On Fri 26-07-19 06:25:49, Toshiki Fukasawa wrote: > > > On 2019/07/25 18:03, Michal Hocko wrote: > > On Thu 25-07-19 02:31:18, Toshiki Fukasawa wrote: > >> A kernel panic was observed during reading /proc/kpageflags for > >> first few pfns allocated by pmem namespace: > >> > >> BUG: unable to handle page fault for address: fffffffffffffffe > >> [ 114.495280] #PF: supervisor read access in kernel mode > >> [ 114.495738] #PF: error_code(0x0000) - not-present page > >> [ 114.496203] PGD 17120e067 P4D 17120e067 PUD 171210067 PMD 0 > >> [ 114.496713] Oops: 0000 [#1] SMP PTI > >> [ 114.497037] CPU: 9 PID: 1202 Comm: page-types Not tainted 5.3.0-rc1 #1 > >> [ 114.497621] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS > >> rel-1.11.0-0-g63451fca13-prebuilt.qemu-project.org 04/01/2014 > >> [ 114.498706] RIP: 0010:stable_page_flags+0x27/0x3f0 > >> [ 114.499142] Code: 82 66 90 66 66 66 66 90 48 85 ff 0f 84 d1 03 00 00 41 > >> 54 55 48 89 fd 53 48 8b 57 08 48 8b 1f 48 8d 42 ff 83 e2 01 48 0f 44 c7 > >> <48> 8b 00 f6 c4 02 0f 84 57 03 00 00 45 31 e4 48 8b 55 08 48 89 ef > >> [ 114.500788] RSP: 0018:ffffa5e601a0fe60 EFLAGS: 00010202 > >> [ 114.501373] RAX: fffffffffffffffe RBX: ffffffffffffffff RCX: > >> 0000000000000000 > >> [ 114.502009] RDX: 0000000000000001 RSI: 00007ffca13a7310 RDI: > >> ffffd07489000000 > >> [ 114.502637] RBP: ffffd07489000000 R08: 0000000000000001 R09: > >> 0000000000000000 > >> [ 114.503270] R10: 0000000000000000 R11: 0000000000000000 R12: > >> 0000000000240000 > >> [ 114.503896] R13: 0000000000080000 R14: 00007ffca13a7310 R15: > >> ffffa5e601a0ff08 > >> [ 114.504530] FS: 00007f0266c7f540(0000) GS:ffff962dbbac0000(0000) > >> knlGS:0000000000000000 > >> [ 114.505245] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > >> [ 114.505754] CR2: fffffffffffffffe CR3: 000000023a204000 CR4: > >> 00000000000006e0 > >> [ 114.506401] Call Trace: > >> [ 114.506660] kpageflags_read+0xb1/0x130 > >> [ 114.507051] proc_reg_read+0x39/0x60 > >> [ 114.507387] vfs_read+0x8a/0x140 > >> [ 114.507686] ksys_pread64+0x61/0xa0 > >> [ 114.508021] do_syscall_64+0x5f/0x1a0 > >> [ 114.508372] entry_SYSCALL_64_after_hwframe+0x44/0xa9 > >> [ 114.508844] RIP: 0033:0x7f0266ba426b > >> > >> The reason for the panic is that stable_page_flags() which parses > >> the page flags uses uninitialized struct pages reserved by the > >> ZONE_DEVICE driver. > > > > Why pmem hasn't initialized struct pages? > > We proposed to initialize in previous approach but that wasn't merged. > (See https://marc.info/?l=linux-mm&m=152964792500739&w=2) > > > Isn't that a bug that should be addressed rather than paper over it like > > this? > > I'm not sure. What do you think, Dan?
Yeah, I am really curious about details. Why do we keep uninitialized struct pages at all? What is a random pfn walker supposed to do? What kind of metadata would be clobbered? In other words much more details please. -- Michal Hocko SUSE Labs
