linux-kernel - [PATCH] mm/mmap: Fix locking issues in vma

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Date:   Tue, 12 Jul 2022 14:49:43 +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>
Subject: [PATCH] mm/mmap: Fix locking issues in vma_expand()

Hugh noted that the locking was mixed up in vma_expand(), revert to the
correct order.

Fixes: b2c87578e0ea (mm/mmap: use advanced maple tree API for mmap_region())
Suggested-by: Hugh Dickins <hughd@...gle.com>
Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
 mm/mmap.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 9eb663cde5c7..9a07bc18e6aa 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -574,7 +574,8 @@ inline int vma_expand(struct ma_state *mas, struct vm_area_struct *vma,
 		if (next->anon_vma && !vma->anon_vma) {
 			int error;
 
-			vma->anon_vma = next->anon_vma;
+			anon_vma = next->anon_vma;
+			vma->anon_vma = anon_vma;
 			error = anon_vma_clone(vma, next);
 			if (error)
 				return error;
@@ -592,16 +593,19 @@ inline int vma_expand(struct ma_state *mas, struct vm_area_struct *vma,
 
 	vma_adjust_trans_huge(vma, start, end, 0);
 
+	if (file) {
+		mapping = file->f_mapping;
+		root = &mapping->i_mmap;
+		uprobe_munmap(vma, vma->vm_start, vma->vm_end);
+		i_mmap_lock_write(mapping);
+	}
+
 	if (anon_vma) {
 		anon_vma_lock_write(anon_vma);
 		anon_vma_interval_tree_pre_update_vma(vma);
 	}
 
 	if (file) {
-		mapping = file->f_mapping;
-		root = &mapping->i_mmap;
-		uprobe_munmap(vma, vma->vm_start, vma->vm_end);
-		i_mmap_lock_write(mapping);
 		flush_dcache_mmap_lock(mapping);
 		vma_interval_tree_remove(vma, root);
 	}
@@ -622,16 +626,15 @@ inline int vma_expand(struct ma_state *mas, struct vm_area_struct *vma,
 		__remove_shared_vm_struct(next, file, mapping);
 	}
 
-	if (file) {
-		i_mmap_unlock_write(mapping);
-		uprobe_mmap(vma);
-	}
-
 	if (anon_vma) {
 		anon_vma_interval_tree_post_update_vma(vma);
 		anon_vma_unlock_write(anon_vma);
 	}
 
+	if (file) {
+		i_mmap_unlock_write(mapping);
+		uprobe_mmap(vma);
+	}
 
 	if (remove_next) {
 		if (file) {
-- 
2.35.1