Re: [PATCH] ftrace: disable tracing for suspend to ram

From: Marcin Slusarz
Date: Wed Aug 27 2008 - 17:28:24 EST


On Wed, Aug 27, 2008 at 09:14:40AM -0400, Steven Rostedt wrote:
>
> I've been painstakingly debugging the issue with suspend to ram and
> ftraced. The 2.6.28 code does not have this issue, but since the mcount
> recording is not going to be in 27, this must be solved for the ftrace
> daemon version.
>
> The resume from suspend to ram would reboot because it was triple
> faulting. Debugging further, I found that calling the mcount function
> itself was not an issue, but it would fault when it incremented
> preempt_count. preempt_count is on the tasks info structure that is on the
> low memory address of the task's stack. For some reason, it could not
> write to it. Resuming out of suspend to ram does quite a lot of funny
> tricks to get to work, so it is not surprising at all that simply doing a
> preempt_disable() would cause a fault.
>
> Thanks to Rafael for suggesting to add a "while (1);" to find the place in
> resuming that is causing the fault. I would place the loop somewhere in
> the code, compile and reboot and see if it would either reboot (hit the
> fault) or simply hang (hit the loop). Doing this over and over again, I
> narrowed it down that it was happening in enable_nonboot_cpus.
>
> At this point, I found that it is easier to simply disable tracing around
> the suspend code, instead of searching for the particular function that
> can not handle doing a preempt_disable.
>
> This patch disables the tracer as it suspends and reenables it on resume.
>
> I tested this patch on my Laptop, and it can resume fine with the patch.
>
> Signed-off-by: Steven Rostedt <srostedt@xxxxxxxxxx>

You can add my:
Tested-by: Marcin Slusarz <marcin.slusarz@xxxxxxxxx>

Thanks!

Marcin
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