[PATCH 8/9] sparc32: retain mm_cpumask across TLB shootdowns

[Magnus Lindholm <linmag7@gmail.com>]

smp_flush_tlb_mm() narrows mm_cpumask to the current CPU when mm_users is
one and current->active_mm matches. That snapshot does not exclude another
task obtaining a reference with mmget_not_zero() and using the address
space through kthread_use_mm(). Clearing its CPU bit can make subsequent
shootdowns miss translations on that CPU. Testing current->mm instead does
not serialize against that race.

Remove the narrowing. This follows the SPARC64 fix in commit bafb056ce279
("sparc64: remove mm_cpumask clearing to fix kthread_use_mm race"). Retain
the accumulated CPU mask until normal address-space teardown.

A single-threaded mm that has migrated can consequently need remote
shootdowns for the remainder of its lifetime; sun4m broadcasts them to
online peers. This trades extra cross-calls for correct coverage.

Cc: stable@vger.kernel.org
Signed-off-by: Magnus Lindholm <linmag7@gmail.com>
---
 arch/sparc/mm/srmmu.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/arch/sparc/mm/srmmu.c b/arch/sparc/mm/srmmu.c
index aa53ec10cd8a..d3634bcb048d 100644
--- a/arch/sparc/mm/srmmu.c
+++ b/arch/sparc/mm/srmmu.c
@@ -1624,12 +1624,8 @@ static void smp_flush_cache_mm(struct mm_struct *mm)
 static void smp_flush_tlb_mm(struct mm_struct *mm)
 {
 	if (mm->context != NO_CONTEXT) {
-		if (any_other_mm_cpus(mm)) {
+		if (any_other_mm_cpus(mm))
 			xc1(local_ops->tlb_mm, (unsigned long)mm);
-			if (atomic_read(&mm->mm_users) == 1 && current->active_mm == mm)
-				cpumask_copy(mm_cpumask(mm),
-					     cpumask_of(smp_processor_id()));
-		}
 		local_ops->tlb_mm(mm);
 	}
 }
-- 
2.43.0