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authorLinus Torvalds <torvalds@linux-foundation.org>2021-05-09 13:14:34 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-05-09 13:14:34 -0700
commit9819f682e48c6a7055c5d7a6746411dd3969b0e5 (patch)
tree12abb30d0ecb449416299c4579755e8ffc1765b3
parent732a27a0891cb5db1a0f9c33a018ea6eca9a4023 (diff)
parent0258bdfaff5bd13c4d2383150b7097aecd6b6d82 (diff)
downloadandroid-dev-9819f682e48c6a7055c5d7a6746411dd3969b0e5.tar.gz
Merge tag 'sched-urgent-2021-05-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler fixes from Thomas Gleixner: "A set of scheduler updates: - Prevent PSI state corruption when schedule() races with cgroup move. A recent commit combined two PSI callbacks to reduce the number of cgroup tree updates, but missed that schedule() can drop rq::lock for load balancing, which opens the race window for cgroup_move_task() which then observes half updated state. The fix is to solely use task::ps_flags instead of looking at the potentially mismatching scheduler state - Prevent an out-of-bounds access in uclamp caused bu a rounding division which can lead to an off-by-one error exceeding the buckets array size. - Prevent unfairness caused by missing load decay when a task is attached to a cfs runqueue. The old load of the task was attached to the runqueue and never removed. Fix it by enforcing the load update through the hierarchy for unthrottled run queue instances. - A documentation fix fot the 'sched_verbose' command line option" * tag 'sched-urgent-2021-05-09' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: sched/fair: Fix unfairness caused by missing load decay sched: Fix out-of-bound access in uclamp psi: Fix psi state corruption when schedule() races with cgroup move sched,doc: sched_debug_verbose cmdline should be sched_verbose
-rw-r--r--Documentation/scheduler/sched-domains.rst2
-rw-r--r--kernel/sched/core.c2
-rw-r--r--kernel/sched/fair.c12
-rw-r--r--kernel/sched/psi.c36
4 files changed, 37 insertions, 15 deletions
diff --git a/Documentation/scheduler/sched-domains.rst b/Documentation/scheduler/sched-domains.rst
index 14ea2f21d20e..84dcdcd2911c 100644
--- a/Documentation/scheduler/sched-domains.rst
+++ b/Documentation/scheduler/sched-domains.rst
@@ -74,7 +74,7 @@ for a given topology level by creating a sched_domain_topology_level array and
calling set_sched_topology() with this array as the parameter.
The sched-domains debugging infrastructure can be enabled by enabling
-CONFIG_SCHED_DEBUG and adding 'sched_debug_verbose' to your cmdline. If you
+CONFIG_SCHED_DEBUG and adding 'sched_verbose' to your cmdline. If you
forgot to tweak your cmdline, you can also flip the
/sys/kernel/debug/sched/verbose knob. This enables an error checking parse of
the sched domains which should catch most possible errors (described above). It
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9143163fa678..5226cc26a095 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -938,7 +938,7 @@ DEFINE_STATIC_KEY_FALSE(sched_uclamp_used);
static inline unsigned int uclamp_bucket_id(unsigned int clamp_value)
{
- return clamp_value / UCLAMP_BUCKET_DELTA;
+ return min_t(unsigned int, clamp_value / UCLAMP_BUCKET_DELTA, UCLAMP_BUCKETS - 1);
}
static inline unsigned int uclamp_none(enum uclamp_id clamp_id)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 1d75af1ecfb4..20aa234ffe04 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10878,16 +10878,22 @@ static void propagate_entity_cfs_rq(struct sched_entity *se)
{
struct cfs_rq *cfs_rq;
+ list_add_leaf_cfs_rq(cfs_rq_of(se));
+
/* Start to propagate at parent */
se = se->parent;
for_each_sched_entity(se) {
cfs_rq = cfs_rq_of(se);
- if (cfs_rq_throttled(cfs_rq))
- break;
+ if (!cfs_rq_throttled(cfs_rq)){
+ update_load_avg(cfs_rq, se, UPDATE_TG);
+ list_add_leaf_cfs_rq(cfs_rq);
+ continue;
+ }
- update_load_avg(cfs_rq, se, UPDATE_TG);
+ if (list_add_leaf_cfs_rq(cfs_rq))
+ break;
}
}
#else
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index db27b69fa92a..cc25a3cff41f 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -972,7 +972,7 @@ void psi_cgroup_free(struct cgroup *cgroup)
*/
void cgroup_move_task(struct task_struct *task, struct css_set *to)
{
- unsigned int task_flags = 0;
+ unsigned int task_flags;
struct rq_flags rf;
struct rq *rq;
@@ -987,15 +987,31 @@ void cgroup_move_task(struct task_struct *task, struct css_set *to)
rq = task_rq_lock(task, &rf);
- if (task_on_rq_queued(task)) {
- task_flags = TSK_RUNNING;
- if (task_current(rq, task))
- task_flags |= TSK_ONCPU;
- } else if (task->in_iowait)
- task_flags = TSK_IOWAIT;
-
- if (task->in_memstall)
- task_flags |= TSK_MEMSTALL;
+ /*
+ * We may race with schedule() dropping the rq lock between
+ * deactivating prev and switching to next. Because the psi
+ * updates from the deactivation are deferred to the switch
+ * callback to save cgroup tree updates, the task's scheduling
+ * state here is not coherent with its psi state:
+ *
+ * schedule() cgroup_move_task()
+ * rq_lock()
+ * deactivate_task()
+ * p->on_rq = 0
+ * psi_dequeue() // defers TSK_RUNNING & TSK_IOWAIT updates
+ * pick_next_task()
+ * rq_unlock()
+ * rq_lock()
+ * psi_task_change() // old cgroup
+ * task->cgroups = to
+ * psi_task_change() // new cgroup
+ * rq_unlock()
+ * rq_lock()
+ * psi_sched_switch() // does deferred updates in new cgroup
+ *
+ * Don't rely on the scheduling state. Use psi_flags instead.
+ */
+ task_flags = task->psi_flags;
if (task_flags)
psi_task_change(task, task_flags, 0);