Re: [PATCH] firmware loader: don't cancel _nowait requests when helperis not yet available

[Stephen Boyd]

On 03/13/12 13:14, Rafael J. Wysocki wrote:
> All of those use cases are in fact of the "wait for user space to be thawed
> and then load the firmware" type, which I believe may be handled without
> changing that code.
>
> Why don't you make your kthread freezable, for one example?
>
> Why don't you use a freezable workqueue instead?
>

If we put it on the freezable workqueue or make it a freezable thread
will it work?

In my scenario a wakeup interrupt comes in that wakes us up from
suspend. Within that wakeup handler a work item is scheduled to the
freezable workqueue. That work item then calls request_firmware().

It looks like we call schedule() after thawing the workqueues and tasks
so the work item could run before usermodehelpers are enabled and then
request_firmware() would fail. Do we need something like this (ignore
the fact that we call usermodhelper_enable() twice)?

diff --git a/kernel/power/process.c b/kernel/power/process.c
index 7e42645..61bfa95 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -187,6 +187,7 @@ void thaw_processes(void)
        } while_each_thread(g, p);
        read_unlock(&tasklist_lock);
 
+       usermodehelper_enable();
        schedule();
        printk("done.\n");
 }


Is there a reason we disable usermodehelpers if
CONFIG_SUSPEND_FREEZER=n? Should we do this instead so that
usermodehelpers are only disabled if we freeze userspace? Also what is
that schedule() call in thaw_kernel_threads() for? It looks like we'll
call schedule between kernel thread thawing and userspace thawing. I
pushed out the schedule() call to the callers so that we don't call
schedule() until userspace is thawed.

diff --git a/kernel/power/process.c b/kernel/power/process.c
index 7e42645..8fae228 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -125,6 +125,7 @@ int freeze_processes(void)
 	if (!pm_freezing)
 		atomic_inc(&system_freezing_cnt);
 
+	usermodehelper_disable();
 	printk("Freezing user space processes ... ");
 	pm_freezing = true;
 	error = try_to_freeze_tasks(true);
@@ -187,6 +188,7 @@ void thaw_processes(void)
 	} while_each_thread(g, p);
 	read_unlock(&tasklist_lock);
 
+	usermodehelper_enable();
 	schedule();
 	printk("done.\n");
 }
@@ -207,6 +209,5 @@ void thaw_kernel_threads(void)
 	} while_each_thread(g, p);
 	read_unlock(&tasklist_lock);
 
-	schedule();
 	printk("done.\n");
 }
diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index 4fd51be..1ab3e59 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -101,17 +101,12 @@ static int suspend_prepare(void)
 	if (error)
 		goto Finish;
 
-	error = usermodehelper_disable();
-	if (error)
-		goto Finish;
-
 	error = suspend_freeze_processes();
 	if (!error)
 		return 0;
 
 	suspend_stats.failed_freeze++;
 	dpm_save_failed_step(SUSPEND_FREEZE);
-	usermodehelper_enable();
  Finish:
 	pm_notifier_call_chain(PM_POST_SUSPEND);
 	pm_restore_console();
@@ -259,7 +254,6 @@ int suspend_devices_and_enter(suspend_state_t state)
 static void suspend_finish(void)
 {
 	suspend_thaw_processes();
-	usermodehelper_enable();
 	pm_notifier_call_chain(PM_POST_SUSPEND);
 	pm_restore_console();
 }
diff --git a/kernel/power/user.c b/kernel/power/user.c
index 3e10007..1a8fd6f 100644
--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -222,14 +222,8 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 		sys_sync();
 		printk("done.\n");
 
-		error = usermodehelper_disable();
-		if (error)
-			break;
-
 		error = freeze_processes();
-		if (error)
-			usermodehelper_enable();
-		else
+		if (!error)
 			data->frozen = 1;
 		break;
 
@@ -238,7 +232,6 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 			break;
 		pm_restore_gfp_mask();
 		thaw_processes();
-		usermodehelper_enable();
 		data->frozen = 0;
 		break;
 
@@ -251,6 +244,7 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 		error = hibernation_snapshot(data->platform_support);
 		if (error) {
 			thaw_kernel_threads();
+			schedule();
 		} else {
 			error = put_user(in_suspend, (int __user *)arg);
 			if (!error && !freezer_test_done)
@@ -258,6 +252,7 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 			if (freezer_test_done) {
 				freezer_test_done = false;
 				thaw_kernel_threads();
+				schedule();
 			}
 		}
 		break;
@@ -285,6 +280,7 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 		 * might fail or even deadlock).
 		 */
 		thaw_kernel_threads();
+		schedule();
 		break;
 
 	case SNAPSHOT_PREF_IMAGE_SIZE:

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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