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To: Andrew Morton Cc: Paul Menzel , Alexander Potapenko , Dmitry Vyukov , kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, Matthew Wilcox References: <12c9e499-9c11-d248-6a3f-14ec8c4e07f1@molgen.mpg.de> <20180201163349.8700-1-aryabinin@virtuozzo.com> <4fc394ae-65e8-7c51-112a-81bee0fb8429@virtuozzo.com> <20180522140305.5e0f8c62dcc2d735ed4ee84c@linux-foundation.org> From: Andrey Ryabinin Message-ID: Date: Wed, 23 May 2018 15:33:34 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180522140305.5e0f8c62dcc2d735ed4ee84c@linux-foundation.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [195.214.232.6] X-ClientProxiedBy: HE1PR0701CA0078.eurprd07.prod.outlook.com (2603:10a6:3:64::22) To VI1PR08MB3263.eurprd08.prod.outlook.com (2603:10a6:803:3d::18) X-MS-PublicTrafficType: Email X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(5600026)(4534165)(7168020)(4627221)(201703031133081)(201702281549075)(2017052603328)(7153060)(7193020);SRVR:VI1PR08MB3263; 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Use find_vm_area() to see if we can call vfree(). >>> >>> Unfortunately it's a bit tricky to properly unmap and free shadow allocated >>> during boot, so we'll have to keep it. If memory will come online again >>> that shadow will be reused. >>> >>> Fixes: fa69b5989bb0 ("mm/kasan: add support for memory hotplug") >>> Reported-by: Paul Menzel >>> Signed-off-by: Andrey Ryabinin >>> Cc: >>> --- >> >> This seems stuck in -mm. Andrew, can we proceed? > > OK. > > Should there be a code comment explaining the situation that Matthew > asked about? It's rather obscure. > Ok. Here is my attempt to improve the situation. If something is still not clear, I'm open to suggestions. From: Andrey Ryabinin Subject: [PATCH] mm-kasan-dont-vfree-nonexistent-vm_area-fix Improve comments. Signed-off-by: Andrey Ryabinin --- mm/kasan/kasan.c | 15 +++++++++++---- 1 file changed, 11 insertions(+), 4 deletions(-) diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c index 135ce2838c89..ea44dd0bc4e7 100644 --- a/mm/kasan/kasan.c +++ b/mm/kasan/kasan.c @@ -812,7 +812,7 @@ static bool shadow_mapped(unsigned long addr) /* * We can't use pud_large() or pud_huge(), the first one * is arch-specific, the last one depend on HUGETLB_PAGE. - * So let's abuse pud_bad(), if bud is bad it's has to + * So let's abuse pud_bad(), if pud is bad than it's bad * because it's huge. */ if (pud_bad(*pud)) @@ -871,9 +871,16 @@ static int __meminit kasan_mem_notifier(struct notifier_block *nb, struct vm_struct *vm; /* - * Only hot-added memory have vm_area. Freeing shadow - * mapped during boot would be tricky, so we'll just - * have to keep it. + * shadow_start was either mapped during boot by kasan_init() + * or during memory online by __vmalloc_node_range(). + * In the latter case we can use vfree() to free shadow. + * Non-NULL result of the find_vm_area() will tell us if + * that was the second case. + * + * Currently it's not possible to free shadow mapped + * during boot by kasan_init(). It's because the code + * to do that hasn't been written yet. So we'll just + * leak the memory. */ vm = find_vm_area((void *)shadow_start); if (vm) -- 2.16.1