linux-kernel - Re: [ BUG: Invalid wait context ] rtc_lock at: mc146818_avoid

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Message-ID: <20250403193659.hhUTgJLH@linutronix.de>
Date: Thu, 3 Apr 2025 21:36:59 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Borislav Petkov <bp@...en8.de>, linux-rtc@...r.kernel.org,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Mateusz Jończyk <mat.jonczyk@...pl>,
	lkml <linux-kernel@...r.kernel.org>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Frederic Weisbecker <frederic@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [ BUG: Invalid wait context ] rtc_lock at: mc146818_avoid_UIP

On 2025-04-03 15:50:32 [+0200], To Thomas Gleixner wrote:
> On 2025-04-03 15:12:08 [+0200], Thomas Gleixner wrote:
> > Converting it to a raw lock "fixes" the problem, but RT people will hunt
> > you down with a big latency bat.
> > 
> > But this is not related to the commit above and not new.
> > 
> > timekeeping_suspend() has always invoked mach_get_cmos_time() with the
> > freeze lock held and mc146818_get_time() has always locked rtc_lock.
> > 
> > I wonder, why this splat hasn't popped before. On RT lockdep should have
> > complained forever. Sebastian???
> 
> I sure haven't seen it. But it has to.

might_sleep() is quite because system_states is SYSTEM_SUSPEND.
lockdep seems to be quiet because I don't have an outer lock while
testing via
	echo mem > /sys/power/state

it is just
| WARNING: CPU: 0 PID: 1007 at kernel/time/timekeeping.c:1858 timekeeping_suspend+0x3b/0x330
| RIP: 0010:timekeeping_suspend+0x3b/0x330
| Call Trace:
|  <TASK>
|  syscore_suspend+0x80/0x2f0
|  suspend_devices_and_enter+0x21c/0xad0
|  pm_suspend+0x25c/0x6b0
|  state_store+0x68/0xd0
|  kernfs_fop_write_iter+0x15e/0x210
|  vfs_write+0x2bb/0x560
|  ksys_write+0x73/0xf0
|  do_syscall_64+0x91/0x1a0

> > Thanks,
> > 
> >         tglx

Sebastian