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From:   "Liam R. Howlett" <Liam.Howlett@oracle.com>
To:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Andrew Morton <akpm@linux-foundation.org>,
        maple-tree@lists.infradead.org
Cc:     "Liam R. Howlett" <Liam.Howlett@Oracle.com>,
        "Liam R . Howlett" <Liam.Howlett@oracle.com>
Subject: [PATCH v4 11/49] mm/mmap: Remove preallocation from do_mas_align_munmap()
Date:   Fri, 20 Jan 2023 11:26:12 -0500
Message-Id: <20230120162650.984577-12-Liam.Howlett@oracle.com>
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From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>

In preparation of passing the vma state through split, the
pre-allocation that occurs before the split has to be moved to after.
Since the preallocation would then live right next to the store, just
call store instead of preallocating.  This effectively restores the
potential error path of splitting and not munmap'ing which pre-dates the
maple tree.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
---
 mm/mmap.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 09a5b6e00374..83d25fcc2f6d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2329,9 +2329,6 @@ do_mas_align_munmap(struct ma_state *mas, struct vm_area_struct *vma,
 	mt_init_flags(&mt_detach, MT_FLAGS_LOCK_EXTERN);
 	mt_set_external_lock(&mt_detach, &mm->mmap_lock);
 
-	if (mas_preallocate(mas, GFP_KERNEL))
-		return -ENOMEM;
-
 	mas->last = end - 1;
 	/*
 	 * If we need to split any vma, do it now to save pain later.
@@ -2422,8 +2419,6 @@ do_mas_align_munmap(struct ma_state *mas, struct vm_area_struct *vma,
 			goto userfaultfd_error;
 	}
 
-	/* Point of no return */
-	mas_set_range(mas, start, end - 1);
 #if defined(CONFIG_DEBUG_VM_MAPLE_TREE)
 	/* Make sure no VMAs are about to be lost. */
 	{
@@ -2431,6 +2426,7 @@ do_mas_align_munmap(struct ma_state *mas, struct vm_area_struct *vma,
 		struct vm_area_struct *vma_mas, *vma_test;
 		int test_count = 0;
 
+		mas_set_range(mas, start, end - 1);
 		rcu_read_lock();
 		vma_test = mas_find(&test, end - 1);
 		mas_for_each(mas, vma_mas, end - 1) {
@@ -2440,10 +2436,13 @@ do_mas_align_munmap(struct ma_state *mas, struct vm_area_struct *vma,
 		}
 		rcu_read_unlock();
 		BUG_ON(count != test_count);
-		mas_set_range(mas, start, end - 1);
 	}
 #endif
-	mas_store_prealloc(mas, NULL);
+	/* Point of no return */
+	mas_set_range(mas, start, end - 1);
+	if (mas_store_gfp(mas, NULL, GFP_KERNEL))
+		return -ENOMEM;
+
 	mm->map_count -= count;
 	/*
 	 * Do not downgrade mmap_lock if we are next to VM_GROWSDOWN or
@@ -2475,7 +2474,6 @@ do_mas_align_munmap(struct ma_state *mas, struct vm_area_struct *vma,
 	__mt_destroy(&mt_detach);
 start_split_failed:
 map_count_exceeded:
-	mas_destroy(mas);
 	return error;
 }
 
-- 
2.35.1