Mainline commit 8d610dd5 introduced the rootfs_initcall and moved
populate_rootfs out of start_kernel. This was because of issues
with userspace helpers being executed way too early. Things like
pipes weren't initialized yet and users were seeing Oopses or
unpredictable behavior in certain circumstances.
The fix worked by causing the execve to fail because it couldn't lookup
the helper in the file system since the file system wasn't populate yet.
It turns out that's a really late place to fail since the entire
usermodehelper infrastructure depends on a work queue that is already
checked to see if it has been initialized. We can fail earlier without
having to fork threads that will ultimately fail.
This patch moves populate_rootfs back to start_kernel and avoids the
race against a very early userspace by moving the initialization of
khelper_wq to rootfs_initcall.
This may seem like a small win, but it is essential for my next patch
which adds the ability to override ACPI tables at boot-time.
Signed-off-by: Jeff Mahoney <jeffm@xxxxxxxx>
---
include/linux/init.h | 1 +
init/initramfs.c | 3 +--
init/main.c | 10 +++++++++-
kernel/kmod.c | 1 +
4 files changed, 12 insertions(+), 3 deletions(-)
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -146,6 +146,7 @@ extern unsigned int reset_devices;
/* used by init/main.c */
void setup_arch(char **);
void prepare_namespace(void);
+int populate_rootfs(void);
extern void (*late_time_init)(void);
--- a/init/initramfs.c
+++ b/init/initramfs.c
@@ -565,7 +565,7 @@ static void __init clean_rootfs(void)
}
#endif
-static int __init populate_rootfs(void)
+int __init populate_rootfs(void)
{
char *err = unpack_to_rootfs(__initramfs_start,
__initramfs_end - __initramfs_start);
@@ -605,4 +605,3 @@ static int __init populate_rootfs(void)
}
return 0;
}
-rootfs_initcall(populate_rootfs);
--- a/init/main.c
+++ b/init/main.c
@@ -747,6 +747,15 @@ asmlinkage void __init start_kernel(void
check_bugs();
+ /*
+ * Do this before starting ACPI so we can read-in
+ * override tables before the tables are actually
+ * loaded. The usermode helper won't be initialized
+ * until much later so we don't race against things
+ * calling out to userspace.
+ */
+ populate_rootfs();
+
acpi_early_init(); /* before LAPIC and SMP init */
ftrace_init();
@@ -844,7 +853,6 @@ static void __init do_basic_setup(void)
rcu_init_sched(); /* needed by module_init stage. */
init_workqueues();
cpuset_init_smp();
- usermodehelper_init();
init_tmpfs();
driver_init();
init_irq_proc();
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -527,3 +527,4 @@ void __init usermodehelper_init(void)
khelper_wq = create_singlethread_workqueue("khelper");
BUG_ON(!khelper_wq);
}
+rootfs_initcall(usermodehelper_init);
--
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