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From: Kalle Valo <kvalo@kernel.org>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Borislav Petkov <bp@alien8.de>,  Pawan Gupta
 <pawan.kumar.gupta@linux.intel.com>,  Thomas Gleixner
 <tglx@linutronix.de>,  Ingo Molnar <mingo@redhat.com>,  Dave Hansen
 <dave.hansen@linux.intel.com>,  "Rafael J. Wysocki" <rafael@kernel.org>,
  x86@kernel.org,  linux-pm@vger.kernel.org,  linux-kernel@vger.kernel.org,
  regressions@lists.linux.dev,  Jeff Johnson <quic_jjohnson@quicinc.com>
Subject: Re: [regression] suspend stress test stalls within 30 minutes
References: <87o79cjjik.fsf@kernel.org>
	<20240511184847.GCZj-9j2sh1Akpt9iS@fat_crate.local>
	<20240511184945.GDZj-9yaOEWqf1ng8u@fat_crate.local>
	<87h6f4jdrq.fsf@kernel.org> <878r0djxgc.fsf@kernel.org>
	<874jb0jzx5.fsf@kernel.org>
	<20240514160555.GCZkOL41oB3hBt45eO@fat_crate.local>
	<87msoofjg1.fsf@kernel.org>
	<35086bb6-ee11-4ac6-b8ba-5fab20065b54@intel.com>
	<871q60ffnr.fsf@kernel.org>
	<7813dff5-b140-48c4-bc15-ed25c7a07591@intel.com>
Date: Fri, 17 May 2024 21:58:59 +0300
In-Reply-To: <7813dff5-b140-48c4-bc15-ed25c7a07591@intel.com> (Dave Hansen's
	message of "Fri, 17 May 2024 11:48:44 -0700")
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Dave Hansen <dave.hansen@intel.com> writes:

> 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.

I can do all that but most probably not this week. Luckily it's quite
easy to reproduce the bug, one time I even saw it in the first iteration
and usually within 15 minutes or so.

And do let me know if there's anything else I should try.

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