This is a note to let you know that I've just added the patch titled sched/core: Fix reset-on-fork from RT with uclamp to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: sched-core-fix-reset-on-fork-from-rt-with-uclamp.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From eaf5a92ebde5bca3bb2565616115bd6d579486cd Mon Sep 17 00:00:00 2001 From: Quentin Perret <qperret@xxxxxxxxxx> Date: Thu, 16 Apr 2020 09:59:56 +0100 Subject: sched/core: Fix reset-on-fork from RT with uclamp From: Quentin Perret <qperret@xxxxxxxxxx> commit eaf5a92ebde5bca3bb2565616115bd6d579486cd upstream. uclamp_fork() resets the uclamp values to their default when the reset-on-fork flag is set. It also checks whether the task has a RT policy, and sets its uclamp.min to 1024 accordingly. However, during reset-on-fork, the task's policy is lowered to SCHED_NORMAL right after, hence leading to an erroneous uclamp.min setting for the new task if it was forked from RT. Fix this by removing the unnecessary check on rt_task() in uclamp_fork() as this doesn't make sense if the reset-on-fork flag is set. Fixes: 1a00d999971c ("sched/uclamp: Set default clamps for RT tasks") Reported-by: Chitti Babu Theegala <ctheegal@xxxxxxxxxxxxxx> Signed-off-by: Quentin Perret <qperret@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Reviewed-by: Patrick Bellasi <patrick.bellasi@xxxxxxxxxx> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@xxxxxxx> Link: https://lkml.kernel.org/r/20200416085956.217587-1-qperret@xxxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/sched/core.c | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1233,13 +1233,8 @@ static void uclamp_fork(struct task_stru return; for_each_clamp_id(clamp_id) { - unsigned int clamp_value = uclamp_none(clamp_id); - - /* By default, RT tasks always get 100% boost */ - if (unlikely(rt_task(p) && clamp_id == UCLAMP_MIN)) - clamp_value = uclamp_none(UCLAMP_MAX); - - uclamp_se_set(&p->uclamp_req[clamp_id], clamp_value, false); + uclamp_se_set(&p->uclamp_req[clamp_id], + uclamp_none(clamp_id), false); } } Patches currently in stable-queue which might be from qperret@xxxxxxxxxx are queue-5.4/sched-core-fix-reset-on-fork-from-rt-with-uclamp.patch