linux-kernel - [PATCH 5.10 007/102] sched/core: Allow try_invoke_on_locked_down

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Date:   Fri,  5 Mar 2021 13:20:26 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+cb3b69ae80afd6535b0e@...kaller.appspotmail.com,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH 5.10 007/102] sched/core: Allow try_invoke_on_locked_down_task() with irqs disabled

From: Peter Zijlstra <peterz@...radead.org>

commit 1b7af295541d75535374325fd617944534853919 upstream.

The try_invoke_on_locked_down_task() function currently requires
that interrupts be enabled, but it is called with interrupts
disabled from rcu_print_task_stall(), resulting in an "IRQs not
enabled as expected" diagnostic.  This commit therefore updates
try_invoke_on_locked_down_task() to use raw_spin_lock_irqsave() instead
of raw_spin_lock_irq(), thus allowing use from either context.

Link: https://lore.kernel.org/lkml/000000000000903d5805ab908fc4@google.com/
Link: https://lore.kernel.org/lkml/20200928075729.GC2611@hirez.programming.kicks-ass.net/
Reported-by: syzbot+cb3b69ae80afd6535b0e@...kaller.appspotmail.com
Signed-off-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 kernel/sched/core.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2989,7 +2989,7 @@ out:
 
 /**
  * try_invoke_on_locked_down_task - Invoke a function on task in fixed state
- * @p: Process for which the function is to be invoked.
+ * @p: Process for which the function is to be invoked, can be @current.
  * @func: Function to invoke.
  * @arg: Argument to function.
  *
@@ -3007,12 +3007,11 @@ out:
  */
 bool try_invoke_on_locked_down_task(struct task_struct *p, bool (*func)(struct task_struct *t, void *arg), void *arg)
 {
-	bool ret = false;
 	struct rq_flags rf;
+	bool ret = false;
 	struct rq *rq;
 
-	lockdep_assert_irqs_enabled();
-	raw_spin_lock_irq(&p->pi_lock);
+	raw_spin_lock_irqsave(&p->pi_lock, rf.flags);
 	if (p->on_rq) {
 		rq = __task_rq_lock(p, &rf);
 		if (task_rq(p) == rq)
@@ -3029,7 +3028,7 @@ bool try_invoke_on_locked_down_task(stru
 				ret = func(p, arg);
 		}
 	}
-	raw_spin_unlock_irq(&p->pi_lock);
+	raw_spin_unlock_irqrestore(&p->pi_lock, rf.flags);
 	return ret;
 }