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

Peter Zijlstra
2021-10-09T10:19:31Z

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(-)

--- 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;
+ call_usermodehelper_exec(info, UMH_WAIT_PROC|UMH_FREEZABLE);

/* move initrd to rootfs' /old */
init_mount("..", ".", NULL, MS_MOVE, NULL);
--- a/kernel/umh.c
+++ b/kernel/umh.c
@@ -28,6 +28,7 @@
#include <linux/async.h>
#include <linux/uaccess.h>
#include <linux/initrd.h>
+#include <linux/freezer.h>

#include <trace/events/module.h>

@@ -436,6 +437,9 @@ int call_usermodehelper_exec(struct subp
if (wait == UMH_NO_WAIT) /* task has freed sub_info */
goto unlock;

+ if (wait & UMH_FREEZABLE)
+ freezer_do_not_count();
+
if (wait & UMH_KILLABLE) {
retval = wait_for_completion_killable(&done);
if (!retval)
@@ -448,6 +452,10 @@ int call_usermodehelper_exec(struct subp
}

wait_for_completion(&done);
+
+ if (wait & UMH_FREEZABLE)
+ freezer_count();
+
wait_done:
retval = sub_info->retval;