Commit 5aec788a authored by Peter Zijlstra's avatar Peter Zijlstra
Browse files

sched: Fix TASK_state comparisons 



Task state is fundamentally a bitmask; direct comparisons are probably
not working as intended. Specifically the normal wait-state have
a number of possible modifiers:

  TASK_UNINTERRUPTIBLE:	TASK_WAKEKILL, TASK_NOLOAD, TASK_FREEZABLE
  TASK_INTERRUPTIBLE:   TASK_FREEZABLE

Specifically, the addition of TASK_FREEZABLE wrecked
__wait_is_interruptible(). This however led to an audit of direct
comparisons yielding the rest of the changes.

Fixes: f5d39b02 ("freezer,sched: Rewrite core freezer logic")
Reported-by: default avatarChristian Borntraeger <borntraeger@linux.ibm.com>
Debugged-by: default avatarChristian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: default avatarChristian Borntraeger <borntraeger@linux.ibm.com>
parent 7e9518ba

include/linux/wait.h

+1 −1
Original line number Diff line number Diff line
@@ -281,7 +281,7 @@ static inline void wake_up_pollfree(struct wait_queue_head *wq_head) 


#define ___wait_is_interruptible(state)						\

	(!__builtin_constant_p(state) ||					\

		state == TASK_INTERRUPTIBLE || state == TASK_KILLABLE)		\

	 (state & (TASK_INTERRUPTIBLE | TASK_WAKEKILL)))



extern void init_wait_entry(struct wait_queue_entry *wq_entry, int flags);

kernel/hung_task.c

+6 −2
Original line number Diff line number Diff line
@@ -191,6 +191,8 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout) 
	hung_task_show_lock = false;

	rcu_read_lock();

	for_each_process_thread(g, t) {

		unsigned int state;



		if (!max_count--)

			goto unlock;

		if (time_after(jiffies, last_break + HUNG_TASK_LOCK_BREAK)) {
@@ -198,8 +200,10 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout) 
				goto unlock;

			last_break = jiffies;

		}

		/* use "==" to skip the TASK_KILLABLE tasks waiting on NFS */

		if (READ_ONCE(t->__state) == TASK_UNINTERRUPTIBLE)

		/* skip the TASK_KILLABLE tasks -- these can be killed */

		state = READ_ONCE(t->__state);

		if ((state & TASK_UNINTERRUPTIBLE) &&

		    !(state & TASK_WAKEKILL))

			check_hung_task(t, timeout);

	}

 unlock:

kernel/sched/core.c

+1 −1
Original line number Diff line number Diff line
@@ -8884,7 +8884,7 @@ state_filter_match(unsigned long state_filter, struct task_struct *p) 
	 * When looking for TASK_UNINTERRUPTIBLE skip TASK_IDLE (allows

	 * TASK_KILLABLE).

	 */

	if (state_filter == TASK_UNINTERRUPTIBLE && state == TASK_IDLE)

	if (state_filter == TASK_UNINTERRUPTIBLE && (state & TASK_NOLOAD))

		return false;



	return true;