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authorQais Yousef <qais.yousef@arm.com>2020-07-16 12:03:47 +0100
committerPeter Zijlstra <peterz@infradead.org>2020-07-29 13:51:47 +0200
commite65855a52b479f98674998cb23b21ef5a8144b04 (patch)
treeea641813091126bbc0d7ef4ec02b938cbe8488d8 /kernel/sched
parent21a6ee14a8f277766618ef07154432b46528113e (diff)
sched/uclamp: Fix a deadlock when enabling uclamp static key
The following splat was caught when setting uclamp value of a task: BUG: sleeping function called from invalid context at ./include/linux/percpu-rwsem.h:49 cpus_read_lock+0x68/0x130 static_key_enable+0x1c/0x38 __sched_setscheduler+0x900/0xad8 Fix by ensuring we enable the key outside of the critical section in __sched_setscheduler() Fixes: 46609ce22703 ("sched/uclamp: Protect uclamp fast path code with static key") Signed-off-by: Qais Yousef <qais.yousef@arm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lkml.kernel.org/r/20200716110347.19553-4-qais.yousef@arm.com
Diffstat (limited to 'kernel/sched')
-rw-r--r--kernel/sched/core.c11
1 files changed, 9 insertions, 2 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 678253450ebb..e44d83f3e0e6 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1346,6 +1346,15 @@ static int uclamp_validate(struct task_struct *p,
if (upper_bound > SCHED_CAPACITY_SCALE)
return -EINVAL;
+ /*
+ * We have valid uclamp attributes; make sure uclamp is enabled.
+ *
+ * We need to do that here, because enabling static branches is a
+ * blocking operation which obviously cannot be done while holding
+ * scheduler locks.
+ */
+ static_branch_enable(&sched_uclamp_used);
+
return 0;
}
@@ -1376,8 +1385,6 @@ static void __setscheduler_uclamp(struct task_struct *p,
if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP)))
return;
- static_branch_enable(&sched_uclamp_used);
-
if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) {
uclamp_se_set(&p->uclamp_req[UCLAMP_MIN],
attr->sched_util_min, true);