FYI, we noticed the below changes on git://kernel.ubuntu.com/sforshee/linux.git userns-mounts commit 1d5ab0e98cf0282077fc1ac2b261d5237b26073e ("loop: Add loop filesystem") +------------------------------------------+------------+------------+ | | 87cad79097 | 1d5ab0e98c | +------------------------------------------+------------+------------+ | boot_successes | 12 | 0 | | boot_failures | 0 | 12 | | BUG:unable_to_handle_kernel | 0 | 12 | | Oops | 0 | 12 | | RIP:loopfs_sb_from_inode | 0 | 12 | | Kernel_panic-not_syncing:Fatal_exception | 0 | 12 | | backtrace:loop_add | 0 | 12 | | backtrace:loop_init | 0 | 12 | | backtrace:kernel_init_freeable | 0 | 12 | +------------------------------------------+------------+------------+ [ 3.923208] Floppy drive(s): fd0 is 1.44M [ 3.935689] FDC 0 is a S82078B [ 3.973524] brd: module loaded [ 3.980099] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 [ 3.981035] IP: [] loopfs_sb_from_inode+0x23/0x29 [ 3.981035] PGD 0 [ 3.981035] Oops: 0000 [#1] SMP [ 3.981035] Modules linked in: [ 3.981035] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.3.0-rc1-00034-g1d5ab0e #413 [ 3.981035] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014 [ 3.981035] task: ffff8800130a0000 ti: ffff8800130a8000 task.ti: ffff8800130a8000 [ 3.981035] RIP: 0010:[] [] loopfs_sb_from_inode+0x23/0x29 [ 3.981035] RSP: 0018:ffff8800130abdc8 EFLAGS: 00010246 [ 3.981035] RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffff880013c0ce06 [ 3.981035] RDX: 0000000000000000 RSI: 0000000000700000 RDI: 0000000000000000 [ 3.981035] RBP: ffff8800130abdc8 R08: 00000000be164353 R09: 0000000000000006 [ 3.981035] R10: ffff8800130abc10 R11: 00000000001db1f8 R12: 0000000000000000 [ 3.981035] R13: ffff8800001cdce0 R14: ffff8800150f6618 R15: 0000000000700000 [ 3.981035] FS: 0000000000000000(0000) GS:ffff880013c00000(0000) knlGS:0000000000000000 [ 3.981035] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b [ 3.981035] CR2: 0000000000000008 CR3: 000000000220f000 CR4: 00000000000006f0 [ 3.981035] Stack: [ 3.981035] ffff8800130abe18 ffffffff816dea08 ffff8800150f6618 0000000000000000 [ 3.981035] 0000000000000000 ffff8800130abc10 0000000000000000 ffff8800001cdce0 [ 3.981035] ffff8800150f6618 ffff8800001cda68 ffff8800130abe60 ffffffff816dc9d2 [ 3.981035] Call Trace: [ 3.981035] [] loopfs_new_dev+0x22/0x1a0 [ 3.981035] [] loop_add+0x270/0x2e5 [ 3.981035] [] loop_init+0x10c/0x162 [ 3.981035] [] ? brd_init+0x128/0x128 [ 3.981035] [] do_one_initcall+0xe7/0x177 [ 3.981035] [] kernel_init_freeable+0x1c2/0x24a [ 3.981035] [] ? rest_init+0x140/0x140 [ 3.981035] [] kernel_init+0xe/0xd4 [ 3.981035] [] ret_from_fork+0x3f/0x70 [ 3.981035] [] ? rest_init+0x140/0x140 [ 3.981035] Code: 41 5f 5d 49 8d 62 f8 c3 0f 1f 44 00 00 55 48 85 ff 48 89 e5 74 0e 48 8b 47 28 48 81 78 60 70 6f 6f 6c 74 0b 48 8b 05 18 e3 f7 01 <48> 8b 40 08 5d c3 0f 1f 44 00 00 55 48 89 e5 41 57 41 89 f7 41 [ 3.981035] RIP [] loopfs_sb_from_inode+0x23/0x29 [ 3.981035] RSP [ 3.981035] CR2: 0000000000000008 [ 3.981035] ---[ end trace 58d15d1469c4ff12 ]--- [ 3.981035] Kernel panic - not syncing: Fatal exception Thanks, Ying Huang