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


> -----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

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