Re: Early test: hangs in mm/compact.c w. Linus's 12d7aacab56e9ef185c

[Vlastimil Babka]

On 11/04/2014 10:36 AM, P. Christeas wrote:
> On Tuesday 04 November 2014, Vlastimil Babka wrote:
>> Please do keep testing (and see below what we need), and don't try
>> another tree - it's 3.18 we need to fix!
> Let me apologize/warn you about the poor quality of this report (and debug 
> data).
> It is on a system meant for everyday desktop usage, not kernel development. 
> Thus, it is tuned to be "slightly" debuggable ; mostly for performance.
> 
>> I'm not sure what you mean by "race" here and your snippet is
>> unfortunately just a small portion of the output ...
> 
> It is a shot in the dark. System becomes non-responsive (narrowed to desktop 
> apps waiting each other, or the X+kwin blocking), I can feel the CPU heating 
> and /sometimes/ disk I/O.
> 
> No BUG, Oops or any kernel message. (is printk level 4 adequate? )
> 
> Then, I try to drop to a console and collect as much data as possible with 
> SysRq.
> 
> The snippet I'd sent you is from all-cpus-backtrace (l), trying to see which 
> traces appear consistently during the lockup. There is also the huge traces of 
> "task-states" (t), but I reckon they are too noisy.
> That trace also matches the usage profile, because AFAICG[uess] the issue 
> appears when allocating during I/O load. 
> 
> After turning on full-preemption, I have been able to terminate/kill all tasks 
> and continue with same kernel but new userspace.
> 
>> OK so the process is not dead due to the problem? That probably rules
>> out some kinds of errors but we still need the full output. Thanks in
>> advance. 
>> I'm not aware of this, CCing lkml for wider coverage.
> 
> Thank you. As I've told in the first mail, this is an early report of possible 
> 3.18 regression. I'm trying to narrow down the case and make it reproducible 
> or get a good trace.

I see. I've tried to reproduce such issues with 3.18-rc3 but wasn't successful.
But I noticed a possible issue that could lead to your problem.
Can you please try the following patch?

--------8<-------