Messages in this thread | | | Date | Wed, 27 Aug 2008 23:27:25 +0200 | From | Marcin Slusarz <> | Subject | Re: [PATCH] ftrace: disable tracing for suspend to ram |
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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@redhat.com>
You can add my: Tested-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Thanks!
Marcin
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