Re: [PATCH] multithreaded coredumps for elf exeecutables

[Pavel Machek <pavel@suse.cz>]

Hi!

> - Other threads are prevented from executing while core dump is in 
>   progress to improve the accuracy of the dumps. This is done without 
>   changing the state of the task. We set cpus_allowed in task struct 
>   to be 0 to stop a task from being scheduled and reset it to -1 for
>   resume execution. This has the advantage to not depending on user
>   space at all for correct functioning. IMO sending SIGSTOP to stop 
>   other threads does not work if the process is being run under a 
>   debugger. The only possible issue with using cpus_allowed is that 

In swsusp patch, I had exactly the same problem. I created refrigerator(),
and halfway send a signal.... 

> +/*
> + * Suspend execution of other threads belonging to the same multithreaded process 
> + * of current, ASAP.
> + *
> + * Sets the current->cpu_mask to the current cpu to avoid cpu migration durring the dump.
> + * This cpu will also be the only cpu the other threads will be allowed to run after 
> + * coredump is completed. This seems to be needed to fix some SMP races.  This still
> + * needs some more thought though this solution works.

What about

app has 5 threads. 1st dumps core, and starts setting cpus_allowed mask to
thread 2. Meanwhile 3nd thread resets the mask back.

								Pavel?

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