[S390] fix tlb flushing vs. concurrent /proc accesses

The tlb flushing code uses the mm_users field of the mm_struct to
decide if each page table entry needs to be flushed individually with
IPTE or if a global flush for the mm_struct is sufficient after all page
table updates have been done. The comment for mm_users says "How many
users with user space?" but the /proc code increases mm_users after it
found the process structure by pid without creating a new user process.
Which makes mm_users useless for the decision between the two tlb
flusing methods. The current code can be confused to not flush tlb
entries by a concurrent access to /proc files if e.g. a fork is in
progres. The solution for this problem is to make the tlb flushing
logic independent from the mm_users field.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c
index 541053ed234e..8127ebd59c4d 100644
--- a/arch/s390/kernel/smp.c
+++ b/arch/s390/kernel/smp.c
@@ -583,6 +583,7 @@ int __cpuinit __cpu_up(unsigned int cpu)
 	sf->gprs[9] = (unsigned long) sf;
 	cpu_lowcore->save_area[15] = (unsigned long) sf;
 	__ctl_store(cpu_lowcore->cregs_save_area, 0, 15);
+	atomic_inc(&init_mm.context.attach_count);
 	asm volatile(
 		"	stam	0,15,0(%0)"
 		: : "a" (&cpu_lowcore->access_regs_save_area) : "memory");
@@ -659,6 +660,7 @@ void __cpu_die(unsigned int cpu)
 	while (sigp_p(0, cpu, sigp_set_prefix) == sigp_busy)
 		udelay(10);
 	smp_free_lowcore(cpu);
+	atomic_dec(&init_mm.context.attach_count);
 	pr_info("Processor %d stopped\n", cpu);
 }