linux-kernel - [PATCH 3.16 34/72] powerpc/pseries: correctly track irq state in default idle

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Message-ID: <lsq.1575813165.714960861@decadent.org.uk>
Date:   Sun, 08 Dec 2019 13:53:18 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Michael Ellerman" <mpe@...erman.id.au>,
        "Nathan Lynch" <nathanl@...ux.ibm.com>
Subject: [PATCH 3.16 34/72] powerpc/pseries: correctly track irq state in
 default idle

3.16.79-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Nathan Lynch <nathanl@...ux.ibm.com>

commit 92c94dfb69e350471473fd3075c74bc68150879e upstream.

prep_irq_for_idle() is intended to be called before entering
H_CEDE (and it is used by the pseries cpuidle driver). However the
default pseries idle routine does not call it, leading to mismanaged
lazy irq state when the cpuidle driver isn't in use. Manifestations of
this include:

* Dropped IPIs in the time immediately after a cpu comes
  online (before it has installed the cpuidle handler), making the
  online operation block indefinitely waiting for the new cpu to
  respond.

* Hitting this WARN_ON in arch_local_irq_restore():
	/*
	 * We should already be hard disabled here. We had bugs
	 * where that wasn't the case so let's dbl check it and
	 * warn if we are wrong. Only do that when IRQ tracing
	 * is enabled as mfmsr() can be costly.
	 */
	if (WARN_ON_ONCE(mfmsr() & MSR_EE))
		__hard_irq_disable();

Call prep_irq_for_idle() from pseries_lpar_idle() and honor its
result.

Fixes: 363edbe2614a ("powerpc: Default arch idle could cede processor on pseries")
Signed-off-by: Nathan Lynch <nathanl@...ux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@...erman.id.au>
Link: https://lore.kernel.org/r/20190910225244.25056-1-nathanl@linux.ibm.com
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 arch/powerpc/platforms/pseries/setup.c | 3 +++
 1 file changed, 3 insertions(+)

--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -360,6 +360,9 @@ static void pseries_lpar_idle(void)
 	 * low power mode by cedeing processor to hypervisor
 	 */
 
+	if (!prep_irq_for_idle())
+		return;
+
 	/* Indicate to hypervisor that we are idle. */
 	get_lppaca()->idle = 1;