mm: introduce vma->vm_flags wrapper functions

vm_flags are among VMA attributes which affect decisions like VMA merging
and splitting.  Therefore all vm_flags modifications are performed after
taking exclusive mmap_lock to prevent vm_flags updates racing with such
operations.  Introduce modifier functions for vm_flags to be used whenever
flags are updated.  This way we can better check and control correct
locking behavior during these updates.

Link: https://lkml.kernel.org/r/20230126193752.297968-3-surenb@google.comSigned-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Davidlohr Bueso <dave@stgolabs.net>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arjun Roy <arjunroy@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: David Howells <dhowells@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Greg Thelen <gthelen@google.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jann Horn <jannh@google.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Laurent Dufour <ldufour@linux.ibm.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Minchan Kim <minchan@google.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Oskolkov <posk@google.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Punit Agrawal <punit.agrawal@bytedance.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Sebastian Reichel <sebastian.reichel@collabora.com>
Cc: Shakeel Butt <shakeelb@google.com>
Cc: Soheil Hassas Yeganeh <soheil@google.com>
Cc: Song Liu <songliubraving@fb.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/mm.h

@@ -627,6 +627,46 @@ static inline void vma_init(struct vm_area_struct *vma, struct mm_struct *mm)
 	INIT_LIST_HEAD(&vma->anon_vma_chain);
 }
 
+/* Use when VMA is not part of the VMA tree and needs no locking */
+static inline void vm_flags_init(struct vm_area_struct *vma,
+				 vm_flags_t flags)
+{
+	ACCESS_PRIVATE(vma, __vm_flags) = flags;
+}
+
+/* Use when VMA is part of the VMA tree and modifications need coordination */
+static inline void vm_flags_reset(struct vm_area_struct *vma,
+				  vm_flags_t flags)
+{
+	mmap_assert_write_locked(vma->vm_mm);
+	vm_flags_init(vma, flags);
+}
+
+static inline void vm_flags_set(struct vm_area_struct *vma,
+				vm_flags_t flags)
+{
+	mmap_assert_write_locked(vma->vm_mm);
+	ACCESS_PRIVATE(vma, __vm_flags) |= flags;
+}
+
+static inline void vm_flags_clear(struct vm_area_struct *vma,
+				  vm_flags_t flags)
+{
+	mmap_assert_write_locked(vma->vm_mm);
+	ACCESS_PRIVATE(vma, __vm_flags) &= ~flags;
+}
+
+/*
+ * Use only when the order of set/clear operations is unimportant, otherwise
+ * use vm_flags_{set|clear} explicitly.
+ */
+static inline void vm_flags_mod(struct vm_area_struct *vma,
+				vm_flags_t set, vm_flags_t clear)
+{
+	mmap_assert_write_locked(vma->vm_mm);
+	vm_flags_init(vma, (vma->vm_flags | set) & ~clear);
+}
+
 static inline void vma_set_anonymous(struct vm_area_struct *vma)
 {
 	vma->vm_ops = NULL;

include/linux/mm_types.h

@@ -491,7 +491,15 @@ struct vm_area_struct {
 	 * See vmf_insert_mixed_prot() for discussion.
 	 */
 	pgprot_t vm_page_prot;
-	unsigned long vm_flags;		/* Flags, see mm.h. */
+
+	/*
+	 * Flags, see mm.h.
+	 * To modify use vm_flags_{init|reset|set|clear|mod} functions.
+	 */
+	union {
+		const vm_flags_t vm_flags;
+		vm_flags_t __private __vm_flags;
+	};
 
 	/*
 	 * For areas with an address space and backing store,