[PATCH] mm/mmap: Preallocate maple nodes for brk vma expansion

[Liam Howlett]

If the brk VMA is the last vma in a maple node and meets the rare
criteria that it can be expanded, then preallocation is necessary to
avoid a potential fs_reclaim circular lock issue on low resources.

At the same time use the actual vma start address (unaligned) when
calling vma_adjust_trans_huge().

Fixes: 2e7ce7d354f2 (mm/mmap: change do_brk_flags() to expand existing VMA and add do_brk_munmap())
Reported-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
---
 mm/mmap.c | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 6e447544f07d..74c0e3784500 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2942,17 +2942,18 @@ static int do_brk_flags(struct ma_state *mas, struct vm_area_struct *vma,
 	if (vma &&
 	    (!vma->anon_vma || list_is_singular(&vma->anon_vma_chain)) &&
 	    ((vma->vm_flags & ~VM_SOFTDIRTY) == flags)) {
-		mas->index = vma->vm_start;
-		mas->last = addr + len - 1;
-		vma_adjust_trans_huge(vma, addr, addr + len, 0);
+		mas_set_range(mas, vma->vm_start, addr + len - 1);
+		if (mas_preallocate(mas, vma, GFP_KERNEL))
+			return -ENOMEM;
+
+		vma_adjust_trans_huge(vma, vma->vm_start, addr + len, 0);
 		if (vma->anon_vma) {
 			anon_vma_lock_write(vma->anon_vma);
 			anon_vma_interval_tree_pre_update_vma(vma);
 		}
 		vma->vm_end = addr + len;
 		vma->vm_flags |= VM_SOFTDIRTY;
-		if (mas_store_gfp(mas, vma, GFP_KERNEL))
-			goto mas_expand_failed;
+		mas_store_prealloc(mas, vma);
 
 		if (vma->anon_vma) {
 			anon_vma_interval_tree_post_update_vma(vma);
@@ -2993,13 +2994,6 @@ static int do_brk_flags(struct ma_state *mas, struct vm_area_struct *vma,
 vma_alloc_fail:
 	vm_unacct_memory(len >> PAGE_SHIFT);
 	return -ENOMEM;
-
-mas_expand_failed:
-	if (vma->anon_vma) {
-		anon_vma_interval_tree_post_update_vma(vma);
-		anon_vma_unlock_write(vma->anon_vma);
-	}
-	return -ENOMEM;
 }
 
 int vm_brk_flags(unsigned long addr, unsigned long request, unsigned long flags)
-- 
2.35.1