linux-kernel - Re: BUG: soft lockup in smp_call

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Date:   Wed, 13 Sep 2023 23:30:23 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Hillf Danton <hdanton@...a.com>,
        Sanan Hasanov <Sanan.Hasanov@....edu>,
        Thomas Gleixner <tglx@...utronix.de>, peterz@...radead.org
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        syzkaller@...glegroups.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: BUG: soft lockup in smp_call_function

On 2023/09/13 20:07, Hillf Danton wrote:
> 
> 	cpu1			cpu4 (see below)
> 	====			====
> 	drm_crtc_vblank_off	__run_hrtimer
> 	spin_lock_irq(&dev->event_lock);
> 	...
> 				drm_handle_vblank
> 	hrtimer_cancel		spin_lock_irqsave(&dev->event_lock, irqflags);
> 
> 
> Deadlock should have been reported instead provided the lockdep_map in
> struct timer_list were added also to hrtimer, so it is highly appreciated
> if Tetsuo or Thomas adds it before 6.8 or 6.10.

Not me. ;-)

Since hrtimer_cancel() retries forever until lock_hrtimer_base() succeeds,
we want to add a lockdep annotation into hrtimer_cancel() so that we can
detect this type of deadlock?