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Wed, 6 Mar 2024 15:58:31 +0800 Subject: Re: [PATCH 0/5] Remove some races around folio_test_hugetlb To: Matthew Wilcox CC: Oscar Salvador , Linux-MM References: <20240301214712.2853147-1-willy@infradead.org> From: Miaohe Lin Message-ID: <82f585d5-052e-075d-0a08-fbf6e672d42c@huawei.com> Date: Wed, 6 Mar 2024 15:58:31 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.173.135.154] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To canpemm500002.china.huawei.com (7.192.104.244) X-Rspamd-Queue-Id: 19B5740006 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: knkjxn8zat37basay738gfrw1y5ghwgp X-HE-Tag: 1709711916-204360 X-HE-Meta: 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 yOalljB+ rCGrAWsOCSrsooiF8D3swm5uKc/nOgcHLmNEVMBcQIydRes72kKxJ+7p0O9sv4OmhgvpLBH+n2jA6QXb9wJoBh3lAQDsbvb4VLw9FTfhrXwQqC4wyrC2ZQ4/ln94jxdh7wq9zqH4GGrm1E9Zp6f/jUDds9bwP4sruJfgesmjcNKQKZzI/U7L2u5Oc8y7IDQhYWI+c1mwd1Xx4cJCrhDXvMvNRFCRDOWuHAqtCalfpD9Kvim0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2024/3/5 1:08, Matthew Wilcox wrote: > On Mon, Mar 04, 2024 at 05:09:58PM +0800, Miaohe Lin wrote: >> I encountered similar issues with PageSwapCache check when doing memory-failure test: >> >> [66258.945079] page:00000000135e1205 refcount:1 mapcount:0 mapping:0000000000000000 index:0x9b pfn:0xa04e9a >> [66258.949096] head:0000000038449724 order:9 entire_mapcount:1 nr_pages_mapped:0 pincount:0 >> [66258.949485] memcg:ffff95fb43379000 >> [66258.950334] anon flags: 0x6fffc00000a0068(uptodate|lru|head|mappedtodisk|swapbacked|node=1|zone=2|lastcpupid=0x3fff) >> [66258.951212] page_type: 0xffffffff() >> [66258.951882] raw: 06fffc0000000000 ffffc89628138001 dead000000000122 dead000000000400 >> [66258.952273] raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000 >> [66258.952884] head: 06fffc00000a0068 ffffc896218a8008 ffffc89621680008 ffff95fb4349c439 >> [66258.953239] head: 0000000700000600 0000000000000000 00000001ffffffff ffff95fb43379000 >> [66258.953725] page dumped because: VM_BUG_ON_PAGE(PageTail(page)) >> [66258.954497] ------------[ cut here ]------------ >> [66258.954937] kernel BUG at include/linux/page-flags.h:313! >> [66258.956502] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI >> [66258.957001] CPU: 14 PID: 174237 Comm: page-types Kdump: loaded Not tainted 6.8.0-rc1-00162-gd162e170f118 #11 >> [66258.957001] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014 >> [66258.958415] RIP: 0010:folio_flags.constprop.0+0x1c/0x50 >> [66258.958415] Code: 90 90 90 90 90 90 90 90 90 90 90 90 90 90 48 8b 57 08 48 89 f8 83 e2 01 74 12 48 c7 c6 a0 59 34 a7 48 89 c7 e8 b5 60 e8 ff 90 <0f> 0b 66 90 c3 cc cc cc cc f7 c7 ff 0f 00 00 75 1a 48 8b 17 83 e2 >> [66258.958415] RSP: 0018:ffffa0f38ae53e00 EFLAGS: 00000282 >> [66258.958415] RAX: 0000000000000033 RBX: 0000000000000000 RCX: ffff96031fd9c9c8 >> [66258.958415] RDX: 0000000000000000 RSI: 0000000000000027 RDI: ffff96031fd9c9c0 >> [66258.958415] RBP: ffffc8962813a680 R08: ffffffffa7756f88 R09: 0000000000009ffb >> [66258.962155] R10: 000000000000054a R11: ffffffffa7726fa0 R12: 06fffc0000000000 >> [66258.962155] R13: 0000000000000000 R14: 00007fff93bf1348 R15: 0000000000a04e9a >> [66258.962155] FS: 00007f47cc5c4740(0000) GS:ffff96031fd80000(0000) knlGS:0000000000000000 >> [66258.962155] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 >> [66258.962155] CR2: 00007fff93c7b000 CR3: 0000000850c28000 CR4: 00000000000006f0 >> [66258.962155] Call Trace: >> [66258.962155] >> [66258.965730] stable_page_flags+0x210/0x940 >> [66258.965730] kpageflags_read+0x97/0xf0 > > Clearly nobody has loved kpageflags_read() in a long time. It's > absolutely full of bugs, some harmless, others less so. > > The heart of the problem is that nobody has a refcount on the page, so > literally everything can change under us. The old implementations of > PageSwapCache (etc) would silently give bad information; the folio > reimplementations warn you when you hit this race. > > We have a few options: > > - We could grab a reference. That would probaby be unwelcome. > - We can grab a snapshot. Might be a bit overkill. > - We can grab the parts of the page/folio we need and open-code our > tests. This actually seems easiest. Option 3 should be the easiest way to fix the issue though it seems the code would be slightly ugly. Will you send a formal patch? Thanks Matthew!