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authorIngo Molnar <mingo@kernel.org>2016-12-02 11:13:44 +0100
committerIngo Molnar <mingo@kernel.org>2016-12-02 11:13:44 +0100
commit1b95b1a06cb27badb3e53329fb56af2a2113fd80 (patch)
treebbe52b10fde003833c980b0a30dd23b0e0855c87 /kernel
parent3cded41794818d788aa1dc028ede4a1c1222d937 (diff)
parent1be5d4fa0af34fb7bafa205aeb59f5c7cc7a089d (diff)
Merge branch 'locking/urgent' into locking/core, to pick up dependent fixes
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/events/core.c13
-rw-r--r--kernel/exit.c1
-rw-r--r--kernel/locking/rtmutex.c68
-rw-r--r--kernel/locking/rtmutex_common.h5
-rw-r--r--kernel/sched/auto_group.c36
5 files changed, 111 insertions, 12 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 0e292132efac..6ee1febdf6ff 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -902,6 +902,17 @@ list_update_cgroup_event(struct perf_event *event,
* this will always be called from the right CPU.
*/
cpuctx = __get_cpu_context(ctx);
+
+ /* Only set/clear cpuctx->cgrp if current task uses event->cgrp. */
+ if (perf_cgroup_from_task(current, ctx) != event->cgrp) {
+ /*
+ * We are removing the last cpu event in this context.
+ * If that event is not active in this cpu, cpuctx->cgrp
+ * should've been cleared by perf_cgroup_switch.
+ */
+ WARN_ON_ONCE(!add && cpuctx->cgrp);
+ return;
+ }
cpuctx->cgrp = add ? event->cgrp : NULL;
}
@@ -8018,6 +8029,7 @@ restart:
* if <size> is not specified, the range is treated as a single address.
*/
enum {
+ IF_ACT_NONE = -1,
IF_ACT_FILTER,
IF_ACT_START,
IF_ACT_STOP,
@@ -8041,6 +8053,7 @@ static const match_table_t if_tokens = {
{ IF_SRC_KERNEL, "%u/%u" },
{ IF_SRC_FILEADDR, "%u@%s" },
{ IF_SRC_KERNELADDR, "%u" },
+ { IF_ACT_NONE, NULL },
};
/*
diff --git a/kernel/exit.c b/kernel/exit.c
index 9d68c45ebbe3..3076f3089919 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -836,6 +836,7 @@ void __noreturn do_exit(long code)
*/
perf_event_exit_task(tsk);
+ sched_autogroup_exit_task(tsk);
cgroup_exit(tsk);
/*
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index d8d7a153b711..6e6cab7ac12f 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -65,8 +65,72 @@ static inline void clear_rt_mutex_waiters(struct rt_mutex *lock)
static void fixup_rt_mutex_waiters(struct rt_mutex *lock)
{
- if (!rt_mutex_has_waiters(lock))
- clear_rt_mutex_waiters(lock);
+ unsigned long owner, *p = (unsigned long *) &lock->owner;
+
+ if (rt_mutex_has_waiters(lock))
+ return;
+
+ /*
+ * The rbtree has no waiters enqueued, now make sure that the
+ * lock->owner still has the waiters bit set, otherwise the
+ * following can happen:
+ *
+ * CPU 0 CPU 1 CPU2
+ * l->owner=T1
+ * rt_mutex_lock(l)
+ * lock(l->lock)
+ * l->owner = T1 | HAS_WAITERS;
+ * enqueue(T2)
+ * boost()
+ * unlock(l->lock)
+ * block()
+ *
+ * rt_mutex_lock(l)
+ * lock(l->lock)
+ * l->owner = T1 | HAS_WAITERS;
+ * enqueue(T3)
+ * boost()
+ * unlock(l->lock)
+ * block()
+ * signal(->T2) signal(->T3)
+ * lock(l->lock)
+ * dequeue(T2)
+ * deboost()
+ * unlock(l->lock)
+ * lock(l->lock)
+ * dequeue(T3)
+ * ==> wait list is empty
+ * deboost()
+ * unlock(l->lock)
+ * lock(l->lock)
+ * fixup_rt_mutex_waiters()
+ * if (wait_list_empty(l) {
+ * l->owner = owner
+ * owner = l->owner & ~HAS_WAITERS;
+ * ==> l->owner = T1
+ * }
+ * lock(l->lock)
+ * rt_mutex_unlock(l) fixup_rt_mutex_waiters()
+ * if (wait_list_empty(l) {
+ * owner = l->owner & ~HAS_WAITERS;
+ * cmpxchg(l->owner, T1, NULL)
+ * ===> Success (l->owner = NULL)
+ *
+ * l->owner = owner
+ * ==> l->owner = T1
+ * }
+ *
+ * With the check for the waiter bit in place T3 on CPU2 will not
+ * overwrite. All tasks fiddling with the waiters bit are
+ * serialized by l->lock, so nothing else can modify the waiters
+ * bit. If the bit is set then nothing can change l->owner either
+ * so the simple RMW is safe. The cmpxchg() will simply fail if it
+ * happens in the middle of the RMW because the waiters bit is
+ * still set.
+ */
+ owner = READ_ONCE(*p);
+ if (owner & RT_MUTEX_HAS_WAITERS)
+ WRITE_ONCE(*p, owner & ~RT_MUTEX_HAS_WAITERS);
}
/*
diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
index 4f5f83c7d2d3..e317e1cbb3eb 100644
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -75,8 +75,9 @@ task_top_pi_waiter(struct task_struct *p)
static inline struct task_struct *rt_mutex_owner(struct rt_mutex *lock)
{
- return (struct task_struct *)
- ((unsigned long)lock->owner & ~RT_MUTEX_OWNER_MASKALL);
+ unsigned long owner = (unsigned long) READ_ONCE(lock->owner);
+
+ return (struct task_struct *) (owner & ~RT_MUTEX_OWNER_MASKALL);
}
/*
diff --git a/kernel/sched/auto_group.c b/kernel/sched/auto_group.c
index a5d966cb8891..f1c8fd566246 100644
--- a/kernel/sched/auto_group.c
+++ b/kernel/sched/auto_group.c
@@ -111,10 +111,13 @@ bool task_wants_autogroup(struct task_struct *p, struct task_group *tg)
{
if (tg != &root_task_group)
return false;
-
/*
- * We can only assume the task group can't go away on us if
- * autogroup_move_group() can see us on ->thread_group list.
+ * If we race with autogroup_move_group() the caller can use the old
+ * value of signal->autogroup but in this case sched_move_task() will
+ * be called again before autogroup_kref_put().
+ *
+ * However, there is no way sched_autogroup_exit_task() could tell us
+ * to avoid autogroup->tg, so we abuse PF_EXITING flag for this case.
*/
if (p->flags & PF_EXITING)
return false;
@@ -122,6 +125,16 @@ bool task_wants_autogroup(struct task_struct *p, struct task_group *tg)
return true;
}
+void sched_autogroup_exit_task(struct task_struct *p)
+{
+ /*
+ * We are going to call exit_notify() and autogroup_move_group() can't
+ * see this thread after that: we can no longer use signal->autogroup.
+ * See the PF_EXITING check in task_wants_autogroup().
+ */
+ sched_move_task(p);
+}
+
static void
autogroup_move_group(struct task_struct *p, struct autogroup *ag)
{
@@ -138,13 +151,20 @@ autogroup_move_group(struct task_struct *p, struct autogroup *ag)
}
p->signal->autogroup = autogroup_kref_get(ag);
-
- if (!READ_ONCE(sysctl_sched_autogroup_enabled))
- goto out;
-
+ /*
+ * We can't avoid sched_move_task() after we changed signal->autogroup,
+ * this process can already run with task_group() == prev->tg or we can
+ * race with cgroup code which can read autogroup = prev under rq->lock.
+ * In the latter case for_each_thread() can not miss a migrating thread,
+ * cpu_cgroup_attach() must not be possible after cgroup_exit() and it
+ * can't be removed from thread list, we hold ->siglock.
+ *
+ * If an exiting thread was already removed from thread list we rely on
+ * sched_autogroup_exit_task().
+ */
for_each_thread(p, t)
sched_move_task(t);
-out:
+
unlock_task_sighand(p, &flags);
autogroup_kref_put(prev);
}