The patch below does not apply to the 4.19-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-4.19.y git checkout FETCH_HEAD git cherry-pick -x d329605287020c3d1c3b0dadc63d8208e7251382 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2024072951-crimson-ashamed-1d63@gregkh' --subject-prefix 'PATCH 4.19.y' HEAD^..

Possible dependencies:

d32960528702 ("sched/fair: set_load_weight() must also call reweight_task() for SCHED_IDLE tasks") 0dacee1bfa70 ("sched/pelt: Remove unused runnable load average") fe71bbb21ee1 ("sched/fair: calculate delta runnable load only when it's needed") 8de6242cca17 ("sched/debug: Add new tracepoint to track PELT at se level") ba19f51fcb54 ("sched/debug: Add new tracepoints to track PELT at rq level") 039ae8bcf7a5 ("sched/fair: Fix O(nr_cgroups) in the load balancing path") 5d299eabea5a ("sched/fair: Add tmp_alone_branch assertion") 23127296889f ("sched/fair: Update scale invariance of PELT") c40f7d74c741 ("sched/fair: Fix infinite loop in update_blocked_averages() by reverting a9e7f6544b9c") dfcb245e2848 ("sched: Fix various typos in comments") 1da1843f9f03 ("sched/core: Create task_has_idle_policy() helper") 4a465e3ebbc8 ("sched/fair: Remove setting task's se->runnable_weight during PELT update")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d329605287020c3d1c3b0dadc63d8208e7251382 Mon Sep 17 00:00:00 2001 From: Tejun Heo tj@kernel.org Date: Tue, 25 Jun 2024 15:29:58 -1000 Subject: [PATCH] sched/fair: set_load_weight() must also call reweight_task() for SCHED_IDLE tasks

When a task's weight is being changed, set_load_weight() is called with @update_load set. As weight changes aren't trivial for the fair class, set_load_weight() calls fair.c::reweight_task() for fair class tasks.

However, set_load_weight() first tests task_has_idle_policy() on entry and skips calling reweight_task() for SCHED_IDLE tasks. This is buggy as SCHED_IDLE tasks are just fair tasks with a very low weight and they would incorrectly skip load, vlag and position updates.

Fix it by updating reweight_task() to take struct load_weight as idle weight can't be expressed with prio and making set_load_weight() call reweight_task() for SCHED_IDLE tasks too when @update_load is set.

Fixes: 9059393e4ec1 ("sched/fair: Use reweight_entity() for set_user_nice()") Suggested-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Tejun Heo tj@kernel.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: stable@vger.kernel.org # v4.15+ Link: http://lkml.kernel.org/r/20240624102331.GI31592@noisy.programming.kicks-ass....

diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 0935f9d4bb7b..747683487be7 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1328,27 +1328,24 @@ int tg_nop(struct task_group *tg, void *data) void set_load_weight(struct task_struct *p, bool update_load) { int prio = p->static_prio - MAX_RT_PRIO; - struct load_weight *load = &p->se.load; + struct load_weight lw;

- /* - * SCHED_IDLE tasks get minimal weight: - */ if (task_has_idle_policy(p)) { - load->weight = scale_load(WEIGHT_IDLEPRIO); - load->inv_weight = WMULT_IDLEPRIO; - return; + lw.weight = scale_load(WEIGHT_IDLEPRIO); + lw.inv_weight = WMULT_IDLEPRIO; + } else { + lw.weight = scale_load(sched_prio_to_weight[prio]); + lw.inv_weight = sched_prio_to_wmult[prio]; }

/* * SCHED_OTHER tasks have to update their load when changing their * weight */ - if (update_load && p->sched_class == &fair_sched_class) { - reweight_task(p, prio); - } else { - load->weight = scale_load(sched_prio_to_weight[prio]); - load->inv_weight = sched_prio_to_wmult[prio]; - } + if (update_load && p->sched_class == &fair_sched_class) + reweight_task(p, &lw); + else + p->se.load = lw; }

#ifdef CONFIG_UCLAMP_TASK diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 41b58387023d..f205e2482690 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -3835,15 +3835,14 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, } }

-void reweight_task(struct task_struct *p, int prio) +void reweight_task(struct task_struct *p, const struct load_weight *lw) { struct sched_entity *se = &p->se; struct cfs_rq *cfs_rq = cfs_rq_of(se); struct load_weight *load = &se->load; - unsigned long weight = scale_load(sched_prio_to_weight[prio]);

- reweight_entity(cfs_rq, se, weight); - load->inv_weight = sched_prio_to_wmult[prio]; + reweight_entity(cfs_rq, se, lw->weight); + load->inv_weight = lw->inv_weight; }

static inline int throttled_hierarchy(struct cfs_rq *cfs_rq); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 62fd8bc6fd08..9ab53435debd 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2509,7 +2509,7 @@ extern void init_sched_dl_class(void); extern void init_sched_rt_class(void); extern void init_sched_fair_class(void);

-extern void reweight_task(struct task_struct *p, int prio); +extern void reweight_task(struct task_struct *p, const struct load_weight *lw);

extern void resched_curr(struct rq *rq); extern void resched_cpu(int cpu);