[C/R] threaded application

[C/R] threaded application

[Sukadev Bhattiprolu]

Probably premature :-) but tried to C/R a simple threaded application
(running as container-init).

First got an -EINVAL due to following check in may_checkpoint_task():

        /*
         * FIX: for now, disallow siblings of container init created
         * via CLONE_PARENT (unclear if they will remain possible)
         */
        if (ctx->root_init && t != ctx->root_task &&
            t->real_parent == ctx->root_task->real_parent)

Assuming we are unintentionally excluding CLONE_THREAD with the
above check, I added a check for tgid:

        if (ctx->root_init && t != ctx->root_task &&
            t->real_parent == ctx->root_task->real_parent &&
            t->tgid != ctx->root_task->tgid) {

This got past the -EINVAL but the test failed the ckpt_obj_contained() check.

	c/r: FILE users 2 != count 6 objref 9

The main-thread opened a single file (log file). The other threads don't
write to it (yet). The count '6' corresponds to the number of threads in
the application.

I suspect that C/R code is incrementing obj->users once per thread for
the log file even though the threads share the file_struct reference.
(pthread_create() sets CLONE_FILES so the file_struct is shared between
threads).

Will post my test programs to Serge's new git-tree next week.

Sukadev

Re: [C/R] threaded application

[Oren Laadan]

Suka,

Thanks for the report.

Sukadev Bhattiprolu wrote:
> Probably premature :-) but tried to C/R a simple threaded application
> (running as container-init).
> 
> First got an -EINVAL due to following check in may_checkpoint_task():
> 
>         /*
>          * FIX: for now, disallow siblings of container init created
>          * via CLONE_PARENT (unclear if they will remain possible)
>          */
>         if (ctx->root_init && t != ctx->root_task &&
>             t->real_parent == ctx->root_task->real_parent)
> 
> Assuming we are unintentionally excluding CLONE_THREAD with the
> above check, I added a check for tgid:
> 
>         if (ctx->root_init && t != ctx->root_task &&
>             t->real_parent == ctx->root_task->real_parent &&
>             t->tgid != ctx->root_task->tgid) {
> 
> This got past the -EINVAL but the test failed the ckpt_obj_contained() check.

Yes, I see no reason to prevent multi-threaded container init.
Will add this to the ckpt-v15-dev git tree.

> 
> 	c/r: FILE users 2 != count 6 objref 9
> 
> The main-thread opened a single file (log file). The other threads don't
> write to it (yet). The count '6' corresponds to the number of threads in
> the application.
> 
> I suspect that C/R code is incrementing obj->users once per thread for
> the log file even though the threads share the file_struct reference.
> (pthread_create() sets CLONE_FILES so the file_struct is shared between
> threads).
> 

Indeed, the current code doesn't yet handle files_struct as a
shared object, so anything with CLONE_FILES isn't done correctly.
That's on the todo-list...

Oren.

> Will post my test programs to Serge's new git-tree next week.
> 
> Sukadev
>