[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, 5 insertions, 1 deletions

diff --git a/arch/s390/include/asm/tlbflush.h b/arch/s390/include/asm/tlbflush.h
index 304cffa623e1..29d5d6d4becc 100644
--- a/arch/s390/include/asm/tlbflush.h
+++ b/arch/s390/include/asm/tlbflush.h
@@ -94,8 +94,12 @@ static inline void __tlb_flush_mm(struct mm_struct * mm)
 
 static inline void __tlb_flush_mm_cond(struct mm_struct * mm)
 {
-        if (atomic_read(&mm->mm_users) <= 1 && mm == current->active_mm)
+        spin_lock(&mm->page_table_lock);
+        if (mm->context.flush_mm) {
                 __tlb_flush_mm(mm);
+                mm->context.flush_mm = 0;
+        }
+        spin_unlock(&mm->page_table_lock);
 }
 
 /*