linux-kernel - [RFC][PATCH 3/3] Freezer: Prevent ___call_usermodehelper from missing freezing requests

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Message-Id: <200702261152.18379.rjw@sisk.pl>
Date:	Mon, 26 Feb 2007 11:52:17 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Andrew Morton <akpm@...l.org>, Oleg Nesterov <oleg@...sign.ru>,
	Pavel Machek <pavel@....cz>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Aneesh Kumar <aneesh.kumar@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>
Subject: [RFC][PATCH 3/3] Freezer: Prevent ___call_usermodehelper from missing freezing requests

NOTE: Alternatively, we can just drop flush_signals() from there, but I'm not
sure that's the right thing to do.

---
From: Rafael J. Wysocki <rjw@...k.pl>

Since ____call_usermodehelper() calls flush_signals(current), the task that
enters it may miss a freezing request.  However, if ____call_usermodehelper()
clears TIF_FREEZE for the current task after flush_signals(current) returns, the
freezer will generate one more freezing request for this task.

Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
---
 kernel/kmod.c |    2 ++
 1 file changed, 2 insertions(+)

Index: linux-2.6.20-mm2/kernel/kmod.c
===================================================================
--- linux-2.6.20-mm2.orig/kernel/kmod.c	2007-02-25 12:07:15.000000000 +0100
+++ linux-2.6.20-mm2/kernel/kmod.c	2007-02-25 12:49:16.000000000 +0100
@@ -34,6 +34,7 @@
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/resource.h>
+#include <linux/freezer.h>
 #include <asm/uaccess.h>
 
 extern int delete_module(const char *name, unsigned int flags);
@@ -258,6 +259,7 @@ static int ____call_usermodehelper(void 
 	new_session = key_get(sub_info->ring);
 	flush_signals(current);
 	spin_lock_irq(&current->sighand->siglock);
+	do_not_freeze(current);
 	old_session = __install_session_keyring(current, new_session);
 	flush_signal_handlers(current, 1);
 	sigemptyset(&current->blocked);
-
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