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X-CSE-ConnectionGUID: Inftv7plTd2kUIc0ye0ZDA== X-CSE-MsgGUID: oPetZqblQym6KWTvaZkA8A== X-IronPort-AV: E=McAfee;i="6800,10657,11901"; a="89453828" X-IronPort-AV: E=Sophos;i="6.27,95,1787036400"; d="scan'208";a="89453828" Received: from orviesa003.jf.intel.com ([10.64.159.143]) by orvoesa111.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Sep 2026 10:40:52 -0700 X-CSE-ConnectionGUID: rmltQ60YQxmnoyF6tpw5lA== X-CSE-MsgGUID: Iax3Joh0TFeIm2CtQ2sinQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.27,95,1787036400"; d="scan'208";a="275222021" Received: from b04f130c83f2.jf.intel.com ([10.165.154.98]) by orviesa003.jf.intel.com with ESMTP; 10 Sep 2026 10:40:51 -0700 From: Tim Chen To: Peter Zijlstra , Ingo Molnar Cc: Tim Chen , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Kees Cook , Christian Brauner , Alexander Viro , Jan Kara , Shrikanth Hegde , Qais Yousef , Aaron Lu , Srikar Dronamraju , Vineeth Remanan Pillai , Ricardo Neri-Calderon , Chen Yu , Lu Wang , Hyunwoo Kim , Zhan Xusheng , Zhan Xusheng , Yi Lai , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: [PATCH 3/4] sched/cache: Decouple sched_cache_group from mm Date: Thu, 10 Sep 2026 10:46:11 -0700 Message-Id: X-Mailer: git-send-email 2.32.0 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 467731C000B X-Stat-Signature: ea3ahwwn8fgpj8ab1bu66xz43emckfq5 X-HE-Tag: 1789062053-313367 X-HE-Meta: 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 Yqd+Erl0 Y+fhw0qIcVnBlqpSYvRvpejzy3sRv5xhrF4PT/y1ULzpMk//yogQxaXIBEhR3ALQgo77ag1kmf9DWqM6RKiAJSewgrXVChzPQzaGRh7s4p9UG6Xej6QAdzijrgpYIEkNAGNCW4ko77doqS5oUuqCu/6+Zup69d9/Kdwtw++Uxvk2menrmKl2v+E/3yYYxLlPJQUx9l5CabzQmHdNJfNxws+7JdEdk3LiI73cSaxXW+ygZKzISUiS2EPaVSe9f7+bffb2rVhaLqzOG06nkKQ2VZ4rpWSoQC6AOjInodGPozN2w1WQwJvm40KmFORwhWW5uvxGUPnnp0OWgTyQYpTA8dyZj4Y0Nmr9ILG7w Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Currently the sched cache grouping is by mm and the scheduling statistics sched_cache_stat lives in the mm structure. This ties the life cycle of scheduling stats with mm. In account_mm_sched(), the scheduling stats are accessed by task->mm->sc_stat. However, a task may be switching mm on one CPU when another CPU is running account_mm_sched(), and possibly accessing the old mm that was freed. This problem was found when running tests with KASAN by Hyunwoo. https://lore.kernel.org/lkml/apPb-Dr4nPYuHQOK@v4bel/ Instead of serializing the mm access by introducing extra acquisition of rq lock in the mm free path, extract sched_cache_stat from mm_struct, rename it as sched_cache_group and manage its life cycle apart from mm_struct with its own ref counting. This allows us in the next patch access sched_cache_group directly from task, and add a refcount on sched_cache_group when a task links to it. This prevents the use after free issue when accessing stale and released old mm and its sched cache stat a task switches to a new mm while account_mm_sched() is done elsewhere. The other benefit of this restructure is in the future, the grouping of tasks to a LLC would have the flexibility to be associated with a user defined grouping, or cgroup, cookie group, numa_group or others instead of just with a single mm address space. Rename sched_cache_stat to sched_cache_group and turn it into a refcounted object allocated from mm_struct. The mm_struct now holds a pointer (sched_cache_grp) to this object instead of embedding it. Introduce kernel/sched/cache_sched.c to host the cache aware scheduling helpers and define sched_cache_group_put() there. Meanwhile skip kthreads in account_mm_sched(), consistent with task_tick_cache(). Reported-by: Hyunwoo Kim Closes: https://lore.kernel.org/lkml/apPb-Dr4nPYuHQOK@v4bel/ Tested-by: Hyunwoo Kim Fixes: df0d98475954 ("sched/cache: Introduce infrastructure for cache-aware load balancing") Co-developed-by: Chen Yu Signed-off-by: Chen Yu Signed-off-by: Tim Chen --- include/linux/mm_types.h | 15 ++--- include/linux/sched.h | 8 ++- kernel/exit.c | 6 +- kernel/sched/build_utility.c | 4 ++ kernel/sched/cache_sched.c | 20 ++++++ kernel/sched/fair.c | 118 ++++++++++++++++++++++------------- 6 files changed, 113 insertions(+), 58 deletions(-) create mode 100644 kernel/sched/cache_sched.c diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 6d815f6440c9..f3e5a2fadbe5 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -1226,7 +1226,7 @@ struct mm_struct { struct mm_mm_cid mm_cid; /* sched_cache related statistics */ - struct sched_cache_stat sc_stat; + struct sched_cache_group *sched_cache_grp; #ifdef CONFIG_MMU atomic_long_t pgtables_bytes; /* size of all page tables */ #endif @@ -1624,8 +1624,9 @@ static inline unsigned int mm_cid_size(void) #endif /* CONFIG_SCHED_MM_CID */ #ifdef CONFIG_SCHED_CACHE -void mm_init_sched(struct mm_struct *mm, - struct sched_cache_time __percpu *pcpu_sched); +int mm_init_sched(struct mm_struct *mm, + struct sched_cache_time __percpu *pcpu_sched); +void mm_destroy_sched(struct mm_struct *mm); static inline int mm_alloc_sched_noprof(struct mm_struct *mm) { @@ -1635,17 +1636,11 @@ static inline int mm_alloc_sched_noprof(struct mm_struct *mm) if (!pcpu_sched) return -ENOMEM; - mm_init_sched(mm, pcpu_sched); - return 0; + return mm_init_sched(mm, pcpu_sched); } #define mm_alloc_sched(...) alloc_hooks(mm_alloc_sched_noprof(__VA_ARGS__)) -static inline void mm_destroy_sched(struct mm_struct *mm) -{ - free_percpu(mm->sc_stat.pcpu_sched); - mm->sc_stat.pcpu_sched = NULL; -} #else /* !CONFIG_SCHED_CACHE */ static inline int mm_alloc_sched(struct mm_struct *mm) { return 0; } diff --git a/include/linux/sched.h b/include/linux/sched.h index 8b3d47a325cc..1f254364f216 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2405,7 +2405,7 @@ struct sched_cache_time { unsigned long epoch; }; -struct sched_cache_stat { +struct sched_cache_group { struct sched_cache_time __percpu *pcpu_sched; raw_spinlock_t lock; unsigned long epoch; @@ -2413,11 +2413,15 @@ struct sched_cache_stat { unsigned long next_scan; unsigned long footprint; int cpu; + refcount_t refcnt; + struct rcu_head rcu; } ____cacheline_aligned_in_smp; +void sched_cache_group_put(struct sched_cache_group *grp); + #else -struct sched_cache_stat { }; +struct sched_cache_group { }; #endif diff --git a/kernel/exit.c b/kernel/exit.c index 97686af89501..006edcc0c2c5 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -560,12 +560,12 @@ static void exit_mm_sched_cache(struct mm_struct *mm) return; /* * No lock protection due to performance considerations. - * Make sure mm->sc_stat.footprint does not become + * Make sure the group footprint does not become * negative. */ - fp = READ_ONCE(mm->sc_stat.footprint); + fp = READ_ONCE(mm->sched_cache_grp->footprint); sub = min(fp, current->total_numa_faults); - WRITE_ONCE(mm->sc_stat.footprint, fp - sub); + WRITE_ONCE(mm->sched_cache_grp->footprint, fp - sub); } #else static inline void exit_mm_sched_cache(struct mm_struct *mm) diff --git a/kernel/sched/build_utility.c b/kernel/sched/build_utility.c index e2cf3b08d4e9..24202893b262 100644 --- a/kernel/sched/build_utility.c +++ b/kernel/sched/build_utility.c @@ -89,6 +89,10 @@ # include "core_sched.c" #endif +#ifdef CONFIG_SCHED_CACHE +# include "cache_sched.c" +#endif + #ifdef CONFIG_PSI # include "psi.c" #endif diff --git a/kernel/sched/cache_sched.c b/kernel/sched/cache_sched.c new file mode 100644 index 000000000000..d492df55f9d5 --- /dev/null +++ b/kernel/sched/cache_sched.c @@ -0,0 +1,20 @@ +// SPDX-License-Identifier: GPL-2.0-only +#include "sched.h" + +static void sched_cache_group_free_rcu(struct rcu_head *rcu) +{ + struct sched_cache_group *grp = + container_of(rcu, struct sched_cache_group, rcu); + + /* free_percpu() may be called from atomic context. */ + free_percpu(grp->pcpu_sched); + kfree(grp); +} + +void sched_cache_group_put(struct sched_cache_group *grp) +{ + if (!grp || !refcount_dec_and_test(&grp->refcnt)) + return; + + call_rcu(&grp->rcu, sched_cache_group_free_rcu); +} diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 32213801ea39..b5a823f0a622 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1502,7 +1502,7 @@ static bool exceed_llc_capacity(struct mm_struct *mm, int cpu) * excluded. */ llc = sd->llc_bytes; - footprint = READ_ONCE(mm->sc_stat.footprint); + footprint = READ_ONCE(mm->sched_cache_grp->footprint); /* * Scale the LLC size by 256*llc_aggr_tolerance @@ -1547,7 +1547,7 @@ static bool invalid_llc_nr(struct mm_struct *mm, struct task_struct *p, if (scale == INT_MAX) return false; - return !fits_capacity((mm->sc_stat.nr_running_avg * cpu_smt_num_threads), + return !fits_capacity((mm->sched_cache_grp->nr_running_avg * cpu_smt_num_threads), (scale * per_cpu(sd_llc_size, cpu))); } @@ -1653,12 +1653,20 @@ static void account_llc_dequeue(struct rq *rq, struct task_struct *p) } } -void mm_init_sched(struct mm_struct *mm, - struct sched_cache_time __percpu *_pcpu_sched) +int mm_init_sched(struct mm_struct *mm, + struct sched_cache_time __percpu *_pcpu_sched) { + struct sched_cache_group *grp; unsigned long epoch = 0; int i; + grp = kzalloc_obj(*grp); + if (!grp) { + free_percpu(_pcpu_sched); + mm->sched_cache_grp = NULL; + return -ENOMEM; + } + for_each_possible_cpu(i) { struct sched_cache_time *pcpu_sched = per_cpu_ptr(_pcpu_sched, i); struct rq *rq = cpu_rq(i); @@ -1669,18 +1677,35 @@ void mm_init_sched(struct mm_struct *mm, epoch = rq->cpu_epoch; } - raw_spin_lock_init(&mm->sc_stat.lock); - mm->sc_stat.epoch = epoch; - mm->sc_stat.cpu = -1; - mm->sc_stat.next_scan = jiffies; - mm->sc_stat.nr_running_avg = 0; - mm->sc_stat.footprint = 0; + raw_spin_lock_init(&grp->lock); + grp->epoch = epoch; + grp->cpu = -1; + grp->next_scan = jiffies; + grp->nr_running_avg = 0; + grp->footprint = 0; + refcount_set(&grp->refcnt, 1); /* - * The update to mm->sc_stat should not be reordered - * before initialization to mm's other fields, in case + * The update to grp->pcpu_sched should not be reordered + * before initialization to grp's other fields, in case * the readers may get invalid mm_sched_epoch, etc. */ - smp_store_release(&mm->sc_stat.pcpu_sched, _pcpu_sched); + smp_store_release(&grp->pcpu_sched, _pcpu_sched); + /* + * Publish the group last. Not every reader qualifies it by + * grp->pcpu_sched - can_migrate_llc_task() only checks that the + * pointer is non-NULL before reading grp->footprint and + * grp->nr_running_avg - so a reachable group must already be + * fully initialized. + */ + mm->sched_cache_grp = grp; + return 0; +} + +void mm_destroy_sched(struct mm_struct *mm) +{ + if (mm->sched_cache_grp) + sched_cache_group_put(mm->sched_cache_grp); + mm->sched_cache_grp = NULL; } /* because why would C be fully specified */ @@ -1738,7 +1763,7 @@ static int get_pref_llc(struct task_struct *p, struct mm_struct *mm) if (!mm) return -1; - mm_sched_cpu = READ_ONCE(mm->sc_stat.cpu); + mm_sched_cpu = READ_ONCE(mm->sched_cache_grp->cpu); if (mm_sched_cpu != -1) { mm_sched_llc = llc_id(mm_sched_cpu); @@ -1781,11 +1806,15 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec) /* * init_task, kthreads and user thread created * by user_mode_thread() don't have mm. + * + * A kthread can temporarily adopt an mm via kthread_use_mm(), + * so p->mm alone does not imply a user task. */ - if (!mm || !mm->sc_stat.pcpu_sched) + if (!mm || p->flags & PF_KTHREAD || !mm->sched_cache_grp || + !mm->sched_cache_grp->pcpu_sched) return; - pcpu_sched = per_cpu_ptr(mm->sc_stat.pcpu_sched, cpu_of(rq)); + pcpu_sched = per_cpu_ptr(mm->sched_cache_grp->pcpu_sched, cpu_of(rq)); scoped_guard (raw_spinlock, &rq->cpu_epoch_lock) { __update_mm_sched(rq, pcpu_sched); @@ -1798,11 +1827,11 @@ void account_mm_sched(struct rq *rq, struct task_struct *p, s64 delta_exec) * If this process hasn't hit task_cache_work() for a while invalidate * its preferred state. */ - if ((long)(epoch - READ_ONCE(mm->sc_stat.epoch)) > llc_epoch_affinity_timeout || + if ((long)(epoch - READ_ONCE(mm->sched_cache_grp->epoch)) > llc_epoch_affinity_timeout || invalid_llc_nr(mm, p, cpu_of(rq)) || exceed_llc_capacity(mm, cpu_of(rq))) { - if (READ_ONCE(mm->sc_stat.cpu) != -1) - WRITE_ONCE(mm->sc_stat.cpu, -1); + if (READ_ONCE(mm->sched_cache_grp->cpu) != -1) + WRITE_ONCE(mm->sched_cache_grp->cpu, -1); } mm_sched_llc = get_pref_llc(p, mm); @@ -1826,19 +1855,19 @@ static void task_tick_cache(struct rq *rq, struct task_struct *p) return; if (!mm || p->flags & PF_KTHREAD || - !mm->sc_stat.pcpu_sched) + !mm->sched_cache_grp->pcpu_sched) return; epoch = rq->cpu_epoch; /* avoid moving backwards */ - if (time_after_eq(mm->sc_stat.epoch, epoch)) + if (time_after_eq(mm->sched_cache_grp->epoch, epoch)) return; - guard(raw_spinlock)(&mm->sc_stat.lock); + guard(raw_spinlock)(&mm->sched_cache_grp->lock); if (work->next == work) { task_work_add(p, work, TWA_RESUME); - WRITE_ONCE(mm->sc_stat.epoch, epoch); + WRITE_ONCE(mm->sched_cache_grp->epoch, epoch); } } @@ -1850,7 +1879,7 @@ static void get_scan_cpumasks(cpumask_var_t cpus, struct task_struct *p) if (!static_branch_likely(&sched_numa_balancing)) goto out; - cpu = READ_ONCE(p->mm->sc_stat.cpu); + cpu = READ_ONCE(p->mm->sched_cache_grp->cpu); if (cpu != -1) nid = cpu_to_node(cpu); curr_cpu = task_cpu(p); @@ -1922,12 +1951,12 @@ static void task_cache_work(struct callback_head *work) if (p->flags & PF_EXITING) return; - next_scan = READ_ONCE(mm->sc_stat.next_scan); + next_scan = READ_ONCE(mm->sched_cache_grp->next_scan); if (time_before(now, next_scan)) return; /* only 1 thread is allowed to scan */ - if (!try_cmpxchg(&mm->sc_stat.next_scan, &next_scan, + if (!try_cmpxchg(&mm->sched_cache_grp->next_scan, &next_scan, now + max_t(unsigned long, READ_ONCE(llc_epoch_period), 1))) return; @@ -1935,8 +1964,8 @@ static void task_cache_work(struct callback_head *work) curr_cpu = task_cpu(p); if (invalid_llc_nr(mm, p, curr_cpu) || exceed_llc_capacity(mm, curr_cpu)) { - if (READ_ONCE(mm->sc_stat.cpu) != -1) - WRITE_ONCE(mm->sc_stat.cpu, -1); + if (READ_ONCE(mm->sched_cache_grp->cpu) != -1) + WRITE_ONCE(mm->sched_cache_grp->cpu, -1); return; } @@ -1959,8 +1988,10 @@ static void task_cache_work(struct callback_head *work) continue; for_each_cpu(i, sched_domain_span(sd)) { + struct sched_cache_group *grp = mm->sched_cache_grp; + occ = fraction_mm_sched(cpu_rq(i), - per_cpu_ptr(mm->sc_stat.pcpu_sched, i)); + per_cpu_ptr(grp->pcpu_sched, i)); a_occ += occ; if (occ > m_occ) { m_occ = occ; @@ -1993,7 +2024,7 @@ static void task_cache_work(struct callback_head *work) m_a_cpu = m_cpu; } - if (llc_id(cpu) == llc_id(READ_ONCE(mm->sc_stat.cpu))) + if (llc_id(cpu) == llc_id(READ_ONCE(mm->sched_cache_grp->cpu))) curr_m_a_occ = a_occ; cpumask_andnot(cpus, cpus, sched_domain_span(sd)); @@ -2002,7 +2033,7 @@ static void task_cache_work(struct callback_head *work) if (m_a_occ > (2 * curr_m_a_occ)) { /* - * Avoid switching sc_stat.cpu too fast. + * Avoid switching sched_cache_grp->cpu too fast. * The reason to choose 2X is because: * 1. It is better to keep the preferred LLC stable, * rather than changing it frequently and cause migrations @@ -2011,10 +2042,10 @@ static void task_cache_work(struct callback_head *work) * 3. 2X is chosen based on test results, as it delivers * the optimal performance gain so far. */ - WRITE_ONCE(mm->sc_stat.cpu, m_a_cpu); + WRITE_ONCE(mm->sched_cache_grp->cpu, m_a_cpu); } - update_avg_scale(&mm->sc_stat.nr_running_avg, nr_running); + update_avg_scale(&mm->sched_cache_grp->nr_running_avg, nr_running); free_cpumask_var(cpus); } @@ -3822,18 +3853,19 @@ static void task_numa_placement(struct task_struct *p) * heuristic and occasional lost updates are tolerable. * * If a task exits, its corresponding footprint must - * be subtracted from the mm->sc_stat.footprint, otherwise - * the mm->sc_stat.footprint will not converge: - * the exiting thread's footprint remains unchanged/undecayed - * in mm->sc_stat.footprint. See exit_mm(). + * be subtracted from the mm->sched_cache_grp->footprint, + * otherwise the mm->sched_cache_grp->footprint will not + * converge: the exiting thread's footprint remains + * unchanged/undecayed in mm->sched_cache_grp->footprint. + * See exit_mm(). * * Lost updates and unsynchronized subtraction * in exit_mm() can cause footprint + diff to * go negative. Clamp to zero to prevent the * unsigned footprint from wrapping. */ - new_fp = (long)READ_ONCE(p->mm->sc_stat.footprint) + diff; - WRITE_ONCE(p->mm->sc_stat.footprint, + new_fp = (long)READ_ONCE(p->mm->sched_cache_grp->footprint) + diff; + WRITE_ONCE(p->mm->sched_cache_grp->footprint, max(new_fp, 0L)); #endif } @@ -10788,18 +10820,18 @@ static enum llc_mig can_migrate_llc_task(struct lb_env *env, src_cpu = env->src_cpu; dst_cpu = env->dst_cpu; mm = p->mm; - if (!mm) + if (!mm || !mm->sched_cache_grp) return mig_unrestricted; - cpu = READ_ONCE(mm->sc_stat.cpu); + cpu = READ_ONCE(mm->sched_cache_grp->cpu); if (cpu < 0 || cpus_share_cache(src_cpu, dst_cpu)) return mig_unrestricted; /* skip cache aware load balance for too many threads */ if (invalid_llc_nr(mm, p, dst_cpu) || exceed_llc_capacity(mm, dst_cpu)) { - if (READ_ONCE(mm->sc_stat.cpu) != -1) - WRITE_ONCE(mm->sc_stat.cpu, -1); + if (READ_ONCE(mm->sched_cache_grp->cpu) != -1) + WRITE_ONCE(mm->sched_cache_grp->cpu, -1); return mig_unrestricted; } -- 2.32.0