FYI, we noticed the following commit: https://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git for-testing commit 1ef38d2db643a00884e5296ad7b8118509c070a6 ("mntns: Add a limit on the number of mount namespaces.") in testcase: boot on test machine: 4 threads qemu-system-x86_64 -enable-kvm -cpu IvyBridge with 2G memory caused below changes: +------------------------------------------+------------+------------+ | | 703286608a | 1ef38d2db6 | +------------------------------------------+------------+------------+ | boot_successes | 8 | 4 | | boot_failures | 0 | 4 | | general_protection_fault:#[##]SMP | 0 | 4 | | RIP:dec_ucount | 0 | 4 | | Kernel_panic-not_syncing:Fatal_exception | 0 | 4 | | backtrace:nfs_fs_mount | 0 | 4 | | backtrace:SyS_mount | 0 | 4 | +------------------------------------------+------------+------------+ [ 40.882582] /lkp/lkp/src/bin/run-lkp [ 40.916380] RESULT_ROOT=/result/boot/1/vm-ivb41-2G/debian-x86_64-2015-02-07.cgz/x86_64-allyesdebian/gcc-6/1ef38d2db643a00884e5296ad7b8118509c070a6/0 [ 40.922250] job=/lkp/scheduled/vm-ivb41-2G-1/boot-1-debian-x86_64-2015-02-07.cgz-1ef38d2db643a00884e5296ad7b8118509c070a6-20160809-97512-123arxg-0.yaml [ 41.013896] general protection fault: 0000 [#1] SMP [ 41.014931] Modules linked in: [ 41.016069] CPU: 3 PID: 863 Comm: mount.nfs Not tainted 4.8.0-rc1-00012-g1ef38d2 #180 [ 41.017628] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Debian-1.8.2-1 04/01/2014 [ 41.019613] task: ffff88007a9e00c0 task.stack: ffff88007d4d8000 [ 41.020811] RIP: 0010:[] [] dec_ucount+0x30/0x81 [ 41.022476] RSP: 0018:ffff88007d4dbcc0 EFLAGS: 00010206 [ 41.023554] RAX: ffff88007a9e00c0 RBX: 5a5a5a5a5a5a5a5a RCX: 5a5a5a5a5a5a5a8e [ 41.024966] RDX: 000000000001f3a0 RSI: 0000000000000005 RDI: 5a5a5a5a5a5a5a5a [ 41.028615] RBP: ffff88007d4dbce0 R08: 00000011f84cb2a8 R09: 0000000000000001 [ 41.029819] R10: ffff88009bb4ca98 R11: 0000000000000000 R12: ffffffff839ee3fc [ 41.031755] R13: 5a5a5a5a5a5a5a5a R14: 0000000000000034 R15: ffff88007d6ce920 [ 41.033459] FS: 00007f6b3a7a3880(0000) GS:ffff88009cc00000(0000) knlGS:0000000000000000 [ 41.035743] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 41.037087] CR2: 00000000015b6000 CR3: 000000007b4ca000 CR4: 00000000001406e0 [ 41.038868] Stack: [ 41.039756] ffff88007c870f00 ffff88007c870f00 ffff88007c93ef40 ffff88007c93ef40 [ 41.042211] ffff88007d4dbcf8 ffffffff812425c4 0000000000000000 ffff88007d4dbd30 [ 41.044951] ffffffff81242618 ffff88007c8908e0 ffff88007b1772b8 0000000000000000 [ 41.047647] Call Trace: [ 41.048382] [] put_mnt_ns+0x35/0x40 [ 41.049564] [] mount_subtree+0x49/0x7e [ 41.050859] [] nfs_follow_remote_path+0xde/0x127 [ 41.052619] [] nfs4_try_mount+0x49/0x4e [ 41.054050] [] nfs_fs_mount+0x816/0x847 [ 41.055607] [] ? lockdep_init_map+0xc3/0x1c6 [ 41.057082] [] ? nfs_initialise_sb+0x8c/0x8c [ 41.058259] [] ? param_set_portnr+0x48/0x48 [ 41.059781] [] mount_fs+0x67/0x131 [ 41.061091] [] ? mount_fs+0x67/0x131 [ 41.062210] [] vfs_kern_mount+0x6b/0xdb [ 41.063827] [] do_mount+0x708/0x97d [ 41.065151] [] ? copy_mount_options+0xba/0x124 [ 41.066790] [] SyS_mount+0x77/0x9f [ 41.068076] [] entry_SYSCALL_64_fastpath+0x1f/0xbd [ 41.069684] [] ? trace_hardirqs_off_caller+0x3f/0xab [ 41.071204] Code: 55 89 f6 48 89 e5 41 56 4c 8d 34 b5 20 00 00 00 41 55 49 89 fd 41 54 49 c7 c4 fc e3 9e 83 53 48 89 fb 48 85 db 74 44 4a 8d 0c 33 <8b> 11 89 d6 ff ce 78 0e 89 d0 f0 0f b1 31 39 c2 74 21 89 c2 eb [ 41.090703] RIP [] dec_ucount+0x30/0x81 [ 41.092106] RSP [ 41.093105] ---[ end trace b9983de5f2860fb3 ]--- [ 41.094220] Kernel panic - not syncing: Fatal exception FYI, raw QEMU command line is: qemu-system-x86_64 -enable-kvm -cpu IvyBridge -kernel /pkg/linux/x86_64-allyesdebian/gcc-6/1ef38d2db643a00884e5296ad7b8118509c070a6/vmlinuz-4.8.0-rc1-00012-g1ef38d2 -append 'ip=::::vm-ivb41-2G-1::dhcp root=/dev/ram0 user=lkp job=/lkp/scheduled/vm-ivb41-2G-1/boot-1-debian-x86_64-2015-02-07.cgz-1ef38d2db643a00884e5296ad7b8118509c070a6-20160809-97512-123arxg-0.yaml ARCH=x86_64 kconfig=x86_64-allyesdebian branch=linux-devel/devel-catchup-201608090432 commit=1ef38d2db643a00884e5296ad7b8118509c070a6 BOOT_IMAGE=/pkg/linux/x86_64-allyesdebian/gcc-6/1ef38d2db643a00884e5296ad7b8118509c070a6/vmlinuz-4.8.0-rc1-00012-g1ef38d2 max_uptime=600 RESULT_ROOT=/result/boot/1/vm-ivb41-2G/debian-x86_64-2015-02-07.cgz/x86_64-allyesdebian/gcc-6/1ef38d2db643a00884e5296ad7b8118509c070a6/0 LKP_SERVER=inn debug apic=debug sysrq_always_enabled rcupdate.rcu_cpu_stall_timeout=100 panic=-1 softlockup_panic=1 nmi_watchdog=panic oops=panic load_ramdisk=2 prompt_ramdisk=0 systemd.log_level=err ignore_loglevel earlyprintk=ttyS0,115200 console=ttyS0,115200 console=tty0 vga=normal rw' -initrd /fs/sda5/initrd-vm-ivb41-2G-1 -m 2560 -smp 4 -device e1000,netdev=net0 -netdev user,id=net0 -boot order=nc -no-reboot -watchdog i6300esb -watchdog-action debug -rtc base=localtime -drive file=/fs/sda5/disk0-vm-ivb41-2G-1,media=disk,if=virtio -drive file=/fs/sda5/disk1-vm-ivb41-2G-1,media=disk,if=virtio -drive file=/fs/sda5/disk2-vm-ivb41-2G-1,media=disk,if=virtio -drive file=/fs/sda5/disk3-vm-ivb41-2G-1,media=disk,if=virtio -drive file=/fs/sda5/disk4-vm-ivb41-2G-1,media=disk,if=virtio -drive file=/fs/sda5/disk5-vm-ivb41-2G-1,media=disk,if=virtio -pidfile /dev/shm/kboot/pid-vm-ivb41-2G-1 -serial file:/dev/shm/kboot/serial-vm-ivb41-2G-1 -daemonize -display none -monitor null Thanks, Xiaolong