Re: [PATCH 5.15 04/42] RDMA/mlx5: Fix releasing unallocated memory in dereg MR flow

[Thorsten Leemhuis <regressions@leemhuis.info>]

Hi, this is your Linux kernel regression tracker speaking.

On 15.12.21 18:20, Greg Kroah-Hartman wrote:
> From: Alaa Hleihel <alaa@nvidia.com>
> 
> [ Upstream commit f0ae4afe3d35e67db042c58a52909e06262b740f ]
> 
> For the case of IB_MR_TYPE_DM the mr does doesn't have a umem, even though
> it is a user MR. This causes function mlx5_free_priv_descs() to think that
> it is a kernel MR, leading to wrongly accessing mr->descs that will get
> wrong values in the union which leads to attempt to release resources that
> were not allocated in the first place.

TWIMC, that commit made it into 5.15.y, but is known to cause a
regression in v5.16-rc:

https://lore.kernel.org/lkml/f298db4ec5fdf7a2d1d166ca2f66020fd9397e5c.1640079962.git.leonro@nvidia.com/
https://lore.kernel.org/all/EEBA2D1C-F29C-4237-901C-587B60CEE113@oracle.com/

A fix for mainline was posted, but got stuck afaics:
https://lore.kernel.org/lkml/f298db4ec5fdf7a2d1d166ca2f66020fd9397e5c.1640079962.git.leonro@nvidia.com/

A revert was also discussed, but not performed:
https://lore.kernel.org/all/20211222101312.1358616-1-maorg@nvidia.com/

Ciao, Thorsten

> For example:
>  DMA-API: mlx5_core 0000:08:00.1: device driver tries to free DMA memory it has not allocated [device address=0x0000000000000000] [size=0 bytes]
>  WARNING: CPU: 8 PID: 1021 at kernel/dma/debug.c:961 check_unmap+0x54f/0x8b0
>  RIP: 0010:check_unmap+0x54f/0x8b0
>  Call Trace:
>   debug_dma_unmap_page+0x57/0x60
>   mlx5_free_priv_descs+0x57/0x70 [mlx5_ib]
>   mlx5_ib_dereg_mr+0x1fb/0x3d0 [mlx5_ib]
>   ib_dereg_mr_user+0x60/0x140 [ib_core]
>   uverbs_destroy_uobject+0x59/0x210 [ib_uverbs]
>   uobj_destroy+0x3f/0x80 [ib_uverbs]
>   ib_uverbs_cmd_verbs+0x435/0xd10 [ib_uverbs]
>   ? uverbs_finalize_object+0x50/0x50 [ib_uverbs]
>   ? lock_acquire+0xc4/0x2e0
>   ? lock_acquired+0x12/0x380
>   ? lock_acquire+0xc4/0x2e0
>   ? lock_acquire+0xc4/0x2e0
>   ? ib_uverbs_ioctl+0x7c/0x140 [ib_uverbs]
>   ? lock_release+0x28a/0x400
>   ib_uverbs_ioctl+0xc0/0x140 [ib_uverbs]
>   ? ib_uverbs_ioctl+0x7c/0x140 [ib_uverbs]
>   __x64_sys_ioctl+0x7f/0xb0
>   do_syscall_64+0x38/0x90
> 
> Fix it by reorganizing the dereg flow and mlx5_ib_mr structure:
>  - Move the ib_umem field into the user MRs structure in the union as it's
>    applicable only there.
>  - Function mlx5_ib_dereg_mr() will now call mlx5_free_priv_descs() only
>    in case there isn't udata, which indicates that this isn't a user MR.
> 
> Fixes: f18ec4223117 ("RDMA/mlx5: Use a union inside mlx5_ib_mr")
> Link: https://lore.kernel.org/r/66bb1dd253c1fd7ceaa9fc411061eefa457b86fb.1637581144.git.leonro@nvidia.com
> Signed-off-by: Alaa Hleihel <alaa@nvidia.com>
> Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
>  drivers/infiniband/hw/mlx5/mlx5_ib.h |  6 +++---
>  drivers/infiniband/hw/mlx5/mr.c      | 26 ++++++++++++--------------
>  2 files changed, 15 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/infiniband/hw/mlx5/mlx5_ib.h b/drivers/infiniband/hw/mlx5/mlx5_ib.h
> index bf20a388eabe1..6204ae2caef58 100644
> --- a/drivers/infiniband/hw/mlx5/mlx5_ib.h
> +++ b/drivers/infiniband/hw/mlx5/mlx5_ib.h
> @@ -641,7 +641,6 @@ struct mlx5_ib_mr {
>  
>  	/* User MR data */
>  	struct mlx5_cache_ent *cache_ent;
> -	struct ib_umem *umem;
>  
>  	/* This is zero'd when the MR is allocated */
>  	union {
> @@ -653,7 +652,7 @@ struct mlx5_ib_mr {
>  			struct list_head list;
>  		};
>  
> -		/* Used only by kernel MRs (umem == NULL) */
> +		/* Used only by kernel MRs */
>  		struct {
>  			void *descs;
>  			void *descs_alloc;
> @@ -675,8 +674,9 @@ struct mlx5_ib_mr {
>  			int data_length;
>  		};
>  
> -		/* Used only by User MRs (umem != NULL) */
> +		/* Used only by User MRs */
>  		struct {
> +			struct ib_umem *umem;
>  			unsigned int page_shift;
>  			/* Current access_flags */
>  			int access_flags;
> diff --git a/drivers/infiniband/hw/mlx5/mr.c b/drivers/infiniband/hw/mlx5/mr.c
> index 22e2f4d79743d..69b2ce4c292ae 100644
> --- a/drivers/infiniband/hw/mlx5/mr.c
> +++ b/drivers/infiniband/hw/mlx5/mr.c
> @@ -1911,19 +1911,18 @@ mlx5_alloc_priv_descs(struct ib_device *device,
>  	return ret;
>  }
>  
> -static void
> -mlx5_free_priv_descs(struct mlx5_ib_mr *mr)
> +static void mlx5_free_priv_descs(struct mlx5_ib_mr *mr)
>  {
> -	if (!mr->umem && mr->descs) {
> -		struct ib_device *device = mr->ibmr.device;
> -		int size = mr->max_descs * mr->desc_size;
> -		struct mlx5_ib_dev *dev = to_mdev(device);
> +	struct mlx5_ib_dev *dev = to_mdev(mr->ibmr.device);
> +	int size = mr->max_descs * mr->desc_size;
>  
> -		dma_unmap_single(&dev->mdev->pdev->dev, mr->desc_map, size,
> -				 DMA_TO_DEVICE);
> -		kfree(mr->descs_alloc);
> -		mr->descs = NULL;
> -	}
> +	if (!mr->descs)
> +		return;
> +
> +	dma_unmap_single(&dev->mdev->pdev->dev, mr->desc_map, size,
> +			 DMA_TO_DEVICE);
> +	kfree(mr->descs_alloc);
> +	mr->descs = NULL;
>  }
>  
>  int mlx5_ib_dereg_mr(struct ib_mr *ibmr, struct ib_udata *udata)
> @@ -1999,7 +1998,8 @@ int mlx5_ib_dereg_mr(struct ib_mr *ibmr, struct ib_udata *udata)
>  	if (mr->cache_ent) {
>  		mlx5_mr_cache_free(dev, mr);
>  	} else {
> -		mlx5_free_priv_descs(mr);
> +		if (!udata)
> +			mlx5_free_priv_descs(mr);
>  		kfree(mr);
>  	}
>  	return 0;
> @@ -2086,7 +2086,6 @@ static struct mlx5_ib_mr *mlx5_ib_alloc_pi_mr(struct ib_pd *pd,
>  	if (err)
>  		goto err_free_in;
>  
> -	mr->umem = NULL;
>  	kfree(in);
>  
>  	return mr;
> @@ -2213,7 +2212,6 @@ static struct ib_mr *__mlx5_ib_alloc_mr(struct ib_pd *pd,
>  	}
>  
>  	mr->ibmr.device = pd->device;
> -	mr->umem = NULL;
>  
>  	switch (mr_type) {
>  	case IB_MR_TYPE_MEM_REG: