RE: [PATCH] cma: don't quit at first error when activating reserved areas

["Song Bao Hua (Barry Song)" <song.bao.hua@hisilicon.com>]

> -----Original Message-----
> From: Mike Kravetz [mailto:mike.kravetz@oracle.com]
> Sent: Friday, July 31, 2020 4:31 AM
> To: linux-mm@kvack.org; linux-kernel@vger.kernel.org
> Cc: Marek Szyprowski <m.szyprowski@samsung.com>; Michal Nazarewicz
> <mina86@mina86.com>; Kyungmin Park <kyungmin.park@samsung.com>;
> Song Bao Hua (Barry Song) <song.bao.hua@hisilicon.com>; Roman Gushchin
> <guro@fb.com>; Andrew Morton <akpm@linux-foundation.org>; Mike Kravetz
> <mike.kravetz@oracle.com>; stable@vger.kernel.org
> Subject: [PATCH] cma: don't quit at first error when activating reserved areas
> 
> The routine cma_init_reserved_areas is designed to activate all reserved cma
> areas.  It quits when it first encounters an error.
> This can leave some areas in a state where they are reserved but not activated.
> There is no feedback to code which performed the reservation.  Attempting to
> allocate memory from areas in such a state will result in a BUG.
> 
> Modify cma_init_reserved_areas to always attempt to activate all areas.  The
> called routine, cma_activate_area is responsible for leaving the area in a valid
> state.  No one is making active use of returned error codes, so change the
> routine to void.
> 
> How to reproduce:  This example uses kernelcore, hugetlb and cma as an easy
> way to reproduce.  However, this is a more general cma issue.
> 
> Two node x86 VM 16GB total, 8GB per node Kernel command line parameters,
> kernelcore=4G hugetlb_cma=8G Related boot time messages,
>   hugetlb_cma: reserve 8192 MiB, up to 4096 MiB per node
>   cma: Reserved 4096 MiB at 0x0000000100000000
>   hugetlb_cma: reserved 4096 MiB on node 0
>   cma: Reserved 4096 MiB at 0x0000000300000000
>   hugetlb_cma: reserved 4096 MiB on node 1
>   cma: CMA area hugetlb could not be activated
> 
>  # echo 8 > /sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
> 
>   BUG: kernel NULL pointer dereference, address: 0000000000000000
>   #PF: supervisor read access in kernel mode
>   #PF: error_code(0x0000) - not-present page
>   PGD 0 P4D 0
>   Oops: 0000 [#1] SMP PTI
>   ...
>   Call Trace:
>     bitmap_find_next_zero_area_off+0x51/0x90
>     cma_alloc+0x1a5/0x310
>     alloc_fresh_huge_page+0x78/0x1a0
>     alloc_pool_huge_page+0x6f/0xf0
>     set_max_huge_pages+0x10c/0x250
>     nr_hugepages_store_common+0x92/0x120
>     ? __kmalloc+0x171/0x270
>     kernfs_fop_write+0xc1/0x1a0
>     vfs_write+0xc7/0x1f0
>     ksys_write+0x5f/0xe0
>     do_syscall_64+0x4d/0x90
>     entry_SYSCALL_64_after_hwframe+0x44/0xa9
> 
> Fixes: c64be2bb1c6e ("drivers: add Contiguous Memory Allocator")
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: <stable@vger.kernel.org>

Acked-by: Barry Song <song.bao.hua@hisilicon.com>

> ---
>  mm/cma.c | 23 +++++++++--------------
>  1 file changed, 9 insertions(+), 14 deletions(-)
> 
> diff --git a/mm/cma.c b/mm/cma.c
> index 26ecff818881..0963c0f9c502 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -93,17 +93,15 @@ static void cma_clear_bitmap(struct cma *cma,
> unsigned long pfn,
>  	mutex_unlock(&cma->lock);
>  }
> 
> -static int __init cma_activate_area(struct cma *cma)
> +static void __init cma_activate_area(struct cma *cma)
>  {
>  	unsigned long base_pfn = cma->base_pfn, pfn = base_pfn;
>  	unsigned i = cma->count >> pageblock_order;
>  	struct zone *zone;
> 
>  	cma->bitmap = bitmap_zalloc(cma_bitmap_maxno(cma), GFP_KERNEL);
> -	if (!cma->bitmap) {
> -		cma->count = 0;
> -		return -ENOMEM;
> -	}
> +	if (!cma->bitmap)
> +		goto out_error;
> 
>  	WARN_ON_ONCE(!pfn_valid(pfn));
>  	zone = page_zone(pfn_to_page(pfn));
> @@ -133,25 +131,22 @@ static int __init cma_activate_area(struct cma
> *cma)
>  	spin_lock_init(&cma->mem_head_lock);
>  #endif
> 
> -	return 0;
> +	return;
> 
>  not_in_zone:
> -	pr_err("CMA area %s could not be activated\n", cma->name);
>  	bitmap_free(cma->bitmap);
> +out_error:
>  	cma->count = 0;
> -	return -EINVAL;
> +	pr_err("CMA area %s could not be activated\n", cma->name);
> +	return;
>  }
> 
>  static int __init cma_init_reserved_areas(void)  {
>  	int i;
> 
> -	for (i = 0; i < cma_area_count; i++) {
> -		int ret = cma_activate_area(&cma_areas[i]);
> -
> -		if (ret)
> -			return ret;
> -	}
> +	for (i = 0; i < cma_area_count; i++)
> +		cma_activate_area(&cma_areas[i]);
> 
>  	return 0;
>  }
> --
> 2.25.4