task,
struct rt_mutex_waiter *waiter)
{
+ lockdep_assert_held(&lock->wait_lock);
+
/*
* Before testing whether we can acquire @lock, we set the
* RT_MUTEX_HAS_WAITERS bit in @lock->owner. This forces all
@@ -902,6 +922,8 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
struct rt_mutex *next_lock;
int chain_walk = 0, res;
+ lockdep_assert_held(&lock->wait_lock);
+
/*
* Early deadlock detection. We really don't want the task to
* enqueue on itself just to untangle the mess later. It's not
@@ -919,6 +941,7 @@ static int task_blocks_on_rt_mutex(struct rt_mutex *lock,
waiter->task = task;
waiter->lock = lock;
waiter->prio = task->prio;
+ waiter->deadline = task->dl.deadline;
/* Get the top priority waiter on the lock */
if (rt_mutex_has_waiters(lock))
@@ -1036,6 +1059,8 @@ static void remove_waiter(struct rt_mutex *lock,
struct task_struct *owner = rt_mutex_owner(lock);
struct rt_mutex *next_lock;
+ lockdep_assert_held(&lock->wait_lock);
+
raw_spin_lock(&current->pi_lock);
rt_mutex_dequeue(lock, waiter);
current->pi_blocked_on = NULL;
diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
index 9e36aeddce18..72ad45a9a794 100644
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -34,6 +34,7 @@ struct rt_mutex_waiter {
struct rt_mutex *deadlock_lock;
#endif
int prio;
+ u64 deadline;
};
/*