[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, 1 insertions, 2 deletions

diff --git a/arch/s390/include/asm/tlb.h b/arch/s390/include/asm/tlb.h
index 81150b05368..fd1c00d08bf 100644
--- a/arch/s390/include/asm/tlb.h
+++ b/arch/s390/include/asm/tlb.h
@@ -50,8 +50,7 @@ static inline struct mmu_gather *tlb_gather_mmu(struct mm_struct *mm,
 	struct mmu_gather *tlb = &get_cpu_var(mmu_gathers);
 
 	tlb->mm = mm;
-	tlb->fullmm = full_mm_flush || (num_online_cpus() == 1) ||
-		(atomic_read(&mm->mm_users) <= 1 && mm == current->active_mm);
+	tlb->fullmm = full_mm_flush;
 	tlb->nr_ptes = 0;
 	tlb->nr_pxds = TLB_NR_PTRS;
 	if (tlb->fullmm)