From faf3c923523e5c8fc3baaa413d62e913774ae52f Mon Sep 17 00:00:00 2001 From: "Matthew Wilcox (Oracle)" Date: Fri, 28 Nov 2025 04:00:58 +0000 Subject: [PATCH] mm: fix vma_start_write_killable() signal handling If we get a signal, we need to restore the vm_refcnt. We don't think that the refcount can actually be decremented to zero here as it requires the VMA to be detached, and the vma_mark_detached() uses TASK_UNINTERRUPTIBLE. However, that's a bit subtle, so handle it as if the refcount was zero at the start of this function. Link: https://lkml.kernel.org/r/20251128040100.3022561-1-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) Reported-by: syzbot+5b19bad23ac7f44bf8b8@syzkaller.appspotmail.com Fixes: 2197bb60f890 ("mm: add vma_start_write_killable()") Reviewed-by: Suren Baghdasaryan Reviewed-by: Vlastimil Babka Reviewed-by: Lorenzo Stoakes Reviewed-by: Liam R. Howlett Signed-off-by: Andrew Morton --- mm/mmap_lock.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c index e6e5570d1ec7..7421b7ea8001 100644 --- a/mm/mmap_lock.c +++ b/mm/mmap_lock.c @@ -74,6 +74,14 @@ static inline int __vma_enter_locked(struct vm_area_struct *vma, refcount_read(&vma->vm_refcnt) == tgt_refcnt, state); if (err) { + if (refcount_sub_and_test(VMA_LOCK_OFFSET, &vma->vm_refcnt)) { + /* + * The wait failed, but the last reader went away + * as well. Tell the caller the VMA is detached. + */ + WARN_ON_ONCE(!detaching); + err = 0; + } rwsem_release(&vma->vmlock_dep_map, _RET_IP_); return err; }