Messages in this thread Patch in this message | | | From | "Rafael J. Wysocki" <> | Subject | Re: [PATCH -mm 2/2] PM: Disable usermode helper before hibernation and suspend | Date | Mon, 18 Jun 2007 17:15:14 +0200 |
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On Monday, 18 June 2007 12:51, Uli Luckas wrote: > On Sunday, 17. June 2007, you wrote: > > On Friday, 15 June 2007 23:36, Rafael J. Wysocki wrote: > > > On Friday, 15 June 2007 15:08, Uli Luckas wrote: > > > > On Monday, 4. June 2007, Rafael J. Wysocki wrote: > > > > > From: Rafael J. Wysocki <rjw@sisk.pl> > > > > > > > > > > Use a hibernation and suspend notifier to disable the user mode > > > > > helper before a hibernation/suspend and enable it after the > > > > > operation. > > > > > > > > Hi Rafael, > > > > I have a couple of questions, regarding this patch ... > > > > > 2) how does your patch prevent wait_for_completion(&done) to hang > > > > during freezing if usermodehelper_pm_callback is called _after_ the > > > > above check? > > > > > > It doesn't. Once the helper is running, we can't distinguish it from any > > > other user land process. > > > > > > Still, it narrows the window quite a bit. > > > > Okay, I think we can help it a bit. Please tell me what you think of the > > following patch (on top of 2.6.22-rc4-mm2). > > > Hi Rafael, > Thanks for your work. I haven't found the time to actually test your patch but > in general it looks like a valid aproach. > I think there is one problem though. You need to have your wait queue woken up > when you update (atomic_dec) running_helpers. Otherwise you end up always > waiting the full RUNNING_HELPERS_TIMEOUT.
Yeah, right. I tend to forget about obvious things. :-(
Besides, I think that the _pm_callback need not be compiled if CONFIG_PM is unset. If you can, please have a look at the next version of the patch (appended).
Greetings, Rafael
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl> --- kernel/kmod.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++++-------- 1 file changed, 66 insertions(+), 10 deletions(-)
Index: linux-2.6.22-rc4-mm2/kernel/kmod.c =================================================================== --- linux-2.6.22-rc4-mm2.orig/kernel/kmod.c +++ linux-2.6.22-rc4-mm2/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 /* @@ -275,6 +267,30 @@ static void __call_usermodehelper(struct } } +#ifdef CONFIG_PM +/* + * If set and if call_usermodehelper_exec() is supposed to wait, it 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) @@ -283,7 +299,15 @@ static int usermodehelper_pm_callback(st case PM_HIBERNATION_PREPARE: case PM_SUSPEND_PREPARE: usermodehelper_disabled = 1; - return NOTIFY_OK; + wait_event_timeout(running_helpers_waitq, + atomic_read(&running_helpers) == 0, + RUNNING_HELPERS_TIMEOUT); + if (atomic_read(&running_helpers) == 0) { + return NOTIFY_OK; + } else { + usermodehelper_disabled = 0; + return NOTIFY_BAD; + } case PM_POST_HIBERNATION: case PM_POST_SUSPEND: usermodehelper_disabled = 0; @@ -293,6 +317,36 @@ static int usermodehelper_pm_callback(st return NOTIFY_DONE; } +static void new_helper(void) +{ + atomic_inc(&running_helpers); +} + +static void helper_finished(void) +{ + if (atomic_dec_and_test(&running_helpers)) + wake_up(&running_helpers_waitq); +} + +#else /* CONFIG_PM */ +#define usermodehelper_disabled 0 + +static inline int usermodehelper_pm_callback(struct notifier_block *nfb, + unsigned long action, + void *ignored) +{ + return 0; +} + +static inline void new_helper(void) +{ +} + +static inline void helper_finished(void) +{ +} +#endif /* CONFIG_PM */ + /** * call_usermodehelper_setup - prepare to call a usermode helper * @path - path to usermode executable @@ -397,12 +451,13 @@ int call_usermodehelper_exec(struct subp DECLARE_COMPLETION_ONSTACK(done); int retval; + new_helper(); if (sub_info->path[0] == '\0') { retval = 0; goto out; } - if (!khelper_wq || usermodehelper_disabled) { + if (!khelper_wq || (wait != UMH_NO_WAIT && usermodehelper_disabled)) { retval = -EBUSY; goto out; } @@ -418,6 +473,7 @@ int call_usermodehelper_exec(struct subp out: call_usermodehelper_freeinfo(sub_info); + helper_finished(); return retval; } EXPORT_SYMBOL(call_usermodehelper_exec); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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