mm: introduce __vm_flags_mod and use it in untrack_pfn

There are scenarios when vm_flags can be modified without exclusive
mmap_lock, such as:
- after VMA was isolated and mmap_lock was downgraded or dropped
- in exit_mmap when there are no other mm users and locking is unnecessary
Introduce __vm_flags_mod to avoid assertions when the caller takes
responsibility for the required locking.
Pass a hint to untrack_pfn to conditionally use __vm_flags_mod for
flags modification to avoid assertion.

Link: https://lkml.kernel.org/r/20230126193752.297968-7-surenb@google.com
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
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: Davidlohr Bueso <dave@stgolabs.net>
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: Mel Gorman <mgorman@techsingularity.net>
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>

2 files changed, 15 insertions, 4 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ce6d9d765aae..27b34f7730e7 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -657,6 +657,16 @@ static inline void vm_flags_clear(struct vm_area_struct *vma,
 }
 
 /*
+ * Use only if VMA is not part of the VMA tree or has no other users and
+ * therefore needs no locking.
+ */
+static inline void __vm_flags_mod(struct vm_area_struct *vma,
+				  vm_flags_t set, vm_flags_t clear)
+{
+	vm_flags_init(vma, (vma->vm_flags | set) & ~clear);
+}
+
+/*
  * Use only when the order of set/clear operations is unimportant, otherwise
  * use vm_flags_{set|clear} explicitly.
  */
@@ -664,7 +674,7 @@ 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);
+	__vm_flags_mod(vma, set, clear);
 }
 
 static inline void vma_set_anonymous(struct vm_area_struct *vma)
@@ -2085,7 +2095,7 @@ static inline void zap_vma_pages(struct vm_area_struct *vma)
 }
 void unmap_vmas(struct mmu_gather *tlb, struct maple_tree *mt,
 		struct vm_area_struct *start_vma, unsigned long start,
-		unsigned long end);
+		unsigned long end, bool mm_wr_locked);
 
 struct mmu_notifier_range;
 
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 5fd45454c073..c63cd44777ec 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1185,7 +1185,8 @@ static inline int track_pfn_copy(struct vm_area_struct *vma)
  * can be for the entire vma (in which case pfn, size are zero).
  */
 static inline void untrack_pfn(struct vm_area_struct *vma,
-			       unsigned long pfn, unsigned long size)
+			       unsigned long pfn, unsigned long size,
+			       bool mm_wr_locked)
 {
 }
 
@@ -1203,7 +1204,7 @@ extern void track_pfn_insert(struct vm_area_struct *vma, pgprot_t *prot,
 			     pfn_t pfn);
 extern int track_pfn_copy(struct vm_area_struct *vma);
 extern void untrack_pfn(struct vm_area_struct *vma, unsigned long pfn,
-			unsigned long size);
+			unsigned long size, bool mm_wr_locked);
 extern void untrack_pfn_moved(struct vm_area_struct *vma);
 #endif