Commit 16187c3b authored Jul 16, 2020 by Qais Yousef Committed by Lee Jones Jan 17, 2024

UPSTREAM: 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()

Bug: 254441685
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


(cherry picked from commit e65855a52b479f98674998cb23b21ef5a8144b04)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I9b33882f72b2f5a8bb8a1e077e7785f3462d1cee

parent c188f80e

kernel/sched/core.c

+9 −2

Original line number	Diff line number	Diff line
		@@ -1217,6 +1217,15 @@ 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;
		}

		@@ -1251,8 +1260,6 @@ 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);