The patch titled
PM: prevent frozen user mode helpers from failing the freezing of tasks
has been added to the -mm tree. Its filename is
pm-prevent-frozen-user-mode-helpers-from-failing-the-freezing-of-tasks-rev-2.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: PM: prevent frozen user mode helpers from failing the freezing of tasks
From: Rafael J. Wysocki <rjw@xxxxxxx>
At present, if a user mode helper is running while
usermodehelper_pm_callback() is executed, the helper may be frozen and the
completion in call_usermodehelper_exec() won't be completed until user
space processes are thawed. As a result, the freezing of kernel threads
may fail, which is not desirable.
Prevent this from happening by introducing a counter of running user mode
helpers and allowing usermodehelper_pm_callback() to succeed for action =
PM_HIBERNATION_PREPARE or action = PM_SUSPEND_PREPARE only if there are no
helpers running. [Namely, usermodehelper_pm_callback() waits for at most
RUNNING_HELPERS_TIMEOUT for the number of running helpers to become zero
and fails if that doesn't happen.]
Special thanks to Uli Luckas <u.luckas@xxxxxxx>, Pavel Machek
<pavel@xxxxxx> and Oleg Nesterov <oleg@xxxxxxxxxx> for reviewing the
previous versions of this patch and for very useful comments.
Signed-off-by: Rafael J. Wysocki <rjw@xxxxxxx>
Acked-by: Uli Luckas <u.luckas@xxxxxxx>
Acked-by: Nigel Cunningham <nigel@xxxxxxxxxxxxxxxxxx>
Acked-by: Pavel Machek <pavel@xxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/kmod.c | 78 +++++++++++++++++++++++++++++++++++++++++-------
1 files changed, 68 insertions(+), 10 deletions(-)
diff -puN kernel/kmod.c~pm-prevent-frozen-user-mode-helpers-from-failing-the-freezing-of-tasks-rev-2 kernel/kmod.c
--- a/kernel/kmod.c~pm-prevent-frozen-user-mode-helpers-from-failing-the-freezing-of-tasks-rev-2
+++ a/kernel/kmod.c
@@ -41,14 +41,6 @@ extern int max_threads;
static struct workqueue_struct *khelper_wq;
-/*
- * If set, both call_usermodehelper_keys() and call_usermodehelper_pipe() exit
- * immediately returning -EBUSY. Used for preventing user land processes from
- * being created after the user land has been frozen during a system-wide
- * hibernation or suspend operation.
- */
-static int usermodehelper_disabled;
-
#ifdef CONFIG_KMOD
/*
@@ -275,15 +267,55 @@ static void __call_usermodehelper(struct
}
}
+#ifdef CONFIG_PM
+/*
+ * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
+ * (used for preventing user land processes from being created after the user
+ * land has been frozen during a system-wide hibernation or suspend operation).
+ */
+static int usermodehelper_disabled;
+
+/* Number of helpers running */
+static atomic_t running_helpers = ATOMIC_INIT(0);
+
+/*
+ * Wait queue head used by usermodehelper_pm_callback() to wait for all running
+ * helpers to finish.
+ */
+static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
+
+/*
+ * Time to wait for running_helpers to become zero before the setting of
+ * usermodehelper_disabled in usermodehelper_pm_callback() fails
+ */
+#define RUNNING_HELPERS_TIMEOUT (5 * HZ)
+
static int usermodehelper_pm_callback(struct notifier_block *nfb,
unsigned long action,
void *ignored)
{
+ long retval;
+
switch (action) {
case PM_HIBERNATION_PREPARE:
case PM_SUSPEND_PREPARE:
usermodehelper_disabled = 1;
- return NOTIFY_OK;
+ smp_mb();
+ /*
+ * From now on call_usermodehelper_exec() won't start any new
+ * helpers, so it is sufficient if running_helpers turns out to
+ * be zero at one point (it may be increased later, but that
+ * doesn't matter).
+ */
+ retval = wait_event_timeout(running_helpers_waitq,
+ atomic_read(&running_helpers) == 0,
+ RUNNING_HELPERS_TIMEOUT);
+ if (retval) {
+ return NOTIFY_OK;
+ } else {
+ usermodehelper_disabled = 0;
+ return NOTIFY_BAD;
+ }
case PM_POST_HIBERNATION:
case PM_POST_SUSPEND:
usermodehelper_disabled = 0;
@@ -293,6 +325,30 @@ static int usermodehelper_pm_callback(st
return NOTIFY_DONE;
}
+static void helper_lock(void)
+{
+ atomic_inc(&running_helpers);
+ smp_mb__after_atomic_inc();
+}
+
+static void helper_unlock(void)
+{
+ if (atomic_dec_and_test(&running_helpers))
+ wake_up(&running_helpers_waitq);
+}
+
+static void register_pm_notifier_callback(void)
+{
+ pm_notifier(usermodehelper_pm_callback, 0);
+}
+#else /* CONFIG_PM */
+#define usermodehelper_disabled 0
+
+static inline void helper_lock(void) {}
+static inline void helper_unlock(void) {}
+static inline void register_pm_notifier_callback(void) {}
+#endif /* CONFIG_PM */
+
/**
* call_usermodehelper_setup - prepare to call a usermode helper
* @path - path to usermode executable
@@ -397,6 +453,7 @@ int call_usermodehelper_exec(struct subp
DECLARE_COMPLETION_ONSTACK(done);
int retval;
+ helper_lock();
if (sub_info->path[0] == '\0') {
retval = 0;
goto out;
@@ -418,6 +475,7 @@ int call_usermodehelper_exec(struct subp
out:
call_usermodehelper_freeinfo(sub_info);
+ helper_unlock();
return retval;
}
EXPORT_SYMBOL(call_usermodehelper_exec);
@@ -459,5 +517,5 @@ void __init usermodehelper_init(void)
{
khelper_wq = create_singlethread_workqueue("khelper");
BUG_ON(!khelper_wq);
- pm_notifier(usermodehelper_pm_callback, 0);
+ register_pm_notifier_callback();
}
_
Patches currently in -mm which might be from rjw@xxxxxxx are
x86_64-set-the-irq_chip-name-for-lapic.patch
x86_64-pm_trace-support.patch
i386-do-not-restore-reserved-memory-after-hibernation.patch
i386-do-not-restore-reserved-memory-after-hibernation-fix.patch
x86_64-irq-use-mask-unmask-and-proper-locking-in-fixup_irqs-v2.patch
x86_64-irq-use-mask-unmask-and-proper-locking-in-fixup_irqs-v2-fix.patch
freezer-make-kernel-threads-nonfreezable-by-default.patch
freezer-make-kernel-threads-nonfreezable-by-default-fix.patch
freezer-make-kernel-threads-nonfreezable-by-default-fix-fix.patch
freezer-make-kernel-threads-nonfreezable-by-default-fix-2.patch
freezer-run-show_state-when-freezing-times-out.patch
pm-do-not-require-dev-spew-to-get-pm_debug.patch
swsusp-remove-incorrect-code-from-userc.patch
swsusp-remove-code-duplication-between-diskc-and-userc.patch
swsusp-remove-code-duplication-between-diskc-and-userc-fix.patch
swsusp-introduce-restore-platform-operations.patch
swsusp-fix-hibernation-code-ordering.patch
hibernation-prepare-to-enter-the-low-power-state.patch
freezer-avoid-freezing-kernel-threads-prematurely.patch
freezer-use-__set_current_state-in-refrigerator.patch
freezer-return-int-from-freeze_processes.patch
freezer-remove-redundant-check-in-try_to_freeze_tasks.patch
pm-introduce-hibernation-and-suspend-notifiers.patch
pm-introduce-hibernation-and-suspend-notifiers-fix.patch
pm-introduce-hibernation-and-suspend-notifiers-tidy.patch
pm-introduce-hibernation-and-suspend-notifiers-fix-fix.patch
pm-disable-usermode-helper-before-hibernation-and-suspend.patch
pm-disable-usermode-helper-before-hibernation-and-suspend-fix.patch
pm-reduce-code-duplication-between-mainc-and-userc.patch
pm-prevent-frozen-user-mode-helpers-from-failing-the-freezing-of-tasks-rev-2.patch
shrink_slab-handle-bad-shrinkers.patch
beeping-patch-for-debugging-acpi-sleep.patch
-
To unsubscribe from this list: send the line "unsubscribe mm-commits" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
