linux-kernel - [tip: sched/core] sched: Fix TASK

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Date:   Wed, 28 Sep 2022 06:57:32 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Christian Borntraeger <borntraeger@...ux.ibm.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/core] sched: Fix TASK_state comparisons

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     543f82fee0c531c8386f776a6050878a5bfe96f4
Gitweb:        https://git.kernel.org/tip/543f82fee0c531c8386f776a6050878a5bfe96f4
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Tue, 27 Sep 2022 21:02:34 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 27 Sep 2022 22:50:22 +02:00

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: f5d39b020809 ("freezer,sched: Rewrite core freezer logic")
Reported-by: Christian Borntraeger <borntraeger@...ux.ibm.com>
Debugged-by: Christian Borntraeger <borntraeger@...ux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Christian Borntraeger <borntraeger@...ux.ibm.com>
---
 include/linux/wait.h | 2 +-
 kernel/hung_task.c   | 8 ++++++--
 kernel/sched/core.c  | 2 +-
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/include/linux/wait.h b/include/linux/wait.h
index 14ad8a0..7f5a51a 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -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);
 
diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index f1321c0..4a8a713 100644
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -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:
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4fa4a3d..02dc1b8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -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;