Re: [syzbot] [x86?] BUG: soft lockup in xfrm_timer_handler

[Dave Hansen]

On 8/18/25 00:59, syzbot wrote:
> Call Trace:
>  <IRQ>
...
>  spin_lock include/linux/spinlock.h:351 [inline]
>  __xfrm_state_delete+0xba/0xca0 net/xfrm/xfrm_state.c:818
>  xfrm_timer_handler+0x18f/0xa00 net/xfrm/xfrm_state.c:716
>  __run_hrtimer kernel/time/hrtimer.c:1761 [inline]
>  __hrtimer_run_queues+0x52c/0xc60 kernel/time/hrtimer.c:1825
>  hrtimer_run_softirq+0x187/0x2b0 kernel/time/hrtimer.c:1842
>  handle_softirqs+0x283/0x870 kernel/softirq.c:579
>  __do_softirq kernel/softirq.c:613 [inline]
>  invoke_softirq kernel/softirq.c:453 [inline]
>  __irq_exit_rcu+0xca/0x1f0 kernel/softirq.c:680
>  irq_exit_rcu+0x9/0x30 kernel/softirq.c:696
>  instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline]
>  sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1050

>From that call trace, I'd suspect a deadlock from the xfrm code not
releasing the lock somewhere, not x86 code.

One thing that stands out is that of the ~20 or so uses of
'->xfrm.xfrm_state_lock', the call site in the trace is the only one
that uses spin_lock() instead of spin_lock_bh(). I didn't look at it for
long, so maybe there's a good reason for it. But it did catch my eye.