Re: [PATCH V2] iommu/iova: Init the struct iova to fix the possible memleak

[Robin Murphy]

On 09/12/2019 8:24 am, Xiaotao Yin wrote:
> During ethernet(Marvell octeontx2) set ring buffer test:
> ethtool -G eth1 rx <rx ring size> tx <tx ring size>
> following kmemleak will happen sometimes:
>
> unreferenced object 0xffff000b85421340 (size 64):
>    comm "ethtool", pid 867, jiffies 4295323539 (age 550.500s)
>    hex dump (first 64 bytes):
>      80 13 42 85 0b 00 ff ff ff ff ff ff ff ff ff ff  ..B.............
>      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>      ff ff ff ff ff ff ff ff 00 00 00 00 00 00 00 00  ................
>      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>    backtrace:
>      [<000000001b204ddf>] kmem_cache_alloc+0x1b0/0x350
>      [<00000000d9ef2e50>] alloc_iova+0x3c/0x168
>      [<00000000ea30f99d>] alloc_iova_fast+0x7c/0x2d8
>      [<00000000b8bb2f1f>] iommu_dma_alloc_iova.isra.0+0x12c/0x138
>      [<000000002f1a43b5>] __iommu_dma_map+0x8c/0xf8
>      [<00000000ecde7899>] iommu_dma_map_page+0x98/0xf8
>      [<0000000082004e59>] otx2_alloc_rbuf+0xf4/0x158
>      [<000000002b107f6b>] otx2_rq_aura_pool_init+0x110/0x270
>      [<00000000c3d563c7>] otx2_open+0x15c/0x734
>      [<00000000a2f5f3a8>] otx2_dev_open+0x3c/0x68
>      [<00000000456a98b5>] otx2_set_ringparam+0x1ac/0x1d4
>      [<00000000f2fbb819>] dev_ethtool+0xb84/0x2028
>      [<0000000069b67c5a>] dev_ioctl+0x248/0x3a0
>      [<00000000af38663a>] sock_ioctl+0x280/0x638
>      [<000000002582384c>] do_vfs_ioctl+0x8b0/0xa80
>      [<000000004e1a2c02>] ksys_ioctl+0x84/0xb8
>
> The reason:
> When alloc_iova_mem() without initial with Zero, sometimes fpn_lo will equal to
> IOVA_ANCHOR by chance, so when return from __alloc_and_insert_iova_range() with
> -ENOMEM(iova32_full), the new_iova will not be freed in free_iova_mem().

Ooh, subtle... nice catch!

I suppose we could also open-code the kmem_cache_free() call in 
alloc_iova() to bypass the check entirely because "we know what we're 
doing", but only if the zeroing proves to have a measurable overhead.

> Fixes: bb68b2fbfbd6 ("iommu/iova: Add rbtree anchor node")
> Signed-off-by: Xiaotao Yin <xiaotao.yin@xxxxxxxxxxxxx>
> ---
>   drivers/iommu/iova.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c
> index 41c605b0058f..2c27a661632c 100644
> --- a/drivers/iommu/iova.c
> +++ b/drivers/iommu/iova.c
> @@ -233,7 +233,7 @@ static DEFINE_MUTEX(iova_cache_mutex);
>   
>   struct iova *alloc_iova_mem(void)
>   {
> -	return kmem_cache_alloc(iova_cache, GFP_ATOMIC);
> +	return kmem_cache_alloc(iova_cache, GFP_ATOMIC | __GFP_ZERO);

FWIW there is a kmem_cache_zalloc() helper, which seems fairly 
well-established. Either way, though,

Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>

>   }
>   EXPORT_SYMBOL(alloc_iova_mem);
>