This is a note to let you know that I've just added the patch titled
init, sched: Fix race between init and kthreadd
to the 2.6.32-longterm tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/longterm/longterm-queue-2.6.32.git;a=summary
The filename of the patch is:
init-sched-fix-race-between-init-and-kthreadd.patch
and it can be found in the queue-2.6.32 subdirectory.
If you, or anyone else, feels it should not be added to the 2.6.32 longterm
tree,
please let <[email protected]> know about it.
>From 56d7647a85abc9b2a8b8e12d2edb08f91faee3db Mon Sep 17 00:00:00 2001
From: Peter Zijlstra <[email protected]>
Date: Mon, 28 Jun 2010 16:51:01 +0200
Subject: init, sched: Fix race between init and kthreadd
From: Peter Zijlstra <[email protected]>
commit b433c3d4549ae74935b585115f076c6fb7bc48fe upstream.
Ilya reported that on a very slow machine he could reliably
reproduce a race between forking init and kthreadd. We first
fork init so that it obtains pid-1, however since the scheduler
is already fully running at this point it can preempt and run
the init thread before we spawn and set kthreadd_task.
The init thread can then attempt spawning kthreads without
kthreadd being present which results in an OOPS.
Reported-by: Ilya Loginov <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Acked-by: Linus Torvalds <[email protected]>
LKML-Reference: <1277736661.3561.110.camel@laptop>
Signed-off-by: Ingo Molnar <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
init/main.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
--- a/init/main.c
+++ b/init/main.c
@@ -407,16 +407,24 @@ static void __init setup_command_line(ch
* gcc-3.4 accidentally inlines this function, so use noinline.
*/
+static __initdata DECLARE_COMPLETION(kthreadd_done);
+
static noinline void __init_refok rest_init(void)
__releases(kernel_lock)
{
int pid;
rcu_scheduler_starting();
+ /*
+ * We need to spawn init first so that it obtains pid-1, however
+ * the init task will end up wanting to create kthreads, which, if
+ * we schedule it before we create kthreadd, will OOPS.
+ */
kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
numa_default_policy();
pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
+ complete(&kthreadd_done);
unlock_kernel();
/*
@@ -841,6 +849,10 @@ static noinline int init_post(void)
static int __init kernel_init(void * unused)
{
+ /*
+ * Wait until kthreadd is all set-up.
+ */
+ wait_for_completion(&kthreadd_done);
lock_kernel();
/*
Patches currently in longterm-queue-2.6.32 which might be from
[email protected] are
/home/gregkh/linux/longterm/longterm-queue-2.6.32/queue-2.6.32/perf-tools-add-make-debug-1-to-remove-the-o6-cflag.patch
/home/gregkh/linux/longterm/longterm-queue-2.6.32/queue-2.6.32/init-sched-fix-race-between-init-and-kthreadd.patch
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