Hi mm and ppc list, Recently I started to hit a kernel panic [2] rarely on *ppc64le* with *1k blocksize* ext4. It's not easy to reproduce, but still has chance to trigger by loop running generic/048 on ppc64le (not sure all kind of ppc64le can reproduce it). Although I've reported a bug to ext4 [1] (more details refer to [1]), but I only hit it on ppc64le until now, and I'm not sure if it's an ext4 related bug, more likes folio related issue, so I cc mm and ppc mail list, hope to get more reviewing. Thanks, Zorro [1] https://bugzilla.kernel.org/show_bug.cgi?id=216529 [2] [ 4638.919160] run fstests generic/048 at 2022-09-23 21:00:41 [ 4641.700564] EXT4-fs (sda3): mounted filesystem with ordered data mode. Quota mode: none. [ 4641.710999] EXT4-fs (sda3): shut down requested (1) [ 4641.718544] Aborting journal on device sda3-8. [ 4641.740342] EXT4-fs (sda3): unmounting filesystem. [ 4643.000415] EXT4-fs (sda3): mounted filesystem with ordered data mode. Quota mode: none. [ 4681.230907] BUG: Kernel NULL pointer dereference at 0x00000069 [ 4681.230922] Faulting instruction address: 0xc00000000068ee0c [ 4681.230929] Oops: Kernel access of bad area, sig: 11 [#1] [ 4681.230934] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries [ 4681.230942] Modules linked in: dm_flakey ext2 dm_snapshot dm_bufio dm_zero dm_mod loop ext4 mbcache jbd2 bonding rfkill tls sunrpc pseries_rng drm fuse drm_panel_orientation_quirks xfs libcrc32c sd_mod t10_pi sg ibmvscsi ibmveth scsi_transport_srp vmx_crypto [ 4681.230991] CPU: 0 PID: 82 Comm: kswapd0 Kdump: loaded Not tainted 6.0.0-rc6+ #1 [ 4681.230999] NIP: c00000000068ee0c LR: c00000000068f2b8 CTR: 0000000000000000 [ 4681.238525] REGS: c000000006c0b560 TRAP: 0380 Not tainted (6.0.0-rc6+) [ 4681.238532] MSR: 800000000280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 24028242 XER: 00000000 [ 4681.238556] CFAR: c00000000068edf4 IRQMASK: 0 [ 4681.238556] GPR00: c00000000068f2b8 c000000006c0b800 c000000002cf1700 c00c00000042f1c0 [ 4681.238556] GPR04: c000000006c0b860 0000000000000000 0000000000000002 0000000000000000 [ 4681.238556] GPR08: c000000002d404b0 0000000000000000 c00c00000042f1c0 0000000000000000 [ 4681.238556] GPR12: c0000000001cf080 c000000005100000 c000000000194298 c0000001fff9c480 [ 4681.238556] GPR16: c000000048cdb850 0000000000000007 0000000000000000 0000000000000000 [ 4681.238556] GPR20: 0000000000000001 c000000006c0b8f8 c00000000146b9d8 5deadbeef0000100 [ 4681.238556] GPR24: 5deadbeef0000122 c000000048cdb800 c000000006c0bc00 c000000006c0b8e8 [ 4681.238556] GPR28: c000000006c0b860 c00c00000042f1c0 0000000000000009 0000000000000009 [ 4681.238634] NIP [c00000000068ee0c] drop_buffers.constprop.0+0x4c/0x1c0 [ 4681.238643] LR [c00000000068f2b8] try_to_free_buffers+0x128/0x150 [ 4681.238650] Call Trace: [ 4681.238654] [c000000006c0b800] [c000000006c0b880] 0xc000000006c0b880 (unreliable) [ 4681.238663] [c000000006c0b840] [c000000006c0bc00] 0xc000000006c0bc00 [ 4681.238670] [c000000006c0b890] [c000000000498708] filemap_release_folio+0x88/0xb0 [ 4681.238679] [c000000006c0b8b0] [c0000000004c51c0] shrink_active_list+0x490/0x750 [ 4681.238688] [c000000006c0b9b0] [c0000000004c9f88] shrink_lruvec+0x3f8/0x430 [ 4681.238697] [c000000006c0baa0] [c0000000004ca1f4] shrink_node_memcgs+0x234/0x290 [ 4681.238704] [c000000006c0bb10] [c0000000004ca3c4] shrink_node+0x174/0x6b0 [ 4681.238711] [c000000006c0bbc0] [c0000000004cacf0] balance_pgdat+0x3f0/0x970 [ 4681.238718] [c000000006c0bd20] [c0000000004cb440] kswapd+0x1d0/0x450 [ 4681.238726] [c000000006c0bdc0] [c0000000001943d8] kthread+0x148/0x150 [ 4681.238735] [c000000006c0be10] [c00000000000cbe4] ret_from_kernel_thread+0x5c/0x64 [ 4681.238745] Instruction dump: [ 4681.238749] fbc1fff0 f821ffc1 7c7d1b78 7c9c2378 ebc30028 7fdff378 48000018 60000000 [ 4681.238765] 60000000 ebff0008 7c3ef840 41820048 <815f0060> e93f0000 5529077c 7d295378 [ 4681.238782] ---[ end trace 0000000000000000 ]--- [ 4681.270607] [ 4681.337460] Kernel attempted to read user page (6a) - exploit attempt? (uid: 0) [ 4681.337469] BUG: Kernel NULL pointer dereference on read at 0x0000006a [ 4681.337474] Faulting instruction address: 0xc00000000068ee0c [ 4681.337478] Oops: Kernel access of bad area, sig: 11 [#2] [ 4681.337481] LE PAGE_SIZE=64K MMU=Hash SMP NR_CPUS=2048 NUMA pSeries [ 4681.337486] Modules linked in: dm_flakey ext2 dm_snapshot dm_bufio dm_zero dm_mod loop ext4 mbcache jbd2 bonding rfkill tls sunrpc pseries_rng drm fuse drm_panel_orientation_quirks xfs libcrc32c sd_mod t10_pi sg ibmvscsi ibmveth scsi_transport_srp vmx_crypto [ 4681.337517] CPU: 2 PID: 704157 Comm: xfs_io Kdump: loaded Tainted: G D 6.0.0-rc6+ #1 [ 4681.337523] NIP: c00000000068ee0c LR: c00000000068f2b8 CTR: 0000000000000000 [ 4681.337527] REGS: c000000036006ef0 TRAP: 0300 Tainted: G D (6.0.0-rc6+) [ 4681.337532] MSR: 800000000280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 28428242 XER: 00000001 [ 4681.337546] CFAR: c00000000000c80c DAR: 000000000000006a DSISR: 40000000 IRQMASK: 0 [ 4681.337546] GPR00: c00000000068f2b8 c000000036007190 c000000002cf1700 c00c000000424740 [ 4681.337546] GPR04: c0000000360071f0 0000000000000000 0000000000000002 0000000000000000 [ 4681.337546] GPR08: c000000002d404b0 0000000000000000 c00c000000424740 0000000000000002 [ 4681.337546] GPR12: 0000000000000000 c00000000ffce400 0000000000000000 c0000001fff9c480 [ 4681.337546] GPR16: c00000004960e050 0000000000000007 0000000000000000 0000000000000000 [ 4681.337546] GPR20: 0000000000000001 c000000036007288 c00000000146b9d8 5deadbeef0000100 [ 4681.337546] GPR24: 5deadbeef0000122 c00000004960e000 c000000036007678 c000000036007278 [ 4681.337546] GPR28: c0000000360071f0 c00c000000424740 000000000000000a 000000000000000a [ 4681.337602] NIP [c00000000068ee0c] drop_buffers.constprop.0+0x4c/0x1c0 [ 4681.337608] LR [c00000000068f2b8] try_to_free_buffers+0x128/0x150 [ 4681.337613] Call Trace: [ 4681.337616] [c000000036007190] [c000000036007210] 0xc000000036007210 (unreliable) [ 4681.337622] [c0000000360071d0] [c000000036007678] 0xc000000036007678 [ 4681.337627] [c000000036007220] [c000000000498708] filemap_release_folio+0x88/0xb0 [ 4681.337633] [c000000036007240] [c0000000004c51c0] shrink_active_list+0x490/0x750 [ 4681.337640] [c000000036007340] [c0000000004c9f88] shrink_lruvec+0x3f8/0x430 [ 4681.337645] [c000000036007430] [c0000000004ca1f4] shrink_node_memcgs+0x234/0x290 [ 4681.337651] [c0000000360074a0] [c0000000004ca3c4] shrink_node+0x174/0x6b0 [ 4681.337656] [c000000036007550] [c0000000004cbd34] shrink_zones.constprop.0+0xd4/0x3e0 [ 4681.337661] [c0000000360075d0] [c0000000004cc158] do_try_to_free_pages+0x118/0x470 [ 4681.337667] [c000000036007650] [c0000000004cd084] try_to_free_pages+0x194/0x4c0 [ 4681.337673] [c000000036007720] [c00000000054cca4] __alloc_pages_slowpath.constprop.0+0x4f4/0xd80 [ 4681.337680] [c000000036007880] [c00000000054d95c] __alloc_pages+0x42c/0x580 [ 4681.337686] [c000000036007910] [c000000000587d88] alloc_pages+0xd8/0x1d0 [ 4681.337692] [c000000036007960] [c000000000587eb4] folio_alloc+0x34/0x90 [ 4681.337698] [c000000036007990] [c000000000498bc0] filemap_alloc_folio+0x40/0x60 [ 4681.337703] [c0000000360079b0] [c0000000004a0f54] __filemap_get_folio+0x224/0x790 [ 4681.337709] [c000000036007ab0] [c0000000004b4830] pagecache_get_page+0x30/0xb0 [ 4681.337715] [c000000036007ae0] [c008000003a9e4dc] ext4_da_write_begin+0x1a4/0x4f0 [ext4] [ 4681.337742] [c000000036007b70] [c000000000498e54] generic_perform_write+0xf4/0x2b0 [ 4681.337748] [c000000036007c20] [c008000003a7d190] ext4_buffered_write_iter+0xa8/0x1a0 [ext4] [ 4681.337770] [c000000036007c70] [c000000000615fc8] vfs_write+0x358/0x4b0 [ 4681.337776] [c000000036007d40] [c0000000006161f4] sys_pwrite64+0xd4/0x120 [ 4681.337782] [c000000036007da0] [c0000000000318d0] system_call_exception+0x180/0x430 [ 4681.337788] [c000000036007e10] [c00000000000be68] system_call_vectored_common+0xe8/0x278 [ 4681.337795] --- interrupt: 3000 at 0x7fff95651da4 [ 4681.337799] NIP: 00007fff95651da4 LR: 0000000000000000 CTR: 0000000000000000 [ 4681.337803] REGS: c000000036007e80 TRAP: 3000 Tainted: G D (6.0.0-rc6+) [ 4681.337807] MSR: 800000000280f033 <SF,VEC,VSX,EE,PR,FP,ME,IR,DR,RI,LE> CR: 48082402 XER: 00000000 [ 4681.337822] IRQMASK: 0 [ 4681.337822] GPR00: 00000000000000b4 00007ffffaa52530 00007fff95767200 0000000000000003 [ 4681.337822] GPR04: 0000010031ac0000 0000000000010000 0000000000490000 00007fff9581a5a0 [ 4681.337822] GPR08: 00007fff95812e68 0000000000000000 0000000000000000 0000000000000000 [ 4681.337822] GPR12: 0000000000000000 00007fff9581a5a0 0000000000a00000 ffffffffffffffff [ 4681.337822] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 4681.337822] GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000490000 [ 4681.337822] GPR24: 0000000000000049 0000000000000000 0000000000000000 0000000000010000 [ 4681.337822] GPR28: 0000010031ac0000 0000000000000003 0000000000000000 0000000000490000 [ 4681.337875] NIP [00007fff95651da4] 0x7fff95651da4 [ 4681.337878] LR [0000000000000000] 0x0 [ 4681.337881] --- interrupt: 3000 [ 4681.337884] Instruction dump: [ 4681.337887] fbc1fff0 f821ffc1 7c7d1b78 7c9c2378 ebc30028 7fdff378 48000018 60000000 [ 4681.337897] 60000000 ebff0008 7c3ef840 41820048 <815f0060> e93f0000 5529077c 7d295378 [ 4681.337908] ---[ end trace 0000000000000000 ]---
