Re: Question regarding RT patches for ARM
Hi Sebastian, On 17 May 2017 at 18:02, Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
On 2017-05-17 07:45:39 [-0700], Eric Nelson wrote:
Hi Fawad, Hi Fawad,
On 05/17/2017 06:40 AM, Fawad Lateef wrote:
I'm not sure about the unhandled page fault, but the stalls may be because of the SDMA driver.
See this patch in the Freescale/NXP community for kernel 4.1: https://github.com/Freescale/meta-freescale/blob/master/recipes-kernel/linux...
That is something I see for the first time. The description says that it leads to this stall but it fails to explain _how_ it got there.
Thanks for the patch link. I will give it a try.
Talked to hardware manufacturer and they applied the patch.
Still that SDMA is only used for NOR flash and only u-boot and its environment are stored in nor flash. So not sure if that is going to help in any case.
SDMA is used for much more than NOR flash (SSI, USB, and sometimes UARTs).
So I would really like few more suggestions OR confirmations about ARM (cortex-A9 based imx6) (preemept)-RT support/patches are stable and can be used for final products.
I don't have any experience with the RT patches on 4.9 or later kernels, but do know that they're being used on i.MX6 with the vendor kernels (3.10.x, 4.1.x).
I just looked into a few boot logs and it seems the Phyflex board (imx6 quad) bootet v4.9.27-rt18, run cyclictest including some tests and nothing produced this "unhandled page fault" you mention here. This includes the previous RT version in the v4.9 line.
Thanks, seems like RT patches are quite stable for ARM then.
Of this "page fault" happens on boot, it has to do something without your .config + hw combination. If it happens at rune-time it is probably triggered by a driver or an application is triggering this.
Yes, this happens at run-time and not always. Sometimes hardware just hangs/stalls. As now RT is widely used on ARM so to me seems like it something related to hardware design/setting OR application. Another question: Is RT user-space application can make kernel/system crash? As to me kernel should kill the app but let itself running _but_ not sure in the case of RT patched kernel.
Regards,
Eric
Sebastian
Thanks, Fawad Lateef
On 2017-05-18 13:08:32 [+0200], Fawad Lateef wrote:
Hi Sebastian, Hi Fawad,
Of this "page fault" happens on boot, it has to do something without your .config + hw combination. If it happens at rune-time it is probably triggered by a driver or an application is triggering this.
Yes, this happens at run-time and not always. Sometimes hardware just hangs/stalls.
So this sounds like a race condition.
As now RT is widely used on ARM so to me seems like it something related to hardware design/setting OR application.
Another question: Is RT user-space application can make kernel/system crash? As to me kernel should kill the app but let itself running _but_ not sure in the case of RT patched kernel.
This is correct. With RT or without it: a use space should not be able to crash the kernel. It is possible that a race within a driver triggers more reliably on RT. I would recommend to strip down the system to the minimum where the issue should not trigger. And then slowly increase the "enabled" hardware components so you might get an idea when or what could cause it.
Thanks,
Fawad Lateef
Sebastian
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Sebastian Andrzej Siewior