linux-kernel - Re: [regression] suspend stress test stalls within 30 minutes

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Date: Fri, 17 May 2024 11:48:44 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: Kalle Valo <kvalo@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>,
 Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 "Rafael J. Wysocki" <rafael@...nel.org>, x86@...nel.org,
 linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
 regressions@...ts.linux.dev, Jeff Johnson <quic_jjohnson@...cinc.com>
Subject: Re: [regression] suspend stress test stalls within 30 minutes

On 5/17/24 11:37, Kalle Valo wrote:
> While writing this email I found another way to continue the suspend
> after a stall: terminate rtcwake with CTRL-C in the ssh session running
> the for loop. That explains why 'sudo shutdown -h now' makes the suspend
> go forward, it most likely kills the stalled rtcwake process.

Could we try and figure out what rtcwake is doing during its stall?  A
couple of ideas:

You could strace it to see if it's hung in the kernel:

	strace -o strace.log rtcwake ... <args here>

You could look at its stack in /proc, like this:

# cat /proc/`pidof sleep`/stack
[<0>] hrtimer_nanosleep+0xb5/0x190
[<0>] common_nsleep+0x44/0x50
[<0>] __x64_sys_clock_nanosleep+0xcb/0x140
[<0>] do_syscall_64+0x65/0x140
[<0>] entry_SYSCALL_64_after_hwframe+0x6e/0x76

Or you can use sysrq:

	echo t > /proc/sysrq-trigger

to get *all* tasks' stacks dumped out to dmesg.

I'd probably do all three in that order.

Getting a function-graph trace of rtcwake during the stall would also be
nice, but that's a lot of data so let's try the easier things first.