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

[Dave Hansen]

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.