[PATCH 4.9 047/177] IB/mlx4: Take write semaphore when changing the vma struct

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Maor Gottlieb <maorg@xxxxxxxxxxxx>


[ Upstream commit 22c3653d04bd0c67b75e99d85e0c0bdf83947df5 ]

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: ae184ddeca5db ('IB/mlx4_ib: Disassociate support')
Signed-off-by: Maor Gottlieb <maorg@xxxxxxxxxxxx>
Signed-off-by: Leon Romanovsky <leon@xxxxxxxxxx>
Signed-off-by: Doug Ledford <dledford@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/infiniband/hw/mlx4/main.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/infiniband/hw/mlx4/main.c
+++ b/drivers/infiniband/hw/mlx4/main.c
@@ -1168,7 +1168,7 @@ static void mlx4_ib_disassociate_ucontex
 	/* need to protect from a race on closing the vma as part of
 	 * mlx4_ib_vma_close().
 	 */
-	down_read(&owning_mm->mmap_sem);
+	down_write(&owning_mm->mmap_sem);
 	for (i = 0; i < HW_BAR_COUNT; i++) {
 		vma = context->hw_bar_info[i].vma;
 		if (!vma)
@@ -1186,7 +1186,7 @@ static void mlx4_ib_disassociate_ucontex
 		context->hw_bar_info[i].vma->vm_ops = NULL;
 	}
 
-	up_read(&owning_mm->mmap_sem);
+	up_write(&owning_mm->mmap_sem);
 	mmput(owning_mm);
 	put_task_struct(owning_process);
 }