[RFC PATCH 3/6] alpha: remove TLB flushing mm_users special case

[Nicholas Piggin <npiggin@gmail.com>]

With mm_cpumask, there is less reason to keep the mm_users special case
in the TLB flushing code, because IPIs will be filtered out by the mask.

These special cases are another complicated set of races e.g., vs
kthread_use_mm that make this code tricky to reason about.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/alpha/kernel/smp.c | 68 +++++++++--------------------------------
 1 file changed, 15 insertions(+), 53 deletions(-)

diff --git a/arch/alpha/kernel/smp.c b/arch/alpha/kernel/smp.c
index b702372fbaba..e436c056267d 100644
--- a/arch/alpha/kernel/smp.c
+++ b/arch/alpha/kernel/smp.c
@@ -639,23 +639,6 @@ ipi_flush_tlb_mm(void *x)
 void
 flush_tlb_mm(struct mm_struct *mm)
 {
-	preempt_disable();
-
-	if (mm == current->active_mm) {
-		flush_tlb_current(mm);
-		if (atomic_read(&mm->mm_users) <= 1) {
-			int cpu, this_cpu = smp_processor_id();
-			for (cpu = 0; cpu < NR_CPUS; cpu++) {
-				if (!cpu_online(cpu) || cpu == this_cpu)
-					continue;
-				if (mm->context[cpu])
-					mm->context[cpu] = 0;
-			}
-			preempt_enable();
-			return;
-		}
-	}
-
 	/*
 	 * TLB flush IPIs will be sent to all CPUs with mm_cpumask set. The
 	 * problem of ordering the load of mm_cpumask vs a CPU switching to
@@ -666,8 +649,12 @@ flush_tlb_mm(struct mm_struct *mm)
 	 * The other side is switch_mm.
 	 */
 	smp_mb();
+	preempt_disable();
+	if (mm == current->active_mm)
+		flush_tlb_current(mm);
+	else
+		flush_tlb_other(mm);
 	smp_call_function_many(mm_cpumask(mm), ipi_flush_tlb_mm, mm, 1);
-
 	preempt_enable();
 }
 EXPORT_SYMBOL(flush_tlb_mm);
@@ -696,30 +683,17 @@ flush_tlb_page(struct vm_area_struct *vma, unsigned long addr)
 	struct flush_tlb_page_struct data;
 	struct mm_struct *mm = vma->vm_mm;
 
-	preempt_disable();
-
-	if (mm == current->active_mm) {
-		flush_tlb_current_page(mm, vma, addr);
-		if (atomic_read(&mm->mm_users) <= 1) {
-			int cpu, this_cpu = smp_processor_id();
-			for (cpu = 0; cpu < NR_CPUS; cpu++) {
-				if (!cpu_online(cpu) || cpu == this_cpu)
-					continue;
-				if (mm->context[cpu])
-					mm->context[cpu] = 0;
-			}
-			preempt_enable();
-			return;
-		}
-	}
-
 	data.vma = vma;
 	data.mm = mm;
 	data.addr = addr;
 
 	smp_mb(); /* see flush_tlb_mm */
+	preempt_disable();
+	if (mm == current->active_mm)
+		flush_tlb_current_page(mm, vma, addr);
+	else
+		flush_tlb_other(mm);
 	smp_call_function_many(mm_cpumask(mm), ipi_flush_tlb_page, &data, 1);
-
 	preempt_enable();
 }
 EXPORT_SYMBOL(flush_tlb_page);
@@ -751,24 +725,12 @@ flush_icache_user_page(struct vm_area_struct *vma, struct page *page,
 	if ((vma->vm_flags & VM_EXEC) == 0)
 		return;
 
+	smp_mb(); /* see flush_tlb_mm */
 	preempt_disable();
-
-	if (mm == current->active_mm) {
+	if (mm == current->active_mm)
 		__load_new_mm_context(mm);
-		if (atomic_read(&mm->mm_users) <= 1) {
-			int cpu, this_cpu = smp_processor_id();
-			for (cpu = 0; cpu < NR_CPUS; cpu++) {
-				if (!cpu_online(cpu) || cpu == this_cpu)
-					continue;
-				if (mm->context[cpu])
-					mm->context[cpu] = 0;
-			}
-			preempt_enable();
-			return;
-		}
-	}
-
-	smp_call_function(ipi_flush_icache_page, mm, 1);
-
+	else
+		flush_tlb_other(mm);
+	smp_call_function_many(mm_cpumask(mm), ipi_flush_icache_page, mm, 1);
 	preempt_enable();
 }
-- 
2.40.1