linux-kernel - Re: [PATCH] Fix scheduling-while-atomic problem in console_cpu

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Message-ID: <20121016043559.GA32179@linux.vnet.ibm.com>
Date:	Mon, 15 Oct 2012 21:35:59 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	cernekee@...il.com, torbenh@....de, torvalds@...ux-foundation.org,
	tglx@...utronix.de, srivatsa.bhat@...ux.vnet.ibm.com
Subject: Re: [PATCH] Fix scheduling-while-atomic problem in
 console_cpu_notify()

On Mon, Oct 15, 2012 at 05:31:28PM -0700, Paul E. McKenney wrote:
> The console_cpu_notify( function runs with interrupts disabled in
> the CPU_DEAD case.  It therefore cannot block, for example, as will
> happen when it calls console_lock().  Therefore, remove the CPU_DEAD
> leg of the switch statement to avoid this problem.
> 
> Signed-off-by: Paul E. McKenney <paul.mckenney@...aro.org>

s/CPU_DEAD/CPU_DYING/

Apparently it is a bad idea to compose and send a patch while in a
C++ standards committee meeting where people are arguing about async
futures...  Fixed patch below.

							Thanx, Paul

------------------------------------------------------------------------

printk: Fix scheduling-while-atomic problem in console_cpu_notify()

The console_cpu_notify( function runs with interrupts disabled in
the CPU_DYING case.  It therefore cannot block, for example, as will
happen when it calls console_lock().  Therefore, remove the CPU_DYING
leg of the switch statement to avoid this problem.

Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

diff --git a/kernel/printk.c b/kernel/printk.c
index 66a2ea3..2d607f4 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -1890,7 +1890,6 @@ static int __cpuinit console_cpu_notify(struct notifier_block *self,
 	switch (action) {
 	case CPU_ONLINE:
 	case CPU_DEAD:
-	case CPU_DYING:
 	case CPU_DOWN_FAILED:
 	case CPU_UP_CANCELED:
 		console_lock();

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