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authorSebastian Andrzej Siewior <bigeasy@linutronix.de>2022-03-23 00:40:41 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2022-03-23 01:57:02 +0300
commitbe3e67b54b437123e6144da31cf312ddcaa5aef2 (patch)
treead0318c6d1b4da3e2dbe9801f87f46d7b0f64f36 /mm/memcontrol.c
parent2343e88d238f5de973d609d861c505890f94f22e (diff)
downloadlinux-be3e67b54b437123e6144da31cf312ddcaa5aef2.tar.xz
mm/memcg: protect per-CPU counter by disabling preemption on PREEMPT_RT where needed.
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 <bigeasy@linutronix.de> Acked-by: Roman Gushchin <guro@fb.com> Reviewed-by: Shakeel Butt <shakeelb@google.com Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: kernel test robot <oliver.sang@intel.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Michal Hocko <mhocko@suse.com> Cc: Michal Koutný <mkoutny@suse.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vladimir Davydov <vdavydov.dev@gmail.com> Cc: Waiman Long <longman@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memcontrol.c')
-rw-r--r--mm/memcontrol.c56
1 files changed, 55 insertions, 1 deletions
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);