linux-kernel - [PATCH v2] x86/intel_rdt: Call intel_rdt_sched

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Date:   Thu,  1 Dec 2016 12:55:14 -0800
From:   "Fenghua Yu" <fenghua.yu@...el.com>
To:     "Thomas Gleixner" <tglx@...utronix.de>
Cc:     "H. Peter Anvin" <h.peter.anvin@...el.com>,
        "Ingo Molnar" <mingo@...e.hu>,
        "Marcelo Tosatti" <mtosatti@...hat.com>,
        "Tony Luck" <tony.luck@...el.com>,
        "Ravi V Shankar" <ravi.v.shankar@...el.com>,
        "Sai Prakhya" <sai.praneeth.prakhya@...el.com>,
        "Vikas Shivappa" <vikas.shivappa@...ux.intel.com>,
        "linux-kernel" <linux-kernel@...r.kernel.org>,
        "x86" <x86@...nel.org>, "Fenghua Yu" <fenghua.yu@...el.com>
Subject: [PATCH v2] x86/intel_rdt: Call intel_rdt_sched_in() with preemption disabled

From: Fenghua Yu <fenghua.yu@...el.com>

intel_rdt_sched_in() must be called with preemption disabled because the
function accesses percpu variables (pqr_state and closid).

If a task moves itself via move_myself() preemption is enabled, which
violates the calling convention and can result in incorrect closid
selection when the task gets preempted or migrated.

Add the required protection and a comment about the calling convention.

Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
---
 arch/x86/include/asm/intel_rdt.h         | 2 ++
 arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/arch/x86/include/asm/intel_rdt.h b/arch/x86/include/asm/intel_rdt.h
index 6e90e87..95ce5c8 100644
--- a/arch/x86/include/asm/intel_rdt.h
+++ b/arch/x86/include/asm/intel_rdt.h
@@ -192,6 +192,8 @@ int rdtgroup_schemata_show(struct kernfs_open_file *of,
  *   resctrl file system.
  * - Caches the per cpu CLOSid values and does the MSR write only
  *   when a task with a different CLOSid is scheduled in.
+ *
+ * Must be called with preemption disabled.
  */
 static inline void intel_rdt_sched_in(void)
 {
diff --git a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
index fb8e03e..1afd3f3 100644
--- a/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
+++ b/arch/x86/kernel/cpu/intel_rdt_rdtgroup.c
@@ -326,8 +326,10 @@ static void move_myself(struct callback_head *head)
 		kfree(rdtgrp);
 	}
 
+	preempt_disable();
 	/* update PQR_ASSOC MSR to make resource group go into effect */
 	intel_rdt_sched_in();
+	preempt_enable();
 
 	kfree(callback);
 }
-- 
2.5.0