From: Andrew Morton <akpm@linux-foundation.org>

A series of patches which

- removes all but one callers of work_on_cpu() by switching them to
  smp_call_function_single()

- converts work_on_cpu() to create a kernel thread on demand, thus
  avoiding the various deadlock scenarios which we keep on experiencing and
  thinking up.

All cheerfully untested.


This patch:

Atttempting to rid us of the problematic work_on_cpu().  Just use
smp_call_fuction_single() here.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Cc: Len Brown <len.brown@intel.com>
Cc: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
 arch/x86/kernel/acpi/cstate.c |   36 ++++++++++++++++++++++++------------
 1 file changed, 24 insertions(+), 12 deletions(-)

diff -puN arch/x86/kernel/acpi/cstate.c~arch-x86-kernel-acpi-cstatec-avoid-using-work_on_cpu arch/x86/kernel/acpi/cstate.c
--- a/arch/x86/kernel/acpi/cstate.c~arch-x86-kernel-acpi-cstatec-avoid-using-work_on_cpu
+++ a/arch/x86/kernel/acpi/cstate.c
@@ -61,6 +61,12 @@ struct cstate_entry {
 };
 static struct cstate_entry *cpu_cstate_entry;	/* per CPU ptr */
 
+/* Used for the cross-CPU calls */
+struct acpi_processor_cx_cross_cpu {
+	struct acpi_processor_cx *cx;
+	long retval;
+};
+
 static short mwait_supported[ACPI_PROCESSOR_MAX_POWER];
 
 #define MWAIT_SUBSTATE_MASK	(0xf)
@@ -75,10 +81,10 @@ static short mwait_supported[ACPI_PROCES
 
 #define NATIVE_CSTATE_BEYOND_HALT	(2)
 
-static long acpi_processor_ffh_cstate_probe_cpu(void *_cx)
+static void acpi_processor_ffh_cstate_probe_cpu(void *_cxcc)
 {
-	struct acpi_processor_cx *cx = _cx;
-	long retval;
+	struct acpi_processor_cx_cross_cpu *cxcc = _cxcc;
+	struct acpi_processor_cx *cx = cxcc->cx;
 	unsigned int eax, ebx, ecx, edx;
 	unsigned int edx_part;
 	unsigned int cstate_type; /* C-state type and not ACPI C-state type */
@@ -92,16 +98,16 @@ static long acpi_processor_ffh_cstate_pr
 	edx_part = edx >> (cstate_type * MWAIT_SUBSTATE_SIZE);
 	num_cstate_subtype = edx_part & MWAIT_SUBSTATE_MASK;
 
-	retval = 0;
+	cxcc->retval = 0;
 	if (num_cstate_subtype < (cx->address & MWAIT_SUBSTATE_MASK)) {
-		retval = -1;
+		cxcc->retval = -1;
 		goto out;
 	}
 
 	/* mwait ecx extensions INTERRUPT_BREAK should be supported for C2/C3 */
 	if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED) ||
 	    !(ecx & CPUID5_ECX_INTERRUPT_BREAK)) {
-		retval = -1;
+		cxcc->retval = -1;
 		goto out;
 	}
 
@@ -115,7 +121,7 @@ static long acpi_processor_ffh_cstate_pr
 			ACPI_CX_DESC_LEN, "ACPI FFH INTEL MWAIT 0x%x",
 			cx->address);
 out:
-	return retval;
+	return;
 }
 
 int acpi_processor_ffh_cstate_probe(unsigned int cpu,
@@ -123,6 +129,7 @@ int acpi_processor_ffh_cstate_probe(unsi
 {
 	struct cstate_entry *percpu_entry;
 	struct cpuinfo_x86 *c = &cpu_data(cpu);
+	struct acpi_processor_cx_cross_cpu cxcc = { .cx = cx, };
 	long retval;
 
 	if (!cpu_cstate_entry || c->cpuid_level < CPUID_MWAIT_LEAF)
@@ -135,13 +142,18 @@ int acpi_processor_ffh_cstate_probe(unsi
 	percpu_entry->states[cx->index].eax = 0;
 	percpu_entry->states[cx->index].ecx = 0;
 
-	/* Make sure we are running on right CPU */
+	/* Run acpi_processor_ffh_cstate_probe_cpu() on the target CPU */
 
-	retval = work_on_cpu(cpu, acpi_processor_ffh_cstate_probe_cpu, cx);
+	retval = smp_call_function_single(cpu,
+				acpi_processor_ffh_cstate_probe_cpu, cx, 1);
 	if (retval == 0) {
-		/* Use the hint in CST */
-		percpu_entry->states[cx->index].eax = cx->address;
-		percpu_entry->states[cx->index].ecx = MWAIT_ECX_INTERRUPT_BREAK;
+		retval = cxcc.retval;
+		if (retval == 0) {
+			/* Use the hint in CST */
+			percpu_entry->states[cx->index].eax = cx->address;
+			percpu_entry->states[cx->index].ecx =
+					MWAIT_ECX_INTERRUPT_BREAK;
+		}
 	}
 	return retval;
 }
_