linux-kernel - [PATCH 1/3] mmap: Remove do_brk

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Date:   Tue, 19 Jul 2022 19:14:01 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>
CC:     Yu Zhao <yuzhao@...gle.com>
Subject: [PATCH 1/3] mmap: Remove do_brk_munmap() optimization

This optimization does not work with the locking.

Fixes: f12fee814843 (mm/mmap: change do_brk_flags() to expand existing VMA and add do_brk_munmap())
Suggested-by: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
 mm/mmap.c | 61 ++-----------------------------------------------------
 1 file changed, 2 insertions(+), 59 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 2f19976ea817..4fc1b3098c91 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2861,67 +2861,10 @@ static int do_brk_munmap(struct ma_state *mas, struct vm_area_struct *vma,
 			 struct list_head *uf)
 {
 	struct mm_struct *mm = vma->vm_mm;
-	struct vm_area_struct unmap;
-	unsigned long unmap_pages;
-	int ret = 1;
+	int ret;
 
 	arch_unmap(mm, newbrk, oldbrk);
-
-	if (likely((vma->vm_end < oldbrk) ||
-		   ((vma->vm_start == newbrk) && (vma->vm_end == oldbrk)))) {
-		/* remove entire mapping(s) */
-		mas_set(mas, newbrk);
-		if (vma->vm_start != newbrk)
-			mas_reset(mas); /* cause a re-walk for the first overlap. */
-		ret = __do_munmap(mm, newbrk, oldbrk - newbrk, uf, true);
-		goto munmap_full_vma;
-	}
-
-	vma_init(&unmap, mm);
-	unmap.vm_start = newbrk;
-	unmap.vm_end = oldbrk;
-	ret = userfaultfd_unmap_prep(&unmap, newbrk, oldbrk, uf);
-	if (ret)
-		return ret;
-	ret = 1;
-
-	/* Change the oldbrk of vma to the newbrk of the munmap area */
-	vma_adjust_trans_huge(vma, vma->vm_start, newbrk, 0);
-	if (mas_preallocate(mas, vma, GFP_KERNEL))
-		return -ENOMEM;
-
-	if (vma->anon_vma) {
-		anon_vma_lock_write(vma->anon_vma);
-		anon_vma_interval_tree_pre_update_vma(vma);
-	}
-
-	vma->vm_end = newbrk;
-	vma_init(&unmap, mm);
-	unmap.vm_start = newbrk;
-	unmap.vm_end = oldbrk;
-	if (vma->anon_vma)
-		vma_set_anonymous(&unmap);
-
-	vma_mas_remove(&unmap, mas);
-
-	vmacache_invalidate(vma->vm_mm);
-	if (vma->anon_vma) {
-		anon_vma_interval_tree_post_update_vma(vma);
-		anon_vma_unlock_write(vma->anon_vma);
-	}
-
-	unmap_pages = vma_pages(&unmap);
-	if (vma->vm_flags & VM_LOCKED)
-		mm->locked_vm -= unmap_pages;
-
-	mmap_write_downgrade(mm);
-	unmap_region(mm, &unmap, vma, newbrk, oldbrk);
-	/* Statistics */
-	vm_stat_account(mm, vma->vm_flags, -unmap_pages);
-	if (vma->vm_flags & VM_ACCOUNT)
-		vm_unacct_memory(unmap_pages);
-
-munmap_full_vma:
+	ret = __do_munmap(mm, newbrk, oldbrk - newbrk, uf, true);
 	validate_mm_mt(mm);
 	return ret;
 }
-- 
2.35.1