Add a comment explaining part of the logic for mm_cpumask trimming, and
add a (hopefully graceful) check and warning in case something gets it
wrong.
Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
arch/powerpc/mm/book3s64/radix_tlb.c | 27 +++++++++++++++++++++------
1 file changed, 21 insertions(+), 6 deletions(-)
diff --git a/arch/powerpc/mm/book3s64/radix_tlb.c
b/arch/powerpc/mm/book3s64/radix_tlb.c
index b487b489d4b6..5f09e0cd0016 100644
--- a/arch/powerpc/mm/book3s64/radix_tlb.c
+++ b/arch/powerpc/mm/book3s64/radix_tlb.c
@@ -644,13 +644,14 @@ static void do_exit_flush_lazy_tlb(void *arg)
{
struct mm_struct *mm = arg;
unsigned long pid = mm->context.id;
+ int cpu = smp_processor_id();
/*
* A kthread could have done a mmget_not_zero() after the flushing CPU
- * checked mm_is_singlethreaded, and be in the process of
- * kthread_use_mm when interrupted here. In that case, current->mm will
- * be set to mm, because kthread_use_mm() setting ->mm and switching to
- * the mm is done with interrupts off.
+ * checked mm_cpumask, and be in the process of kthread_use_mm when
+ * interrupted here. In that case, current->mm will be set to mm,
+ * because kthread_use_mm() setting ->mm and switching to the mm is
+ * done with interrupts off.
*/
if (current->mm == mm)
goto out_flush;
@@ -664,8 +665,22 @@ static void do_exit_flush_lazy_tlb(void *arg)
mmdrop(mm);
}
- atomic_dec(&mm->context.active_cpus);
- cpumask_clear_cpu(smp_processor_id(), mm_cpumask(mm));
+ /*
+ * This IPI is only initiated from a CPU which is running mm which
+ * is a single-threaded process, so there will not be another racing
+ * IPI coming in where we would find our cpumask already clear.
+ *
+ * Nothing else clears our bit in the cpumask except CPU offlining,
+ * in which case we should not be taking IPIs here. However check
+ * this just in case the logic is wrong somewhere, and don't underflow
+ * the active_cpus count.
+ */
+ if (cpumask_test_cpu(cpu, mm_cpumask(mm))) {
+ atomic_dec(&mm->context.active_cpus);
+ cpumask_clear_cpu(cpu, mm_cpumask(mm));
+ } else {
+ WARN_ON_ONCE(1);
+ }
out_flush:
_tlbiel_pid(pid, RIC_FLUSH_ALL);
--
2.23.0
