Re: [PATCH v3 2/6] freezer,umh: Clean up freezer/initrd interaction

Will Deacon
2021-10-14T09:13:21Z

On Sat, Oct 09, 2021 at 12:07:56PM +0200, Peter Zijlstra wrote:
> handle_initrd() marks itself as PF_FREEZER_SKIP in order to ensure
> that the UMH, which is going to freeze the system, doesn't
> indefinitely wait for it's caller.
>
> Rework things by adding UMH_FREEZABLE to indicate the completion is
> freezable.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
> include/linux/umh.h | 9 +++++----
> init/do_mounts_initrd.c | 10 +---------
> kernel/umh.c | 8 ++++++++
> 3 files changed, 14 insertions(+), 13 deletions(-)

This looks much better to me:

Acked-by: Will Deacon <will@kernel.org>

Just a question on the old code:

> --- a/include/linux/umh.h
> +++ b/include/linux/umh.h
> @@ -11,10 +11,11 @@
> struct cred;
> struct file;
>
> -#define UMH_NO_WAIT 0 /* don't wait at all */
> -#define UMH_WAIT_EXEC 1 /* wait for the exec, but not the process */
> -#define UMH_WAIT_PROC 2 /* wait for the process to complete */
> -#define UMH_KILLABLE 4 /* wait for EXEC/PROC killable */
> +#define UMH_NO_WAIT 0x00 /* don't wait at all */
> +#define UMH_WAIT_EXEC 0x01 /* wait for the exec, but not the process */
> +#define UMH_WAIT_PROC 0x02 /* wait for the process to complete */
> +#define UMH_KILLABLE 0x04 /* wait for EXEC/PROC killable */
> +#define UMH_FREEZABLE 0x08 /* wait for EXEC/PROC freezable */
>
> struct subprocess_info {
> struct work_struct work;
> --- a/init/do_mounts_initrd.c
> +++ b/init/do_mounts_initrd.c
> @@ -79,19 +79,11 @@ static void __init handle_initrd(void)
> init_mkdir("/old", 0700);
> init_chdir("/old");
>
> - /*
> - * In case that a resume from disk is carried out by linuxrc or one of
> - * its children, we need to tell the freezer not to wait for us.
> - */
> - current->flags |= PF_FREEZER_SKIP;
> -
> info = call_usermodehelper_setup("/linuxrc", argv, envp_init,
> GFP_KERNEL, init_linuxrc, NULL, NULL);
> if (!info)
> return;
> - call_usermodehelper_exec(info, UMH_WAIT_PROC);
> -
> - current->flags &= ~PF_FREEZER_SKIP;

How was this supposed to work if it raced with the freezer checking the
flag?

Will