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[PATCH] x86/intel_rdt.c: Disable preempt for intel_rdt_sched_in() in move_myself()

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

intel_rdt_sched_in() calls this_cpu_ptr() read and write pqr_state and
update PQR_ASSOC on current cpu. If execution of the function is preempted
and switched to another CPU, the results are wrong. If 
CONFIG_DEBUG_PREEMPT is turned on, the issue is reported as
"BUG: smp_processor_id() running in preemptible code." when moving a task
to a rdtgroup in move_myself().

Disable preempt before intel_rdt_sched_in() and eanble preempt after
the function in move_myself() to solve the issue.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
---
 arch/x86/kernel/cpu/intel_rdt_rdtgroup.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/include/asm/intel_rdt.h b/arch/x86/include/asm/intel_rdt.h
index 6e90e87..eaaa765 100644
--- a/arch/x86/include/asm/intel_rdt.h
+++ b/arch/x86/include/asm/intel_rdt.h
@@ -192,6 +192,9 @@ 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.
+ * - Caller needs to disable preempt before calling this function.
+ *   The function doesn't check preemptible. Scheduler hot path
+ *   disables preempt already.
  */
 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..9c6f732 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);
 	}
 
+	get_cpu();
 	/* update PQR_ASSOC MSR to make resource group go into effect */
 	intel_rdt_sched_in();
+	put_cpu();
 
 	kfree(callback);
 }

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[PATCH] x86/intel_rdt.c: Disable preempt for intel_rdt_sched_in() in move_myself() "Fenghua Yu" <fenghua.yu@intel.com> - 2016-11-30 22:50 +0100
  Re: [PATCH] x86/intel_rdt.c: Disable preempt for intel_rdt_sched_in()  in move_myself() Thomas Gleixner <tglx@linutronix.de> - 2016-11-30 23:20 +0100

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