linux-kernel - [PATCH] hugetlbfs: skip VMAs without shareable locks in hugetlb_vmdelete

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Message-ID: <20250925143312.149623-1-kartikey406@gmail.com>
Date: Thu, 25 Sep 2025 20:03:09 +0530
From: Deepanshu Kartikey <kartikey406@...il.com>
To: muchun.song@...ux.dev,
	osalvador@...e.de,
	david@...hat.com
Cc: akpm@...ux-foundation.org,
	mike.kravetz@...cle.com,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Deepanshu Kartikey <kartikey406@...il.com>,
	syzbot+f26d7c75c26ec19790e7@...kaller.appspotmail.com
Subject: [PATCH] hugetlbfs: skip VMAs without shareable locks in hugetlb_vmdelete_list

hugetlb_vmdelete_list() uses trylock to acquire VMA locks during truncate
operations. As per the original design in commit 40549ba8f8e0 ("hugetlb:
use new vma_lock for pmd sharing synchronization"), if the trylock fails
or the VMA has no lock, it should skip that VMA. Any remaining mapped
pages are handled by remove_inode_hugepages() which is called after
hugetlb_vmdelete_list() and uses proper lock ordering to guarantee
unmapping success.

Currently, when hugetlb_vma_trylock_write() returns success (1) for VMAs
without shareable locks, the code proceeds to call unmap_hugepage_range().
This causes assertion failures in huge_pmd_unshare() → hugetlb_vma_assert_locked()
because no lock is actually held:

  WARNING: CPU: 1 PID: 6594 Comm: syz.0.28 Not tainted
  Call Trace:
   hugetlb_vma_assert_locked+0x1dd/0x250
   huge_pmd_unshare+0x2c8/0x540
   __unmap_hugepage_range+0x6e3/0x1aa0
   unmap_hugepage_range+0x32e/0x410
   hugetlb_vmdelete_list+0x189/0x1f0

Fix by explicitly skipping VMAs without shareable locks after trylock
succeeds, consistent with the original design where such VMAs are
deferred to remove_inode_hugepages() for proper handling.

Reported-by: syzbot+f26d7c75c26ec19790e7@...kaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=f26d7c75c26ec19790e7
Fixes: 40549ba8f8e0 ("hugetlb: use new vma_lock for pmd sharing synchronization")
Tested-by: syzbot+f26d7c75c26ec19790e7@...kaller.appspotmail.com
Signed-off-by: Deepanshu Kartikey <kartikey406@...il.com>
---
 fs/hugetlbfs/inode.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 9e0625167517..9ba98cab3388 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -487,7 +487,8 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end,

 		if (!hugetlb_vma_trylock_write(vma))
 			continue;
-
+		if (!__vma_shareable_lock(vma))
+			continue;
 		v_start = vma_offset_start(vma, start);
 		v_end = vma_offset_end(vma, end);

-- 
2.43.0