2024-03-21 23:59:00

by Lokesh Gidra

Subject: [PATCH] userfaultfd: fix deadlock warning when locking src and dst VMAs

Use down_read_nested() to avoid the warning.

Reported-by: [email protected]
Signed-off-by: Lokesh Gidra <[email protected]>
---
mm/userfaultfd.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 712160cd41ec..3c3539c573e7 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1444,7 +1444,8 @@ static int uffd_move_lock(struct mm_struct *mm,
*/
down_read(&(*dst_vmap)->vm_lock->lock);
if (*dst_vmap != *src_vmap)
- down_read(&(*src_vmap)->vm_lock->lock);
+ down_read_nested(&(*src_vmap)->vm_lock->lock,
+ SINGLE_DEPTH_NESTING);
}
mmap_read_unlock(mm);
return err;
--
2.44.0.396.g6e790dbe36-goog

2024-03-22 00:51:45

by Andrew Morton

Subject: Re: [PATCH] userfaultfd: fix deadlock warning when locking src and dst VMAs

On Thu, 21 Mar 2024 16:58:18 -0700 Lokesh Gidra <[email protected]> wrote:

> Use down_read_nested() to avoid the warning.
>
> --- a/mm/userfaultfd.c
> +++ b/mm/userfaultfd.c
> @@ -1444,7 +1444,8 @@ static int uffd_move_lock(struct mm_struct *mm,
> */
> down_read(&(*dst_vmap)->vm_lock->lock);
> if (*dst_vmap != *src_vmap)
> - down_read(&(*src_vmap)->vm_lock->lock);
> + down_read_nested(&(*src_vmap)->vm_lock->lock,
> + SINGLE_DEPTH_NESTING);
> }
> mmap_read_unlock(mm);
> return err;

Thanks, I added

Fixes: 867a43a34ff8a ("userfaultfd: use per-vma locks in userfaultfd operations")