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X-CSE-ConnectionGUID: e51tmfzQTkiQiF6ocrPJ6A== X-CSE-MsgGUID: FkC2jVFeQ5ue5pTl8Yq+WQ== X-IronPort-AV: E=McAfee;i="6800,10657,11893"; a="106272985" X-IronPort-AV: E=Sophos;i="6.25,256,1779174000"; d="scan'208";a="106272985" Received: from fmviesa010.fm.intel.com ([10.60.135.150]) by fmvoesa102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 01 Sep 2026 17:03:57 -0700 X-CSE-ConnectionGUID: /z/QCYmlRButVJ3u2YlN8A== X-CSE-MsgGUID: W5+9GGHUTz2HpPZKxYFwFw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,256,1779174000"; d="scan'208";a="265531792" Received: from b04f130c83f2.jf.intel.com ([10.165.154.98]) by fmviesa010.fm.intel.com with ESMTP; 01 Sep 2026 17:03:42 -0700 From: Tim Chen To: Peter Zijlstra , Ingo Molnar Cc: Tim Chen , Chen Yu , Hyunwoo Kim , Kees Cook , Christian Brauner , Alexander Viro , Jan Kara , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Shrikanth Hegde , Qais Yousef , Aaron Lu , Srikar Dronamraju , Vineeth Remanan Pillai , linux-kernel@vger.kernel.org, linux-mm@kvack.org, "chen . yu @ linux . dev" Subject: [PATCH 1/2] sched/cache: Decouple sched_cache_group from mm Date: Tue, 1 Sep 2026 17:08:55 -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: rspam07 X-Rspamd-Queue-Id: 4BC33A0009 X-Stat-Signature: 4d4znhetecnm8o4x47ec3y8ipdgk9azo X-HE-Tag: 1788307442-937686 X-HE-Meta: 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 bYnr8god bAdSX4ePeB1JC+YA6E7l7yD6X0AjYNlSiq8HJ0n5ZkQPqEb/yc5TUOHHoX2l0EfdJ0qMLyYIafvb3Oqm3xLMSxqP/y+vsVE2VG+ttBb6vwl7qg9F/UB8AF8rACOrxq62pQwvX0dKK21EFyvjMyU6WtxaZnDPyk4r1DsluxHB8q7L8nQrTF4sHObQihSpzy9NdhGmcGf9SfqwTtzPpOMwTxngvrDF2IOa43ewKtEBJg7IAiJ9fNKoAGR1LjRz540ZeT1Zc62G+J1Em/cTKOlfENte3KA== 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. Access sched_cache_group directly from a task instead of having to go through a task's mm. This allows us to later add a refcount on sched_cache_group when a task links to it, preventing 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 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 8dff37059faf..8587dcbaa1cf 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1489,7 +1489,7 @@ 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 @@ -1534,7 +1534,7 @@ 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))); } @@ -1611,12 +1611,20 @@ 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); @@ -1627,18 +1635,35 @@ 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 */ @@ -1696,7 +1721,7 @@ 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); @@ -1739,11 +1764,15 @@ 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); @@ -1756,11 +1785,11 @@ 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); @@ -1784,19 +1813,19 @@ 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); } } @@ -1808,7 +1837,7 @@ 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); @@ -1880,12 +1909,12 @@ 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; @@ -1893,8 +1922,8 @@ 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; } @@ -1917,8 +1946,10 @@ 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; @@ -1951,7 +1982,7 @@ 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)); @@ -1960,7 +1991,7 @@ 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 @@ -1969,10 +2000,10 @@ 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); } @@ -3776,18 +3807,19 @@ 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 } @@ -10703,18 +10735,18 @@ static enum llc_mig can_migrate_llc_task(int src_cpu, int dst_cpu, int 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