linux-kernel - [RFC][PATCH] PM: Print a warning if firmware is requested when tasks are frozen

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Message-Id: <201105030044.51661.rjw@sisk.pl>
Date:	Tue, 3 May 2011 00:44:51 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	"Greg Kroah-Hartman" <gregkh@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [RFC][PATCH] PM: Print a warning if firmware is requested when tasks are frozen

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

Some drivers erroneously use request_firmware() from their ->resume()
(or ->thaw(), or ->restore()) callbacks, which is not going to work
unless the firmware has been built in.  This causes system resume to
stall until the firmware-loading timeout expires, which makes users
think that the resume has failed and reboot their machines
unnecessarily.  For this reason, make _request_firmware() print a
warning when it has been called when tasks are frozen and it's
impossible to start any new usermode helpers.

Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
---
 drivers/base/firmware_class.c |    3 +++
 include/linux/kmod.h          |    1 +
 kernel/kmod.c                 |    8 ++++++++
 3 files changed, 12 insertions(+)

Index: linux-2.6/include/linux/kmod.h
===================================================================
--- linux-2.6.orig/include/linux/kmod.h
+++ linux-2.6/include/linux/kmod.h
@@ -113,5 +113,6 @@ extern void usermodehelper_init(void);
 
 extern int usermodehelper_disable(void);
 extern void usermodehelper_enable(void);
+extern bool usermodehelper_is_disabled(void);
 
 #endif /* __LINUX_KMOD_H__ */
Index: linux-2.6/kernel/kmod.c
===================================================================
--- linux-2.6.orig/kernel/kmod.c
+++ linux-2.6/kernel/kmod.c
@@ -301,6 +301,14 @@ void usermodehelper_enable(void)
 	usermodehelper_disabled = 0;
 }
 
+/**
+ * usermodehelper_is_disabled - check if new helpers are allowed to be started
+ */
+bool usermodehelper_is_disabled(void)
+{
+	return usermodehelper_disabled;
+}
+
 static void helper_lock(void)
 {
 	atomic_inc(&running_helpers);
Index: linux-2.6/drivers/base/firmware_class.c
===================================================================
--- linux-2.6.orig/drivers/base/firmware_class.c
+++ linux-2.6/drivers/base/firmware_class.c
@@ -521,6 +521,9 @@ static int _request_firmware(const struc
 	if (!firmware_p)
 		return -EINVAL;
 
+	if (WARN_ON(usermodehelper_is_disabled()))
+		return -EBUSY;
+
 	*firmware_p = firmware = kzalloc(sizeof(*firmware), GFP_KERNEL);
 	if (!firmware) {
 		dev_err(device, "%s: kmalloc(struct firmware) failed\n",
--
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