Run queue corruption issue

[Jerrin Shaji George]

Hi Greg,

Thanks for your response.

On Tue, May 17, 2016 at 7:20 PM, Greg KH <greg at kroah.com> wrote:
> On Tue, May 17, 2016 at 06:55:07PM -0400, Jerrin Shaji George wrote:
>> Hi All,
>>
>> I wanted help with a piece of code that I have been working on.
>>
>> Please see -
>>
>> https://gist.github.com/jerrinsg/333e584d1f65dc95b9f13b61dcebdaa7
>>
>> I have written two function, migrate_to and migrate_back. migrate_to is used
>> to remove a process from the run queue, and migrate_back is used to insert this
>> process back into the run queue.
>>
>> The gist is from a taken from a larger project, where we are working on building
>> a mechanism to support thread migration across heterogeneous processors.
>> migrate_to_call() will be called by a thread which wants to remove itself from
>> the run queue (hence, it will pass the current task struct as the migration
>> argument). Once the other processor completes execution of the assigned task, it
>> will interrupt the main processor, which runs an interrupt handler, which in
>> turn calls the migrate_back_call() function. It passes the task struct of the
>> process that was removed from the run queue earlier to this function.
>>
>> This mechanism works fine the first few times, but when this process is repeated
>> many times in a loop, I am seeing a run queue corruption:
>> https://gist.github.com/jerrinsg/0ab09cd435d8d2cb6ae692c7e6f4f26b
>>
>> Is there anything wrong in the process dequeue or enqueue function that I have
>> written? Please help!
>
> volatile doesn't mean what you think it does, please don't use it in the
> kernel.
>

This flag was to be used for synchronization. I will change this.

> And why are you using "raw_spin_lock()"?

I used this seeing other usage in sched/core.c. Can please you let me know if I
should instead use a different function to lock the run queue?

>> Kernel used: Linux 3.13
>
> Wow that's obsolete and buggy, why use such an old thing?

This is the codebase that I inherited. Once I get the basic prototype working, I
will be working to port it to a newer version of the kernel.

>
> greg k-h