Public bug reported:
== Summary ==
System hangs indefinitely during suspend-to-RAM. The kernel soft lockup
watchdog reports CPU stuck in smp_call_function_many_cond for thousands
of seconds, making the system unrecoverable without a hard reset.
== Environment ==
- Ubuntu 25.10 (Questing Quokka) / Kubuntu 25.10
- Kernel: 6.17.0-8-generic and 6.17.0-14-generic (both affected)
- Hardware: HP Z2 Tower G9 Workstation (Intel, PREEMPT(voluntary))
== Reproduction ==
1. Have a process using AF_PACKET raw socket (e.g. any network monitoring tool)
2. Suspend the system (systemctl suspend)
3. System hangs — never reaches actual suspend state, unrecoverable without
hard reset
== Call Trace ==
watchdog: BUG: soft lockup - CPU#21 stuck for 23s! [kworker/21:1:422]
Workqueue: events netstamp_clear
RIP: 0010:smp_call_function_many_cond+0x123/0x580
Call Trace:
<TASK>
? __pfx_do_sync_core+0x10/0x10
? tpacket_rcv+0x48e/0xde0
on_each_cpu_cond_mask+0x24/0x60
smp_text_poke_batch_finish+0x120/0x5b0
arch_jump_label_transform_apply+0x1a/0x30
__jump_label_update+0x100/0x120
jump_label_update+0xe1/0x110
static_key_enable_cpuslocked+0x86/0xb0
static_key_enable+0x1f/0x30
netstamp_clear+0x2d/0x50
process_one_work+0x18b/0x370
worker_thread+0x317/0x450
kthread+0x108/0x220
ret_from_fork+0x131/0x150
ret_from_fork_asm+0x1a/0x30
</TASK>
== Root Cause Analysis ==
When a process opens an AF_PACKET raw socket, the kernel schedules
netstamp_clear work via the workqueue. netstamp_clear calls
static_key_enable() which triggers jump_label modification via
smp_text_poke_batch_finish(). This requires all CPUs to synchronize
via smp_call_function_many_cond().
If suspend's freeze_processes() has already frozen other CPUs before
this IPI completes, the calling CPU waits forever for responses that
will never come, resulting in a permanent soft lockup.
The race condition:
CPU 21: netstamp_clear -> smp_text_poke_batch_finish -> waiting for all CPUs
Other CPUs: already frozen by freeze_processes() -> cannot respond to IPI
== Impact ==
System is completely unrecoverable from suspend without hard reset.
Affects any workload that uses AF_PACKET sockets (network monitoring,
packet capture tools, etc.). Confirmed on both 6.17.0-8 and 6.17.0-14.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/2143913
Title:
kernel: soft lockup in smp_call_function_many_cond during suspend -
netstamp_clear races with freeze_processes
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