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] <TASK> >> [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!
