tick/rcu: Fix false positive "softirq work is pending" messages

[ Upstream commit 96c1fa0 ]

In commit 0345691 ("tick/rcu: Stop allowing RCU_SOFTIRQ in idle") the
new function report_idle_softirq() was created by breaking code out of the
existing can_stop_idle_tick() for kernels v5.18 and newer.

In doing so, the code essentially went from a one conditional:

	if (a && b && c)
		warn();

to a three conditional:

	if (!a)
		return;
	if (!b)
		return;
	if (!c)
		return;
	warn();

But that conversion got the condition for the RT specific
local_bh_blocked() wrong. The original condition was:

   	!local_bh_blocked()

but the conversion failed to negate it so it ended up as:

        if (!local_bh_blocked())
		return false;

This issue lay dormant until another fixup for the same commit was added
in commit a7e282c ("tick/rcu: Fix bogus ratelimit condition").
This commit realized the ratelimit was essentially set to zero instead
of ten, and hence *no* softirq pending messages would ever be issued.

Once this commit was backported via linux-stable, both the v6.1 and v6.4
preempt-rt kernels started printing out 10 instances of this at boot:

  NOHZ tick-stop error: local softirq work is pending, handler #80!!!

Remove the negation and return when local_bh_blocked() evaluates to true to
bring the correct behaviour back.

Fixes: 0345691 ("tick/rcu: Stop allowing RCU_SOFTIRQ in idle")
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Reviewed-by: Wen Yang <wenyang.linux@foxmail.com>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20230818200757.1808398-1-paul.gortmaker@windriver.com
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: Paul Gortmaker

kernel/time/tick-sched.c

@@ -1050,7 +1050,7 @@ static bool report_idle_softirq(void)
 		return false;
 
 	/* On RT, softirqs handling may be waiting on some lock */
-	if (!local_bh_blocked())
+	if (local_bh_blocked())
 		return false;
 
 	pr_warn("NOHZ tick-stop error: local softirq work is pending, handler #%02x!!!\n",