linux-kernel - [PATCH 25/41] mm/mmap: write-lock adjacent VMAs if they can grow into unmapped area

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Date:   Mon,  9 Jan 2023 12:53:20 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     akpm@...ux-foundation.org
Cc:     michel@...pinasse.org, jglisse@...gle.com, mhocko@...e.com,
        vbabka@...e.cz, hannes@...xchg.org, mgorman@...hsingularity.net,
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        peterz@...radead.org, ldufour@...ux.ibm.com,
        laurent.dufour@...ibm.com, paulmck@...nel.org, luto@...nel.org,
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        leewalsh@...gle.com, posk@...gle.com, linux-mm@...ck.org,
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        surenb@...gle.com
Subject: [PATCH 25/41] mm/mmap: write-lock adjacent VMAs if they can grow into
 unmapped area

While unmapping VMAs, adjacent VMAs might be able to grow into the area
being unmapped. In such cases write-lock adjacent VMAs to prevent this
growth.

Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
---
 mm/mmap.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 0d767ce043af..30c7d1c5206e 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2461,11 +2461,13 @@ do_mas_align_munmap(struct ma_state *mas, struct vm_area_struct *vma,
 	 * down_read(mmap_lock) and collide with the VMA we are about to unmap.
 	 */
 	if (downgrade) {
-		if (next && (next->vm_flags & VM_GROWSDOWN))
+		if (next && (next->vm_flags & VM_GROWSDOWN)) {
+			vma_write_lock(next);
 			downgrade = false;
-		else if (prev && (prev->vm_flags & VM_GROWSUP))
+		} else if (prev && (prev->vm_flags & VM_GROWSUP)) {
+			vma_write_lock(prev);
 			downgrade = false;
-		else
+		} else
 			mmap_write_downgrade(mm);
 	}
 
-- 
2.39.0