Run queue corruption issue

[greg@kroah.com (Greg KH)]

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.

And why are you using "raw_spin_lock()"?

> Kernel used: Linux 3.13

Wow that's obsolete and buggy, why use such an old thing?

greg k-h