[PATCH AUTOSEL for 4.9 066/190] IB/mlx5: Take write semaphore when changing the vma struct

[Sasha Levin]

From: Maor Gottlieb <ma...@mellanox.com>

[ Upstream commit ecc7d83be3243835c9396a1a2fb8ce95f205207b ]

When the driver disassociate user context, it changes the vma to
anonymous by setting the vm_ops to null and zap the vma ptes.

In order to avoid race in the kernel, we need to take write lock
before we change the vma entries.

Fixes: 7c2344c3bbf97 ('IB/mlx5: Implements disassociate_ucontext API')
Signed-off-by: Maor Gottlieb <ma...@mellanox.com>
Signed-off-by: Leon Romanovsky <l...@kernel.org>
Signed-off-by: Doug Ledford <dledf...@redhat.com>
Signed-off-by: Sasha Levin <alexander.le...@microsoft.com>
---
 drivers/infiniband/hw/mlx5/main.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/infiniband/hw/mlx5/main.c 
b/drivers/infiniband/hw/mlx5/main.c
index 5e29fbd3a5a0..150227786969 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -1313,7 +1313,7 @@ static void mlx5_ib_disassociate_ucontext(struct 
ib_ucontext *ibcontext)
        /* need to protect from a race on closing the vma as part of
         * mlx5_ib_vma_close.
         */
-       down_read(&owning_mm->mmap_sem);
+       down_write(&owning_mm->mmap_sem);
        list_for_each_entry_safe(vma_private, n, &context->vma_private_list,
                                 list) {
                vma = vma_private->vma;
@@ -1327,7 +1327,7 @@ static void mlx5_ib_disassociate_ucontext(struct 
ib_ucontext *ibcontext)
                list_del(&vma_private->list);
                kfree(vma_private);
        }
-       up_read(&owning_mm->mmap_sem);
+       up_write(&owning_mm->mmap_sem);
        mmput(owning_mm);
        put_task_struct(owning_process);
 }
-- 
2.14.1