From be3e67b54b437123e6144da31cf312ddcaa5aef2 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Tue, 22 Mar 2022 14:40:41 -0700 Subject: [PATCH] mm/memcg: protect per-CPU counter by disabling preemption on PREEMPT_RT where needed. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The per-CPU counter are modified with the non-atomic modifier. The consistency is ensured by disabling interrupts for the update. On non PREEMPT_RT configuration this works because acquiring a spinlock_t typed lock with the _irq() suffix disables interrupts. On PREEMPT_RT configurations the RMW operation can be interrupted. Another problem is that mem_cgroup_swapout() expects to be invoked with disabled interrupts because the caller has to acquire a spinlock_t which is acquired with disabled interrupts. Since spinlock_t never disables interrupts on PREEMPT_RT the interrupts are never disabled at this point. The code is never called from in_irq() context on PREEMPT_RT therefore disabling preemption during the update is sufficient on PREEMPT_RT. The sections which explicitly disable interrupts can remain on PREEMPT_RT because the sections remain short and they don't involve sleeping locks (memcg_check_events() is doing nothing on PREEMPT_RT). Disable preemption during update of the per-CPU variables which do not explicitly disable interrupts. Link: https://lkml.kernel.org/r/20220226204144.1008339-4-bigeasy@linutronix.de Signed-off-by: Sebastian Andrzej Siewior Acked-by: Roman Gushchin Reviewed-by: Shakeel Butt Cc: kernel test robot Cc: Michal Hocko Cc: Michal Hocko Cc: Michal Koutný Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Vladimir Davydov Cc: Waiman Long Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/memcontrol.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 55 insertions(+), 1 deletion(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 6c61b4ec041e..bc60694b4e45 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -629,6 +629,35 @@ static DEFINE_SPINLOCK(stats_flush_lock); static DEFINE_PER_CPU(unsigned int, stats_updates); static atomic_t stats_flush_threshold = ATOMIC_INIT(0); +/* + * Accessors to ensure that preemption is disabled on PREEMPT_RT because it can + * not rely on this as part of an acquired spinlock_t lock. These functions are + * never used in hardirq context on PREEMPT_RT and therefore disabling preemtion + * is sufficient. + */ +static void memcg_stats_lock(void) +{ +#ifdef CONFIG_PREEMPT_RT + preempt_disable(); +#else + VM_BUG_ON(!irqs_disabled()); +#endif +} + +static void __memcg_stats_lock(void) +{ +#ifdef CONFIG_PREEMPT_RT + preempt_disable(); +#endif +} + +static void memcg_stats_unlock(void) +{ +#ifdef CONFIG_PREEMPT_RT + preempt_enable(); +#endif +} + static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val) { unsigned int x; @@ -705,6 +734,27 @@ void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec); memcg = pn->memcg; + /* + * The caller from rmap relay on disabled preemption becase they never + * update their counter from in-interrupt context. For these two + * counters we check that the update is never performed from an + * interrupt context while other caller need to have disabled interrupt. + */ + __memcg_stats_lock(); + if (IS_ENABLED(CONFIG_DEBUG_VM) && !IS_ENABLED(CONFIG_PREEMPT_RT)) { + switch (idx) { + case NR_ANON_MAPPED: + case NR_FILE_MAPPED: + case NR_ANON_THPS: + case NR_SHMEM_PMDMAPPED: + case NR_FILE_PMDMAPPED: + WARN_ON_ONCE(!in_task()); + break; + default: + WARN_ON_ONCE(!irqs_disabled()); + } + } + /* Update memcg */ __this_cpu_add(memcg->vmstats_percpu->state[idx], val); @@ -712,6 +762,7 @@ void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, __this_cpu_add(pn->lruvec_stats_percpu->state[idx], val); memcg_rstat_updated(memcg, val); + memcg_stats_unlock(); } /** @@ -794,8 +845,10 @@ void __count_memcg_events(struct mem_cgroup *memcg, enum vm_event_item idx, if (mem_cgroup_disabled()) return; + memcg_stats_lock(); __this_cpu_add(memcg->vmstats_percpu->events[idx], count); memcg_rstat_updated(memcg, count); + memcg_stats_unlock(); } static unsigned long memcg_events(struct mem_cgroup *memcg, int event) @@ -7154,8 +7207,9 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry) * important here to have the interrupts disabled because it is the * only synchronisation we have for updating the per-CPU variables. */ - VM_BUG_ON(!irqs_disabled()); + memcg_stats_lock(); mem_cgroup_charge_statistics(memcg, -nr_entries); + memcg_stats_unlock(); memcg_check_events(memcg, page_to_nid(page)); css_put(&memcg->css);