mm/mmap: remove preallocation from do_mas_align_munmap()

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.

Link: https://lkml.kernel.org/r/20230120162650.984577-12-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/mm/mmap.c b/mm/mmap.c
index 17de99f31ff50af324990f4599f4bcc42f528ea2..d46a798c38ab358559a1653c6b3cb4a427a4877f 100644 (file)
--- 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 @@ end_split_failed:
        __mt_destroy(&mt_detach);
 start_split_failed:
 map_count_exceeded:
-       mas_destroy(mas);
        return error;
 }