linux-kernel - Re: [syzbot] [x86?] BUG: soft lockup in xfrm_timer

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Message-ID: <95833405-18aa-48ad-a5d6-4f659dfbf08a@intel.com>
Date: Tue, 19 Aug 2025 07:46:35 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: syzbot <syzbot+b6ae1c4eede4e0ea287f@...kaller.appspotmail.com>,
 ajay.kaher@...adcom.com, alexey.makhalov@...adcom.com,
 bcm-kernel-feedback-list@...adcom.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, hpa@...or.com, jgross@...e.com,
 linux-kernel@...r.kernel.org, mingo@...hat.com,
 syzkaller-bugs@...glegroups.com, tglx@...utronix.de,
 virtualization@...ts.linux.dev, x86@...nel.org,
 Steffen Klassert <steffen.klassert@...unet.com>,
 Herbert Xu <herbert@...dor.apana.org.au>,
 "David S. Miller" <davem@...emloft.net>
Subject: Re: [syzbot] [x86?] BUG: soft lockup in xfrm_timer_handler

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.