Subject: Re: linux-next: build failure after merge of the userns tree

From: "Eric W. Biederman" <[email-masked]>
Date: Wed, 16 Mar 2022 08:54:15 -0500

Stephen Rothwell <[email-masked]> writes:

> Hi all,
>
> After merging the userns tree, today's linux-next build (powerpc
> ppc64_defconfig) failed like this:
>
> kernel/sched/fair.c: In function 'init_numa_balancing':
> kernel/sched/fair.c:2884:9: error: implicit declaration of function 'init_task_work'; did you mean 'init_irq_work'? [-Werror=implicit-function-declaration]
>  2884 |         init_task_work(&p->numa_work, task_numa_work);
>       |         ^~~~~~~~~~~~~~
>       |         init_irq_work
> kernel/sched/fair.c: In function 'task_tick_numa':
> kernel/sched/fair.c:2935:25: error: implicit declaration of function 'task_work_add' [-Werror=implicit-function-declaration]
>  2935 |                         task_work_add(curr, work, TWA_RESUME);
>       |                         ^~~~~~~~~~~~~
> kernel/sched/fair.c:2935:51: error: 'TWA_RESUME' undeclared (first use in this function)
>  2935 |                         task_work_add(curr, work, TWA_RESUME);
>       |                                                   ^~~~~~~~~~
>
> Maybe caused by commit
>
>   03248addadf1 ("resume_user_mode: Move to resume_user_mode.h")
> or
>   8ca07e17c9dd ("task_work: Remove unnecessary include from posix_timers.h")

Yes.  That has the potential to have hidden a bug like this.

> interacting with (maybe) commit
>
>   c4ad6fcb67c4 ("sched/headers: Reorganize, clean up and optimize kernel/sched/fair.c dependencies")
>
> from the tip tree.
>

It is commit 4ff8f2ca6ccd ("sched/headers: Reorganize, clean up and
optimize kernel/sched/sched.h dependencies") that ultimately removes the
include of task_work.h from "sched.h".

But yes ideally commit c4ad6fcb67c4 ("sched/headers: Reorganize, clean
up and optimize kernel/sched/fair.c dependencies") would have added an
include of task_work.h into kernel/sched/fair.c

Ingo any chance you can fix this in your tree?  kernel/sched/fair.c
needs to include <linux/task_work.h> regardless. So I don't think this
is a bad thing.

Eric

> I have applied this merge fix patch.
>
> From: Stephen Rothwell <[email-masked]>
> Date: Wed, 16 Mar 2022 16:41:42 +1100
> Subject: [PATCH] fixup for moving of linux/task_work.h
>
> Signed-off-by: Stephen Rothwell <[email-masked]>
> ---
>  kernel/sched/fair.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 89d21fda106c..7a6678fdffb0 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -31,6 +31,7 @@
>  #include <linux/lockdep_api.h>
>  #include <linux/softirq.h>
>  #include <linux/refcount_api.h>
> +#include <linux/task_work.h>
>  #include <linux/topology.h>
>  #include <linux/sched/clock.h>
>  #include <linux/sched/cond_resched.h>
> -- 
>
> 2.34.1