+ lib-irq_poll-add-local_bh_disable-in-irq_poll_cpu_dead.patch added to -mm tree

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: lib/irq_poll: Add local_bh_disable() in irq_poll_cpu_dead()
has been added to the -mm tree.  Its filename is
     lib-irq_poll-add-local_bh_disable-in-irq_poll_cpu_dead.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/lib-irq_poll-add-local_bh_disable-in-irq_poll_cpu_dead.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/lib-irq_poll-add-local_bh_disable-in-irq_poll_cpu_dead.patch

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------------------------------------------------------
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: lib/irq_poll: Add local_bh_disable() in irq_poll_cpu_dead()

irq_poll_cpu_dead() pulls the blk_cpu_iopoll backlog from the dead CPU and
raises the POLL softirq with __raise_softirq_irqoff() on the CPU it is
running on.  That just sets the bit in the pending softirq mask.

This means the handling of the softirq is delayed until the next interrupt
or a local_bh_disable/enable() pair.  As a consequence the CPU on which
this code runs can reach idle with the POLL softirq pending, which
triggers a warning in the NOHZ idle code.

Add a local_bh_disable/enable() pair around the interrupts disabled
section in irq_poll_cpu_dead().  local_bh_enable will handle the pending
softirq.

[@linutronix.de: massaged changelog and comment]
Link: https://lkml.kernel.org/r/87k0bxgl27.ffs@tglx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---


--- a/lib/irq_poll.c~lib-irq_poll-add-local_bh_disable-in-irq_poll_cpu_dead
+++ a/lib/irq_poll.c
@@ -188,14 +188,18 @@ EXPORT_SYMBOL(irq_poll_init);
 static int irq_poll_cpu_dead(unsigned int cpu)
 {
 	/*
-	 * If a CPU goes away, splice its entries to the current CPU
-	 * and trigger a run of the softirq
+	 * If a CPU goes away, splice its entries to the current CPU and
+	 * set the POLL softirq bit. The local_bh_disable()/enable() pair
+	 * ensures that it is handled. Otherwise the current CPU could
+	 * reach idle with the POLL softirq pending.
 	 */
+	local_bh_disable();
 	local_irq_disable();
 	list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
 			 this_cpu_ptr(&blk_cpu_iopoll));
 	__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
 	local_irq_enable();
+	local_bh_enable();
 
 	return 0;
 }
_

Patches currently in -mm which might be from bigeasy@linutronix.de are

lib-irq_poll-add-local_bh_disable-in-irq_poll_cpu_dead.patch