[PATCH] mm/munlock: Protect the per-CPU pagevec by a local_lock_t.

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

The access to mlock_pvec is protected by disabling preemption via
get_cpu_var() or implicit by having preemption disabled by the caller
(in mlock_page_drain() case).
This breaks on PREEMPT_RT since folio_lruvec_lock_irq() acquires a
sleeping lock in this section.

Create struct mlock_pvec which consits of the local_lock_t and the
pagevec. Acquire the local_lock() before accessing the per-CPU pagevec.
Replace mlock_page_drain() with a _local() version which is invoked on
the local CPU and acquires the local_lock_t and a _remote() version
which uses the pagevec from a remote CPU which offline.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 mm/internal.h   |  6 ++++--
 mm/migrate.c    |  2 +-
 mm/mlock.c      | 46 ++++++++++++++++++++++++++++++++++++----------
 mm/page_alloc.c |  1 +
 mm/rmap.c       |  4 ++--
 mm/swap.c       |  4 +++-
 6 files changed, 47 insertions(+), 16 deletions(-)

diff --git a/mm/internal.h b/mm/internal.h
index 9be0227ccc942..50c3fd71d7ddd 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -456,7 +456,8 @@ static inline void munlock_vma_page(struct page *page,
 }
 void mlock_new_page(struct page *page);
 bool need_mlock_page_drain(int cpu);
-void mlock_page_drain(int cpu);
+void mlock_page_drain_local(void);
+void mlock_page_drain_remote(int cpu);
 
 extern pmd_t maybe_pmd_mkwrite(pmd_t pmd, struct vm_area_struct *vma);
 
@@ -547,7 +548,8 @@ static inline void munlock_vma_page(struct page *page,
 			struct vm_area_struct *vma, bool compound) { }
 static inline void mlock_new_page(struct page *page) { }
 static inline bool need_mlock_page_drain(int cpu) { return false; }
-static inline void mlock_page_drain(int cpu) { }
+static inline void mlock_page_drain_local(void) { }
+static inline void mlock_page_drain_remote(int cpu) { }
 static inline void vunmap_range_noflush(unsigned long start, unsigned long end)
 {
 }
diff --git a/mm/migrate.c b/mm/migrate.c
index 3d60823afd2d3..de175e2fdba5d 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -246,7 +246,7 @@ static bool remove_migration_pte(struct folio *folio,
 			set_pte_at(vma->vm_mm, pvmw.address, pvmw.pte, pte);
 		}
 		if (vma->vm_flags & VM_LOCKED)
-			mlock_page_drain(smp_processor_id());
+			mlock_page_drain_local();
 
 		trace_remove_migration_pte(pvmw.address, pte_val(pte),
 					   compound_order(new));
diff --git a/mm/mlock.c b/mm/mlock.c
index efd2dd2943dec..6e503b8690f52 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -28,7 +28,14 @@
 
 #include "internal.h"
 
-static DEFINE_PER_CPU(struct pagevec, mlock_pvec);
+struct mlock_pvec {
+	local_lock_t lock;
+	struct pagevec vec;
+};
+
+static DEFINE_PER_CPU(struct mlock_pvec, mlock_pvec) = {
+	.lock = INIT_LOCAL_LOCK(lock),
+};
 
 bool can_do_mlock(void)
 {
@@ -203,18 +210,30 @@ static void mlock_pagevec(struct pagevec *pvec)
 	pagevec_reinit(pvec);
 }
 
-void mlock_page_drain(int cpu)
+void mlock_page_drain_local(void)
 {
 	struct pagevec *pvec;
 
-	pvec = &per_cpu(mlock_pvec, cpu);
+	local_lock(&mlock_pvec.lock);
+	pvec = this_cpu_ptr(&mlock_pvec.vec);
+	if (pagevec_count(pvec))
+		mlock_pagevec(pvec);
+	local_unlock(&mlock_pvec.lock);
+}
+
+void mlock_page_drain_remote(int cpu)
+{
+	struct pagevec *pvec;
+
+	WARN_ON_ONCE(cpu_online(cpu));
+	pvec = &per_cpu(mlock_pvec.vec, cpu);
 	if (pagevec_count(pvec))
 		mlock_pagevec(pvec);
 }
 
 bool need_mlock_page_drain(int cpu)
 {
-	return pagevec_count(&per_cpu(mlock_pvec, cpu));
+	return pagevec_count(&per_cpu(mlock_pvec.vec, cpu));
 }
 
 /**
@@ -223,7 +242,10 @@ bool need_mlock_page_drain(int cpu)
  */
 void mlock_folio(struct folio *folio)
 {
-	struct pagevec *pvec = &get_cpu_var(mlock_pvec);
+	struct pagevec *pvec;
+
+	local_lock(&mlock_pvec.lock);
+	pvec = this_cpu_ptr(&mlock_pvec.vec);
 
 	if (!folio_test_set_mlocked(folio)) {
 		int nr_pages = folio_nr_pages(folio);
@@ -236,7 +258,7 @@ void mlock_folio(struct folio *folio)
 	if (!pagevec_add(pvec, mlock_lru(&folio->page)) ||
 	    folio_test_large(folio) || lru_cache_disabled())
 		mlock_pagevec(pvec);
-	put_cpu_var(mlock_pvec);
+	local_unlock(&mlock_pvec.lock);
 }
 
 /**
@@ -245,9 +267,11 @@ void mlock_folio(struct folio *folio)
  */
 void mlock_new_page(struct page *page)
 {
-	struct pagevec *pvec = &get_cpu_var(mlock_pvec);
+	struct pagevec *pvec;
 	int nr_pages = thp_nr_pages(page);
 
+	local_lock(&mlock_pvec.lock);
+	pvec = this_cpu_ptr(&mlock_pvec.vec);
 	SetPageMlocked(page);
 	mod_zone_page_state(page_zone(page), NR_MLOCK, nr_pages);
 	__count_vm_events(UNEVICTABLE_PGMLOCKED, nr_pages);
@@ -256,7 +280,7 @@ void mlock_new_page(struct page *page)
 	if (!pagevec_add(pvec, mlock_new(page)) ||
 	    PageHead(page) || lru_cache_disabled())
 		mlock_pagevec(pvec);
-	put_cpu_var(mlock_pvec);
+	local_unlock(&mlock_pvec.lock);
 }
 
 /**
@@ -265,8 +289,10 @@ void mlock_new_page(struct page *page)
  */
 void munlock_page(struct page *page)
 {
-	struct pagevec *pvec = &get_cpu_var(mlock_pvec);
+	struct pagevec *pvec;
 
+	local_lock(&mlock_pvec.lock);
+	pvec = this_cpu_ptr(&mlock_pvec.vec);
 	/*
 	 * TestClearPageMlocked(page) must be left to __munlock_page(),
 	 * which will check whether the page is multiply mlocked.
@@ -276,7 +302,7 @@ void munlock_page(struct page *page)
 	if (!pagevec_add(pvec, page) ||
 	    PageHead(page) || lru_cache_disabled())
 		mlock_pagevec(pvec);
-	put_cpu_var(mlock_pvec);
+	local_unlock(&mlock_pvec.lock);
 }
 
 static int mlock_pte_range(pmd_t *pmd, unsigned long addr,
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f648decfe39d1..94f515845d53a 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8355,6 +8355,7 @@ static int page_alloc_cpu_dead(unsigned int cpu)
 	struct zone *zone;
 
 	lru_add_drain_cpu(cpu);
+	mlock_page_drain_remote(cpu);
 	drain_pages(cpu);
 
 	/*
diff --git a/mm/rmap.c b/mm/rmap.c
index 3eb95fcde7000..90b4956096ef3 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1727,7 +1727,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 		 */
 		page_remove_rmap(subpage, vma, folio_test_hugetlb(folio));
 		if (vma->vm_flags & VM_LOCKED)
-			mlock_page_drain(smp_processor_id());
+			mlock_page_drain_local();
 		folio_put(folio);
 	}
 
@@ -2005,7 +2005,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
 		 */
 		page_remove_rmap(subpage, vma, folio_test_hugetlb(folio));
 		if (vma->vm_flags & VM_LOCKED)
-			mlock_page_drain(smp_processor_id());
+			mlock_page_drain_local();
 		folio_put(folio);
 	}
 
diff --git a/mm/swap.c b/mm/swap.c
index bceff0cb559c9..7e320ec08c6ae 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -624,7 +624,6 @@ void lru_add_drain_cpu(int cpu)
 		pagevec_lru_move_fn(pvec, lru_lazyfree_fn);
 
 	activate_page_drain(cpu);
-	mlock_page_drain(cpu);
 }
 
 /**
@@ -706,6 +705,7 @@ void lru_add_drain(void)
 	local_lock(&lru_pvecs.lock);
 	lru_add_drain_cpu(smp_processor_id());
 	local_unlock(&lru_pvecs.lock);
+	mlock_page_drain_local();
 }
 
 /*
@@ -720,6 +720,7 @@ static void lru_add_and_bh_lrus_drain(void)
 	lru_add_drain_cpu(smp_processor_id());
 	local_unlock(&lru_pvecs.lock);
 	invalidate_bh_lrus_cpu();
+	mlock_page_drain_local();
 }
 
 void lru_add_drain_cpu_zone(struct zone *zone)
@@ -728,6 +729,7 @@ void lru_add_drain_cpu_zone(struct zone *zone)
 	lru_add_drain_cpu(smp_processor_id());
 	drain_local_pages(zone);
 	local_unlock(&lru_pvecs.lock);
+	mlock_page_drain_local();
 }
 
 #ifdef CONFIG_SMP
-- 
2.35.1