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Commit f9c42831 authored by Michael Bohan's avatar Michael Bohan Committed by Se Wang (Patrick) Oh
Browse files

printk: Don't take console semaphore in atomic context 



The CPU HOTPLUG take_cpu_down path is invokved with preemption
disabled via stop_machine. This causes a "Scheduling while
atomic" BUG when there is contention for the console semaphore.
The solution is to defer the console flush until it's not in
scheduling violation.

Change-Id: I2d0d58576a4db308ee40850a18a6bb9784ca4e4b
Signed-off-by: default avatarMichael Bohan <mbohan@codeaurora.org>
[mattw@codeaurora.org: adjust for moved location of printk.c]
Signed-off-by: default avatarMatt Wagantall <mattw@codeaurora.org>
parent d9479b68

kernel/printk/printk.c

+17 −0
Original line number Diff line number Diff line
@@ -2065,6 +2065,14 @@ void resume_console(void) 
	console_unlock();

}



static void __cpuinit console_flush(struct work_struct *work)

{

	console_lock();

	console_unlock();

}



static __cpuinitdata DECLARE_WORK(console_cpu_notify_work, console_flush);



/**

 * console_cpu_notify - print deferred console messages after CPU hotplug

 * @self: notifier struct
@@ -2075,6 +2083,9 @@ void resume_console(void) 
 * will be spooled but will not show up on the console.  This function is

 * called when a new CPU comes online (or fails to come up), and ensures

 * that any such output gets printed.

 *

 * Special handling must be done for cases invoked from an atomic context,

 * as we can't be taking the console semaphore here.

 */

static int console_cpu_notify(struct notifier_block *self,

	unsigned long action, void *hcpu)
@@ -2092,6 +2103,12 @@ static int console_cpu_notify(struct notifier_block *self, 
		console_unlock();

#endif

		break;

	/* invoked with preemption disabled, so defer */

	case CPU_DYING:

		if (!console_trylock())

			schedule_work(&console_cpu_notify_work);

		else

			console_unlock();

	}

	return NOTIFY_OK;

}