+ mm-mmap-change-detached-vma-locking-scheme.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/mmap: change detached vma locking scheme
has been added to the -mm mm-unstable branch.  Its filename is
     mm-mmap-change-detached-vma-locking-scheme.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mmap-change-detached-vma-locking-scheme.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Liam R. Howlett" <Liam.Howlett@oracle.com>
Subject: mm/mmap: change detached vma locking scheme
Date: Wed, 5 Jul 2023 14:47:49 -0400

Don't set the lock to the mm lock so that the detached VMA tree does not
complain about being unlocked when the mmap_lock is dropped prior to
freeing the tree.

Introduce mt_on_stack() for setting the external lock to NULL only when
LOCKDEP is used.

Move the destroying of the detached tree outside the mmap lock all
together.

Link: https://lkml.kernel.org/r/20230719183142.ktgcmuj2pnlr3h3s@revolver
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oliver Sang <oliver.sang@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/maple_tree.h |    3 +++
 mm/mmap.c                  |    4 ++--
 2 files changed, 5 insertions(+), 2 deletions(-)

--- a/include/linux/maple_tree.h~mm-mmap-change-detached-vma-locking-scheme
+++ a/include/linux/maple_tree.h
@@ -187,10 +187,13 @@ typedef struct lockdep_map *lockdep_map_
 
 #define mt_set_external_lock(mt, lock)					\
 	(mt)->ma_external_lock = &(lock)->dep_map
+
+#define mt_on_stack(mt)			(mt).ma_external_lock = NULL
 #else
 typedef struct { /* nothing */ } lockdep_map_p;
 #define mt_lock_is_held(mt)	1
 #define mt_set_external_lock(mt, lock)	do { } while (0)
+#define mt_on_stack(mt)			do { } while (0)
 #endif
 
 /*
--- a/mm/mmap.c~mm-mmap-change-detached-vma-locking-scheme
+++ a/mm/mmap.c
@@ -2427,7 +2427,7 @@ do_vmi_align_munmap(struct vma_iterator
 	unsigned long locked_vm = 0;
 	MA_STATE(mas_detach, &mt_detach, 0, 0);
 	mt_init_flags(&mt_detach, vmi->mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
-	mt_set_external_lock(&mt_detach, &mm->mmap_lock);
+	mt_on_stack(mt_detach);
 
 	/*
 	 * If we need to split any vma, do it now to save pain later.
@@ -2545,11 +2545,11 @@ do_vmi_align_munmap(struct vma_iterator
 	/* Statistics and freeing VMAs */
 	mas_set(&mas_detach, start);
 	remove_mt(mm, &mas_detach);
-	__mt_destroy(&mt_detach);
 	validate_mm(mm);
 	if (unlock)
 		mmap_read_unlock(mm);
 
+	__mt_destroy(&mt_detach);
 	return 0;
 
 clear_tree_failed:
_

Patches currently in -mm which might be from Liam.Howlett@oracle.com are

mm-mmap-clean-up-validate_mm-calls.patch
maple_tree-relax-lockdep-checks-for-on-stack-trees.patch
mm-mmap-change-detached-vma-locking-scheme.patch
maple_tree-be-more-strict-about-locking.patch