Re: [PATCH RESEND rdma-rc] IB/core: Fix a nested dead lock as part of ODP flow

[Leon Romanovsky <leon@kernel.org>]

On Wed, Aug 24, 2022 at 09:10:36AM +0300, Leon Romanovsky wrote:
> From: Yishai Hadas <yishaih@nvidia.com>
> 
> Fix a nested dead lock as part of ODP flow by using mmput_async().
> 
> From the below call trace [1] can see that calling mmput() once we have
> the umem_odp->umem_mutex locked as required by
> ib_umem_odp_map_dma_and_lock() might trigger in the same task the
> exit_mmap()->__mmu_notifier_release()->mlx5_ib_invalidate_range() which
> may dead lock when trying to lock the same mutex.
> 
> Moving to use mmput_async() will solve the problem as the above
> exit_mmap() flow will be called in other task and will be executed once
> the lock will be available.
> 
> [1]
> [64843.077665] task:kworker/u133:2  state:D stack:    0 pid:80906 ppid:
> 2 flags:0x00004000
> [64843.077672] Workqueue: mlx5_ib_page_fault mlx5_ib_eqe_pf_action [mlx5_ib]
> [64843.077719] Call Trace:
> [64843.077722]  <TASK>
> [64843.077724]  __schedule+0x23d/0x590
> [64843.077729]  schedule+0x4e/0xb0
> [64843.077735]  schedule_preempt_disabled+0xe/0x10
> [64843.077740]  __mutex_lock.constprop.0+0x263/0x490
> [64843.077747]  __mutex_lock_slowpath+0x13/0x20
> [64843.077752]  mutex_lock+0x34/0x40
> [64843.077758]  mlx5_ib_invalidate_range+0x48/0x270 [mlx5_ib]
> [64843.077808]  __mmu_notifier_release+0x1a4/0x200
> [64843.077816]  exit_mmap+0x1bc/0x200
> [64843.077822]  ? walk_page_range+0x9c/0x120
> [64843.077828]  ? __cond_resched+0x1a/0x50
> [64843.077833]  ? mutex_lock+0x13/0x40
> [64843.077839]  ? uprobe_clear_state+0xac/0x120
> [64843.077860]  mmput+0x5f/0x140
> [64843.077867]  ib_umem_odp_map_dma_and_lock+0x21b/0x580 [ib_core]
> [64843.077931]  pagefault_real_mr+0x9a/0x140 [mlx5_ib]
> [64843.077962]  pagefault_mr+0xb4/0x550 [mlx5_ib]
> [64843.077992]  pagefault_single_data_segment.constprop.0+0x2ac/0x560
> [mlx5_ib]
> [64843.078022]  mlx5_ib_eqe_pf_action+0x528/0x780 [mlx5_ib]
> [64843.078051]  process_one_work+0x22b/0x3d0
> [64843.078059]  worker_thread+0x53/0x410
> [64843.078065]  ? process_one_work+0x3d0/0x3d0
> [64843.078073]  kthread+0x12a/0x150
> [64843.078079]  ? set_kthread_struct+0x50/0x50
> [64843.078085]  ret_from_fork+0x22/0x30
> [64843.078093]  </TASK>
> 
> Fixes: 36f30e486dce ("IB/core: Improve ODP to use hmm_range_fault()")
> Reviewed-by: Maor Gottlieb <maorg@nvidia.com>
> Signed-off-by: Yishai Hadas <yishaih@nvidia.com>
> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> ---
> Resend to larger forum.
> https://lore.kernel.org/all/74d93541ea533ef7daec6f126deb1072500aeb16.1661251841.git.leonro@nvidia.com
> ---
>  drivers/infiniband/core/umem_odp.c | 2 +-
>  kernel/fork.c                      | 1 +
>  2 files changed, 2 insertions(+), 1 deletion(-)

Any objections?

Thanks

> 
> diff --git a/drivers/infiniband/core/umem_odp.c b/drivers/infiniband/core/umem_odp.c
> index 186ed8859920..d39e16c211e8 100644
> --- a/drivers/infiniband/core/umem_odp.c
> +++ b/drivers/infiniband/core/umem_odp.c
> @@ -462,7 +462,7 @@ int ib_umem_odp_map_dma_and_lock(struct ib_umem_odp *umem_odp, u64 user_virt,
>  		mutex_unlock(&umem_odp->umem_mutex);
>  
>  out_put_mm:
> -	mmput(owning_mm);
> +	mmput_async(owning_mm);
>  out_put_task:
>  	if (owning_process)
>  		put_task_struct(owning_process);
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 90c85b17bf69..8a9e92068b15 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1225,6 +1225,7 @@ void mmput_async(struct mm_struct *mm)
>  		schedule_work(&mm->async_put_work);
>  	}
>  }
> +EXPORT_SYMBOL_GPL(mmput_async);
>  #endif
>  
>  /**
> -- 
> 2.37.2
>