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PM: prevent frozen user mode helpers from failing the freezing of tasks 

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@road.de>, Pavel Machek
<pavel@ucw.cz> and Oleg Nesterov <oleg@tv-sign.ru> for reviewing the
previous versions of this patch and for very useful comments.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Uli Luckas <u.luckas@road.de>
Acked-by: Nigel Cunningham <nigel@nigel.suspend2.net>
Acked-by: Pavel Machek <pavel@ucw.cz>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rafael J. Wysocki 2007-07-19 01:47:37 -07:00 committed by Linus Torvalds
parent 8cdd4936c1
commit ccd4b65aef
1 changed files with 68 additions and 10 deletions
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78
kernel/kmod.c
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@ -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 work_struct *work)
}
}
#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(struct notifier_block *nfb,
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 subprocess_info *sub_info,
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 subprocess_info *sub_info,
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();
}