linux-kernel - [PATCH] fix problem with reschenduling in rest

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Message-Id: <20100624001148.61e9da1c.isloginov@gmail.com>
Date:	Thu, 24 Jun 2010 00:11:48 +0400
From:	Ilya Loginov <isloginov@...il.com>
To:	torvalds@...ux-foundation.org
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] fix problem with reschenduling in rest_init (2.6.35-rc3)

	There is a bug in rest_init function. The problem is that kernel_init
thread starts before initialization of kthreadd_task when
CONFIG_PREEMPT_VOLUNTARY is enabled.

kernel_init thread do wake_up_process(kthreadd_task) and I have kernel Oops in
try_to_wake_up when I try to get p->state.

	I found this problem on 2.6.34 on FPGA. It is very slow, and
find_task_by_pid is done after reschenduling. I have no this problem on
2.6.35-rc3 because kernel code is moved. But if I write simple loop like
	volatile int tmp;
	for(i = 0; i < preset_lpj; i++)
		tmp++;
right after kernel_thread(kernel_init,.... , I have this problem on
2.6.35-rc3 too.

	I understand that real problem is reschenduling in init code, but
I have no ability to fix it.

Signed-off-by: Ilya Loginov <isloginov@...il.com>
---
diff --git a/init/main.c b/init/main.c
index 3bdb152..9febd69 100644
--- a/init/main.c
+++ b/init/main.c
@@ -428,12 +428,12 @@ static noinline void __init_refok rest_init(void)
 	int pid;
 
 	rcu_scheduler_starting();
-	kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
 	numa_default_policy();
 	pid = kernel_thread(kthreadd, NULL, CLONE_FS | CLONE_FILES);
 	rcu_read_lock();
 	kthreadd_task = find_task_by_pid_ns(pid, &init_pid_ns);
 	rcu_read_unlock();
+	kernel_thread(kernel_init, NULL, CLONE_FS | CLONE_SIGHAND);
 	unlock_kernel();
 
 	/*
--
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