Eric Lee / linux-smarc-t335x-v3.2

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Commit ccd4b65aef4be2278543fde5b999e55a4d694fd8

Authored by Rafael J. Wysocki
Committed by Linus Torvalds
1 parent 8cdd4936c1
Exists in master and in 4 other branches v3.2_AM335xPSP_04.06.00.11, v3.2_NEWT335xPSP_04.06.00.11, v3.2_SBC_SMARTMEN, v3.2_SMARCT335xPSP_04.06.00.11

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>

Showing 1 changed file with 68 additions and 10 deletions Side-by-side Diff

... ... @@ -41,14 +41,6 @@
41 41  
42 42 static struct workqueue_struct *khelper_wq;
43 43  
44   -/*
45   - * If set, both call_usermodehelper_keys() and call_usermodehelper_pipe() exit
46   - * immediately returning -EBUSY. Used for preventing user land processes from
47   - * being created after the user land has been frozen during a system-wide
48   - * hibernation or suspend operation.
49   - */
50   -static int usermodehelper_disabled;
51   -
52 44 #ifdef CONFIG_KMOD
53 45  
54 46 /*
55 47  
56 48  
... ... @@ -275,15 +267,55 @@
275 267 }
276 268 }
277 269  
  270 +#ifdef CONFIG_PM
  271 +/*
  272 + * If set, call_usermodehelper_exec() will exit immediately returning -EBUSY
  273 + * (used for preventing user land processes from being created after the user
  274 + * land has been frozen during a system-wide hibernation or suspend operation).
  275 + */
  276 +static int usermodehelper_disabled;
  277 +
  278 +/* Number of helpers running */
  279 +static atomic_t running_helpers = ATOMIC_INIT(0);
  280 +
  281 +/*
  282 + * Wait queue head used by usermodehelper_pm_callback() to wait for all running
  283 + * helpers to finish.
  284 + */
  285 +static DECLARE_WAIT_QUEUE_HEAD(running_helpers_waitq);
  286 +
  287 +/*
  288 + * Time to wait for running_helpers to become zero before the setting of
  289 + * usermodehelper_disabled in usermodehelper_pm_callback() fails
  290 + */
  291 +#define RUNNING_HELPERS_TIMEOUT (5 * HZ)
  292 +
278 293 static int usermodehelper_pm_callback(struct notifier_block *nfb,
279 294 unsigned long action,
280 295 void *ignored)
281 296 {
  297 + long retval;
  298 +
282 299 switch (action) {
283 300 case PM_HIBERNATION_PREPARE:
284 301 case PM_SUSPEND_PREPARE:
285 302 usermodehelper_disabled = 1;
286   - return NOTIFY_OK;
  303 + smp_mb();
  304 + /*
  305 + * From now on call_usermodehelper_exec() won't start any new
  306 + * helpers, so it is sufficient if running_helpers turns out to
  307 + * be zero at one point (it may be increased later, but that
  308 + * doesn't matter).
  309 + */
  310 + retval = wait_event_timeout(running_helpers_waitq,
  311 + atomic_read(&running_helpers) == 0,
  312 + RUNNING_HELPERS_TIMEOUT);
  313 + if (retval) {
  314 + return NOTIFY_OK;
  315 + } else {
  316 + usermodehelper_disabled = 0;
  317 + return NOTIFY_BAD;
  318 + }
287 319 case PM_POST_HIBERNATION:
288 320 case PM_POST_SUSPEND:
289 321 usermodehelper_disabled = 0;
... ... @@ -293,6 +325,30 @@
293 325 return NOTIFY_DONE;
294 326 }
295 327  
  328 +static void helper_lock(void)
  329 +{
  330 + atomic_inc(&running_helpers);
  331 + smp_mb__after_atomic_inc();
  332 +}
  333 +
  334 +static void helper_unlock(void)
  335 +{
  336 + if (atomic_dec_and_test(&running_helpers))
  337 + wake_up(&running_helpers_waitq);
  338 +}
  339 +
  340 +static void register_pm_notifier_callback(void)
  341 +{
  342 + pm_notifier(usermodehelper_pm_callback, 0);
  343 +}
  344 +#else /* CONFIG_PM */
  345 +#define usermodehelper_disabled 0
  346 +
  347 +static inline void helper_lock(void) {}
  348 +static inline void helper_unlock(void) {}
  349 +static inline void register_pm_notifier_callback(void) {}
  350 +#endif /* CONFIG_PM */
  351 +
296 352 /**
297 353 * call_usermodehelper_setup - prepare to call a usermode helper
298 354 * @path - path to usermode executable
... ... @@ -397,6 +453,7 @@
397 453 DECLARE_COMPLETION_ONSTACK(done);
398 454 int retval;
399 455  
  456 + helper_lock();
400 457 if (sub_info->path[0] == '\0') {
401 458 retval = 0;
402 459 goto out;
... ... @@ -418,6 +475,7 @@
418 475  
419 476 out:
420 477 call_usermodehelper_freeinfo(sub_info);
  478 + helper_unlock();
421 479 return retval;
422 480 }
423 481 EXPORT_SYMBOL(call_usermodehelper_exec);
... ... @@ -459,6 +517,6 @@
459 517 {
460 518 khelper_wq = create_singlethread_workqueue("khelper");
461 519 BUG_ON(!khelper_wq);
462   - pm_notifier(usermodehelper_pm_callback, 0);
  520 + register_pm_notifier_callback();
463 521 }