I can systematically reproduce the following soft lockup w/ the latest
5.15-rc4 kernel (and all the 5.14, 5.13 and 5.12 kernels that I've
tested so far).
I've found this issue by running systemd autopkgtest (I'm using the
latest systemd in Ubuntu - 248.3-1ubuntu7 - but it should happen with
any recent version of systemd).
I'm running this test inside a local KVM instance and apparently systemd
is starting up its own KVM instances to run its tests, so the context is
a nested KVM scenario (even if I don't think the nested KVM part really
matters).
Here's the oops:
[ 36.466565] watchdog: BUG: soft lockup - CPU#0 stuck for 26s! [udevadm:333]
[ 36.466565] Modules linked in: btrfs blake2b_generic zstd_compress raid10 raid456 async_raid6_recov async_memcpy async_pq async_xor async_tx xor raid6_pq libcrc32c raid1 raid0 multipath linear psmouse floppy
[ 36.466565] CPU: 0 PID: 333 Comm: udevadm Not tainted 5.15-rc4
[ 36.466565] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.14.0-2 04/01/2014
[ 36.466565] RIP: 0010:__kmalloc_node+0xcf/0x370
[ 36.466565] Code: 00 85 c0 74 20 49 8b 45 00 a8 03 0f 85 8e 02 00 00 65 48 ff 08 e8 01 7a e3 ff 45 31 ff e9 a3 00 00 00 45 31 ed 4d 85 f6 74 f0 <0f> 1f 44 00 00 48 c7 45 c8 00 00 00 00 4d 8b 06 65 4c 03 05 19 87
[ 36.466565] RSP: 0018:ffffb512802c3aa8 EFLAGS: 00000286
[ 36.466565] RAX: 0000000000000000 RBX: 0000000000000dc0 RCX: 0000000000000000
[ 36.466565] RDX: 0000000000000000 RSI: 0000000000000dc0 RDI: ffff998601042700
[ 36.466565] RBP: ffffb512802c3af0 R08: ffffeb90800b5c00 R09: 0000000000000000
[ 36.466565] R10: 0000000000000293 R11: ffff99861e02f448 R12: 0000000000000dc0
[ 36.466565] R13: 0000000000000000 R14: ffff998601042700 R15: ffffffff8b519c4d
[ 36.466565] FS: 00007f08d0674d00(0000) GS:ffff99861e000000(0000) knlGS:0000000000000000
[ 36.466565] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 36.466565] CR2: 00005622f86e3108 CR3: 00000000033c8000 CR4: 00000000000006f0
[ 36.466565] Call Trace:
[ 36.466565] memcg_alloc_page_obj_cgroups+0x3d/0x90
[ 36.466565] allocate_slab+0xc1/0x440
[ 36.466565] ? get_any_partial+0x85/0x190
[ 36.466565] new_slab+0x3a/0x60
[ 36.466565] ___slab_alloc+0x562/0x6b0
[ 36.466565] ? __alloc_file+0x28/0xe0
[ 36.466565] ? __alloc_file+0x28/0xe0
[ 36.466565] ? dput+0x84/0x180
[ 36.466565] ? step_into+0x312/0x380
[ 36.466565] kmem_cache_alloc+0x299/0x2d0
[ 36.466565] ? __alloc_file+0x28/0xe0
[ 36.466565] __alloc_file+0x28/0xe0
[ 36.466565] alloc_empty_file+0x45/0xc0
[ 36.466565] path_openat+0x47/0x2b0
[ 36.466565] do_filp_open+0xb2/0x150
[ 36.466565] ? putname+0x55/0x60
[ 36.466565] ? __check_object_size.part.0+0x128/0x150
[ 36.466565] ? __check_object_size+0x19/0x20
[ 36.466565] ? alloc_fd+0x53/0x170
[ 36.466565] do_sys_openat2+0x9b/0x160
[ 36.466565] __x64_sys_openat+0x55/0x90
[ 36.466565] do_syscall_64+0x5c/0xc0
[ 36.466565] ? exit_to_user_mode_prepare+0x37/0xb0
[ 36.466565] ? syscall_exit_to_user_mode+0x27/0x50
[ 36.466565] ? __x64_sys_newfstatat+0x1c/0x20
[ 36.466565] ? do_syscall_64+0x69/0xc0
[ 36.466565] ? do_syscall_64+0x69/0xc0
[ 36.466565] ? do_syscall_64+0x69/0xc0
[ 36.466565] entry_SYSCALL_64_after_hwframe+0x44/0xae
[ 36.466565] RIP: 0033:0x7f08d0c0466b
[ 36.466565] Code: 25 00 00 41 00 3d 00 00 41 00 74 4b 64 8b 04 25 18 00 00 00 85 c0 75 67 44 89 e2 48 89 ee bf 9c ff ff ff b8 01 01 00 00 0f 05 <48> 3d 00 f0 ff ff 0f 87 91 00 00 00 48 8b 4c 24 28 64 48 2b 0c 25
[ 36.466565] RSP: 002b:00007ffe10be08f0 EFLAGS: 00000246 ORIG_RAX: 0000000000000101
[ 36.466565] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f08d0c0466b
[ 36.466565] RDX: 0000000000080000 RSI: 00007ffe10be0a70 RDI: 00000000ffffff9c
[ 36.466565] RBP: 00007ffe10be0a70 R08: fefefefefefefeff R09: fefefeff716e6c71
[ 36.466565] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000080000
[ 36.466565] R13: 00005622f86e2520 R14: 0000000000000003 R15: 00007ffe10be0990
It looks like this is pointing at asm_volatile_goto():
crash> gdb list *(__kmalloc_node+0xcf)
0xffffffff8b4f8e3f is in __kmalloc_node (/build/impish/arch/x86/include/asm/jump_label.h:27).
22
23 #ifdef CONFIG_STACK_VALIDATION
24
25 static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
26 {
27 asm_volatile_goto("1:"
28 "jmp %l[l_yes] # objtool NOPs this \n\t"
29 JUMP_TABLE_ENTRY
30 : : "i" (key), "i" (2 | branch) : : l_yes);
31
And it seems that we're hitting an int3:
crash> bt 1
PID: 1 TASK: ffff998601248000 CPU: 3 COMMAND: "systemd"
[exception RIP: poke_int3_handler+89]
RIP: ffffffff8be6ac89 RSP: ffffb51280013b80 RFLAGS: 00000046
RAX: 000000008c0010a7 RBX: 0000000000000000 RCX: ffffb51280013ba8
RDX: 0000000000000000 RSI: ffffffff8c000a99 RDI: ffffb51280013ba8
RBP: ffffb51280013b98 R8: 0000000000000000 R9: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffb51280013ba8
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
CS: 0010 SS: 0018
#0 [ffffb51280013b80] exc_int3 at ffffffff8be69e80
#1 [ffffb51280013ba0] asm_exc_int3 at ffffffff8c000aa1
#2 [ffffb51280013c28] __kmalloc_node at ffffffff8b4f8e40
#3 [ffffb51280013c80] __kmalloc_node at ffffffff8b4f8e16
#4 [ffffb51280013cd8] kvmalloc_node at ffffffff8b4885c8
#5 [ffffb51280013d00] seq_read_iter at ffffffff8b56139c
#6 [ffffb51280013d60] seq_read at ffffffff8b561585
#7 [ffffb51280013de8] vfs_read at ffffffff8b531b0f
#8 [ffffb51280013e28] ksys_read at ffffffff8b5321d7
#9 [ffffb51280013e68] __x64_sys_read at ffffffff8b532269
#10 [ffffb51280013e78] do_syscall_64 at ffffffff8be6900c
#11 [ffffb51280013f50] entry_SYSCALL_64_after_hwframe at ffffffff8c00007c
RIP: 00007fc076f2e912 RSP: 00007ffde04ba888 RFLAGS: 00000246
RAX: ffffffffffffffda RBX: 000055e3b310bc30 RCX: 00007fc076f2e912
RDX: 0000000000000400 RSI: 000055e3b31415e0 RDI: 0000000000000029
RBP: 00007fc077031560 R8: 0000000000000029 R9: 0000000000000050
R10: 0000000000001000 R11: 0000000000000246 R12: 00007fc07679a6c0
R13: 0000000000000d68 R14: 00007fc077030960 R15: 0000000000000d68
ORIG_RAX: 0000000000000000 CS: 0033 SS: 002b
If I disable CONFIG_KFENCE the soft lockup doesn't happen and systemd
autotest completes just fine.
We've decided to disable KFENCE in the latest Ubuntu Impish kernel
(5.13) for now, because of this issue, but I'm still investigating
trying to better understand the problem.
Any hint / suggestion?
Thanks,
-Andrea
