Hi,
[BACKGROUND]
Recently I'm testing btrfs with 16KiB block size.
Currently btrfs is artificially limiting subpage block size to 4K.
But there is a simple patch to change it to support all block sizes <=
page size in my branch:
https://github.com/adam900710/linux/tree/larger_bs_support
[IOMAP WARNING]
And I'm running into a very weird kernel warning at btrfs/136, with 16K
block size and 64K page size.
The problem is, the problem happens with ext3 (using ext4 modeule) with
16K block size, and no btrfs is involved yet.
The test case btrfs/136 create an ext3 fs first, using the same block
size of the btrfs on TEST_DEV (so it's 16K).
Then populate the fs.
The hang happens at the ext3 populating part, with the following kernel
warning:
[ 989.664270] run fstests btrfs/136 at 2025-08-08 16:57:37
[ 990.551395] EXT4-fs (dm-3): mounting ext3 file system using the ext4
subsystem
[ 990.554980] EXT4-fs (dm-3): mounted filesystem
d90f4325-e6a6-4787-9da8-150ece277a94 r/w with ordered data mode. Quota
mode: none.
[ 990.581540] ------------[ cut here ]------------
[ 990.581551] WARNING: CPU: 3 PID: 434101 at fs/iomap/iter.c:34
iomap_iter_done+0x148/0x190
[ 990.583497] Modules linked in: dm_flakey nls_ascii nls_cp437 vfat fat
btrfs polyval_ce ghash_ce rtc_efi processor xor xor_neon raid6_pq
zstd_compress fuse loop nfnetlink qemu_fw_cfg ext4 crc16 mbcache jbd2
dm_mod xhci_pci xhci_hcd virtio_net virtio_scsi net_failover failover
virtio_console virtio_balloon virtio_blk virtio_mmio
[ 990.587247] CPU: 3 UID: 0 PID: 434101 Comm: fsstress Not tainted
6.16.0-rc7-custom+ #128 PREEMPT(voluntary)
[ 990.588525] Hardware name: QEMU KVM Virtual Machine, BIOS unknown
2/2/2022
[ 990.589414] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS
BTYPE=--)
[ 990.590314] pc : iomap_iter_done+0x148/0x190
[ 990.590874] lr : iomap_iter+0x174/0x230
[ 990.591370] sp : ffff8000880af740
[ 990.591800] x29: ffff8000880af740 x28: ffff0000db8e6840 x27:
0000000000000000
[ 990.592716] x26: 0000000000000000 x25: ffff8000880af830 x24:
0000004000000000
[ 990.593631] x23: 0000000000000002 x22: 000001bfdbfa8000 x21:
ffffa6a41c002e48
[ 990.594549] x20: 0000000000000001 x19: ffff8000880af808 x18:
0000000000000000
[ 990.595464] x17: 0000000000000000 x16: ffffa6a495ee6cd0 x15:
0000000000000000
[ 990.596379] x14: 00000000000003d4 x13: 00000000fa83b2da x12:
0000b236fc95f18c
[ 990.597295] x11: ffffa6a4978b9c08 x10: 0000000000001da0 x9 :
ffffa6a41c1a2a44
[ 990.598210] x8 : ffff8000880af5c8 x7 : 0000000001000000 x6 :
0000000000000000
[ 990.599125] x5 : 0000000000000004 x4 : 000001bfdbfa8000 x3 :
0000000000000000
[ 990.600040] x2 : 0000000000000000 x1 : 0000004004030000 x0 :
0000000000000000
[ 990.600955] Call trace:
[ 990.601273] iomap_iter_done+0x148/0x190 (P)
[ 990.601829] iomap_iter+0x174/0x230
[ 990.602280] iomap_fiemap+0x154/0x1d8
[ 990.602751] ext4_fiemap+0x110/0x140 [ext4]
[ 990.603350] do_vfs_ioctl+0x4b8/0xbc0
[ 990.603831] __arm64_sys_ioctl+0x8c/0x120
[ 990.604346] invoke_syscall+0x6c/0x100
[ 990.604836] el0_svc_common.constprop.0+0x48/0xf0
[ 990.605444] do_el0_svc+0x24/0x38
[ 990.605875] el0_svc+0x38/0x120
[ 990.606283] el0t_64_sync_handler+0x10c/0x138
[ 990.606846] el0t_64_sync+0x198/0x1a0
[ 990.607319] ---[ end trace 0000000000000000 ]---
[ 990.608042] ------------[ cut here ]------------
[ 990.608047] WARNING: CPU: 3 PID: 434101 at fs/iomap/iter.c:35
iomap_iter_done+0x164/0x190
[ 990.610842] Modules linked in: dm_flakey nls_ascii nls_cp437 vfat fat
btrfs polyval_ce ghash_ce rtc_efi processor xor xor_neon raid6_pq
zstd_compress fuse loop nfnetlink qemu_fw_cfg ext4 crc16 mbcache jbd2
dm_mod xhci_pci xhci_hcd virtio_net virtio_scsi net_failover failover
virtio_console virtio_balloon virtio_blk virtio_mmio
[ 990.619189] CPU: 3 UID: 0 PID: 434101 Comm: fsstress Tainted: G
W 6.16.0-rc7-custom+ #128 PREEMPT(voluntary)
[ 990.620876] Tainted: [W]=WARN
[ 990.621458] Hardware name: QEMU KVM Virtual Machine, BIOS unknown
2/2/2022
[ 990.622507] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS
BTYPE=--)
[ 990.623911] pc : iomap_iter_done+0x164/0x190
[ 990.624936] lr : iomap_iter+0x174/0x230
[ 990.626747] sp : ffff8000880af740
[ 990.627404] x29: ffff8000880af740 x28: ffff0000db8e6840 x27:
0000000000000000
[ 990.628947] x26: 0000000000000000 x25: ffff8000880af830 x24:
0000004000000000
[ 990.631024] x23: 0000000000000002 x22: 000001bfdbfa8000 x21:
ffffa6a41c002e48
[ 990.632278] x20: 0000000000000001 x19: ffff8000880af808 x18:
0000000000000000
[ 990.634189] x17: 0000000000000000 x16: ffffa6a495ee6cd0 x15:
0000000000000000
[ 990.635608] x14: 00000000000003d4 x13: 00000000fa83b2da x12:
0000b236fc95f18c
[ 990.637854] x11: ffffa6a4978b9c08 x10: 0000000000001da0 x9 :
ffffa6a41c1a2a44
[ 990.639181] x8 : ffff8000880af5c8 x7 : 0000000001000000 x6 :
0000000000000000
[ 990.642370] x5 : 0000000000000004 x4 : 000001bfdbfa8000 x3 :
0000000000000000
[ 990.644505] x2 : 0000004004030000 x1 : 0000004004030000 x0 :
0000004004030000
[ 990.645493] Call trace:
[ 990.645841] iomap_iter_done+0x164/0x190 (P)
[ 990.646377] iomap_iter+0x174/0x230
[ 990.647550] iomap_fiemap+0x154/0x1d8
[ 990.648052] ext4_fiemap+0x110/0x140 [ext4]
[ 990.649061] do_vfs_ioctl+0x4b8/0xbc0
[ 990.649704] __arm64_sys_ioctl+0x8c/0x120
[ 990.652141] invoke_syscall+0x6c/0x100
[ 990.653001] el0_svc_common.constprop.0+0x48/0xf0
[ 990.653909] do_el0_svc+0x24/0x38
[ 990.654332] el0_svc+0x38/0x120
[ 990.654736] el0t_64_sync_handler+0x10c/0x138
[ 990.655295] el0t_64_sync+0x198/0x1a0
[ 990.655761] ---[ end trace 0000000000000000 ]---
Considering it's not yet btrfs, and the call trace is from iomap, I
guess there is something wrong with ext4's ext3 support?
The involved ext4 kernel configs are the following:
# CONFIG_EXT2_FS is not set
# CONFIG_EXT3_FS is not set
CONFIG_EXT4_FS=m
CONFIG_EXT4_USE_FOR_EXT2=y
CONFIG_EXT4_FS_POSIX_ACL=y
CONFIG_EXT4_FS_SECURITY=y
# CONFIG_EXT4_DEBUG is not set
CONFIG_JBD2=m
# CONFIG_JBD2_DEBUG is not set
Thanks,
Qu
