[PATCH v3 2/2][v4.9.y] coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping

[Ajay Kaher]

This patch is the extension of following upstream commit to fix
the race condition between get_task_mm() and core dumping
for IB->mlx4 and IB->mlx5 drivers:

commit 04f5866e41fb ("coredump: fix race condition between
mmget_not_zero()/get_task_mm() and core dumping")'

Thanks to Jason for pointing this.

Signed-off-by: Ajay Kaher <aka...@vmware.com>
---
 drivers/infiniband/hw/mlx4/main.c | 4 +++-
 drivers/infiniband/hw/mlx5/main.c | 3 +++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/hw/mlx4/main.c 
b/drivers/infiniband/hw/mlx4/main.c
index 8d59a59..7ccf722 100644
--- a/drivers/infiniband/hw/mlx4/main.c
+++ b/drivers/infiniband/hw/mlx4/main.c
@@ -1172,6 +1172,8 @@ static void mlx4_ib_disassociate_ucontext(struct 
ib_ucontext *ibcontext)
         * mlx4_ib_vma_close().
         */
        down_write(&owning_mm->mmap_sem);
+       if (!mmget_still_valid(owning_mm))
+               goto skip_mm;
        for (i = 0; i < HW_BAR_COUNT; i++) {
                vma = context->hw_bar_info[i].vma;
                if (!vma)
@@ -1190,7 +1192,7 @@ static void mlx4_ib_disassociate_ucontext(struct 
ib_ucontext *ibcontext)
                /* context going to be destroyed, should not access ops any 
more */
                context->hw_bar_info[i].vma->vm_ops = NULL;
        }
-
+skip_mm:
        up_write(&owning_mm->mmap_sem);
        mmput(owning_mm);
        put_task_struct(owning_process);
diff --git a/drivers/infiniband/hw/mlx5/main.c 
b/drivers/infiniband/hw/mlx5/main.c
index b1daf5c..f94df0e 100644
--- a/drivers/infiniband/hw/mlx5/main.c
+++ b/drivers/infiniband/hw/mlx5/main.c
@@ -1307,6 +1307,8 @@ static void mlx5_ib_disassociate_ucontext(struct 
ib_ucontext *ibcontext)
         * mlx5_ib_vma_close.
         */
        down_write(&owning_mm->mmap_sem);
+       if (!mmget_still_valid(owning_mm))
+               goto skip_mm;
        list_for_each_entry_safe(vma_private, n, &context->vma_private_list,
                                 list) {
                vma = vma_private->vma;
@@ -1321,6 +1323,7 @@ static void mlx5_ib_disassociate_ucontext(struct 
ib_ucontext *ibcontext)
                list_del(&vma_private->list);
                kfree(vma_private);
        }
+skip_mm:
        up_write(&owning_mm->mmap_sem);
        mmput(owning_mm);
        put_task_struct(owning_process);
-- 
2.7.4