[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, 3 insertions, 1 deletions

diff --git a/arch/s390/include/asm/hugetlb.h b/arch/s390/include/asm/hugetlb.h
index 670a1d1745d2..bb8343d157bc 100644
--- a/arch/s390/include/asm/hugetlb.h
+++ b/arch/s390/include/asm/hugetlb.h
@@ -97,6 +97,7 @@ static inline pte_t huge_ptep_get_and_clear(struct mm_struct *mm,
 {
         pte_t pte = huge_ptep_get(ptep);
 
+        mm->context.flush_mm = 1;
         pmd_clear((pmd_t *) ptep);
         return pte;
 }
@@ -167,7 +168,8 @@ static inline void huge_ptep_invalidate(struct mm_struct *mm,
 ({                                                                      \
         pte_t __pte = huge_ptep_get(__ptep);                            \
         if (pte_write(__pte)) {                                         \
-                if (atomic_read(&(__mm)->mm_users) > 1 ||               \
+                (__mm)->context.flush_mm = 1;                           \
+                if (atomic_read(&(__mm)->context.attach_count) > 1 ||   \
                     (__mm) != current->active_mm)                       \
                         huge_ptep_invalidate(__mm, __addr, __ptep);     \
                 set_huge_pte_at(__mm, __addr, __ptep,                   \