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Date:   Sat, 8 Jul 2023 16:04:00 -0700 (PDT)
From:   Hugh Dickins <hughd@google.com>
To:     Linus Torvalds <torvalds@linux-foundation.org>
cc:     Suren Baghdasaryan <surenb@google.com>, akpm@linux-foundation.org,
        regressions@leemhuis.info, bagasdotme@gmail.com,
        jacobly.alt@gmail.com, willy@infradead.org,
        liam.howlett@oracle.com, david@redhat.com, peterx@redhat.com,
        ldufour@linux.ibm.com, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org,
        linux-arm-kernel@lists.infradead.org, gregkh@linuxfoundation.org,
        regressions@lists.linux.dev, stable@vger.kernel.org
Subject: [PATCH] mm: lock newly mapped VMA with corrected ordering
Message-ID: <b5a5626-2684-899d-874b-801e7974b17@google.com>
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Lockdep is certainly right to complain about
(&vma->vm_lock->lock){++++}-{3:3}, at: vma_start_write+0x2d/0x3f
               but task is already holding lock:
(&mapping->i_mmap_rwsem){+.+.}-{3:3}, at: mmap_region+0x4dc/0x6db
Invert those to the usual ordering.

Fixes: 33313a747e81 ("mm: lock newly mapped VMA which can be modified after it becomes visible")
Cc: stable@vger.kernel.org
Signed-off-by: Hugh Dickins <hughd@google.com>
---
 mm/mmap.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 84c71431a527..3eda23c9ebe7 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2809,11 +2809,11 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 	if (vma_iter_prealloc(&vmi))
 		goto close_and_free_vma;
 
+	/* Lock the VMA since it is modified after insertion into VMA tree */
+	vma_start_write(vma);
 	if (vma->vm_file)
 		i_mmap_lock_write(vma->vm_file->f_mapping);
 
-	/* Lock the VMA since it is modified after insertion into VMA tree */
-	vma_start_write(vma);
 	vma_iter_store(&vmi, vma);
 	mm->map_count++;
 	if (vma->vm_file) {
-- 
2.35.3