linux-kernel - [PATCH] apm-emulation: use wait_event_freezable() instead of freezer_[do_not

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Date:	Thu, 18 Aug 2011 10:06:53 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Jiri Kosina <jkosina@...e.cz>, linux-kernel@...r.kernel.org
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Russell King <linux@....linux.org.uk>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Paul Mundt <lethal@...ux-sh.org>
Subject: [PATCH] apm-emulation: use wait_event_freezable() instead of
 freezer_[do_not_]count()

vfork is moving away from freezer_[do_not_]count() one way or the
other leaving apm_ioctl() as the only user.  apm_ioctl() just wants to
wait for suspend/resume cycle to complete without hindering the
freezer.  Use wait_event_freezable() instead.

The only annoyance is that wait_event_freezable() wakes up with
-ERESTART if there are pending signals while apm_ioctl() wants to
ignore all signals until suspend is complete.  We can play with
@current->[real_]blocked but this is hardly a performance or latency
critical path - simply chill a bit on each iteration until
SUSPEND_DONE for unlikely cases where there are pending signals.

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: Oleg Nesterov <oleg@...hat.com>
---
Compile tested only.  It would be great if someone w/ affected
configuraiton can test this.

Thank you.

 drivers/char/apm-emulation.c |   16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

Index: work/drivers/char/apm-emulation.c
===================================================================
--- work.orig/drivers/char/apm-emulation.c
+++ work/drivers/char/apm-emulation.c
@@ -300,17 +300,13 @@ apm_ioctl(struct file *filp, u_int cmd, 
 			/*
 			 * Wait for the suspend/resume to complete.  If there
 			 * are pending acknowledges, we wait here for them.
+			 * wait_event_freezable() is interruptible and pending
+			 * signal can cause busy looping.  We aren't doing
+			 * anything critical, chill a bit on each iteration.
 			 */
-			freezer_do_not_count();
-
-			wait_event(apm_suspend_waitqueue,
-				   as->suspend_state == SUSPEND_DONE);
-
-			/*
-			 * Since we are waiting until the suspend is done, the
-			 * try_to_freeze() in freezer_count() will not trigger
-			 */
-			freezer_count();
+			while (wait_event_freezable(apm_suspend_waitqueue,
+					as->suspend_state == SUSPEND_DONE))
+				msleep(10);
 			break;
 		case SUSPEND_ACKTO:
 			as->suspend_result = -ETIMEDOUT;
--
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