From f47fc35555565c4b161c2e44b357b4dbaf3a997d Mon Sep 17 00:00:00 2001

From: Lennart Poettering <lennart@poettering.net>

Date: Sun, 12 Aug 2012 01:29:41 +0200

Subject: [PATCH] switch-root: remount to MS_PRIVATE

The kernel does not allow switching roots if things are mounted

MS_SHARED. As a work-around, remount things MS_PRIVATE before switching

roots.

This should be fixed in the kernel for good.

https://bugzilla.redhat.com/show_bug.cgi?id=847418

---

 src/core/shutdown.c    | 17 ++++++++---------

 src/core/switch-root.c |  9 +++++++++

 2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/src/core/shutdown.c b/src/core/shutdown.c

index 0b7cbd8..c3a4c39 100644

--- a/src/core/shutdown.c

+++ b/src/core/shutdown.c

@@ -104,15 +104,14 @@ static int pivot_to_new_root(void) {

                 return -errno;

         }

-        /*

-          In case some evil process made "/" MS_SHARED

-          It works for pivot_root, but the ref count for the root device

-          is not decreasing :-/

-        */

-        if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0) {

-                log_error("Failed to make \"/\" private mount %m");

-                return -errno;

-        }

+        /* Work-around for a kernel bug: for some reason the kernel

+         * refuses switching root if any file systems are mounted

+         * MS_SHARED. Hence remount them MS_PRIVATE here as a

+         * work-around.

+         *

+         * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */

+        if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)

+                log_warning("Failed to make \"/\" private mount: %m");

         if (pivot_root(".", "oldroot") < 0) {

                 log_error("pivot failed: %m");

diff --git a/src/core/switch-root.c b/src/core/switch-root.c

index 9832a52..efc7d34 100644

--- a/src/core/switch-root.c

+++ b/src/core/switch-root.c

@@ -56,6 +56,15 @@ int switch_root(const char *new_root) {

                 goto fail;

         }

+        /* Work-around for a kernel bug: for some reason the kernel

+         * refuses switching root if any file systems are mounted

+         * MS_SHARED. Hence remount them MS_PRIVATE here as a

+         * work-around.

+         *

+         * https://bugzilla.redhat.com/show_bug.cgi?id=847418 */

+        if (mount(NULL, "/", NULL, MS_REC|MS_PRIVATE, NULL) < 0)

+                log_warning("Failed to make \"/\" private mount: %m");

+

         NULSTR_FOREACH(i, move_mounts) {

                 char new_mount[PATH_MAX];

                 struct stat sb;

-- 

1.7.11.2