parisc: mm: don't count preallocated pmds

The patch dc6c9a35b66b520cf67e05d8ca60ebecad3b0479 that counts pmds
allocated for a process introduced a bug on 64-bit PA-RISC kernels.

The PA-RISC architecture preallocates one pmd with each pgd. This
preallocated pmd can never be freed - pmd_free does nothing when it is
called with this pmd. When the kernel attempts to free this preallocated
pmd, it decreases the count of allocated pmds. The result is that the
counter underflows and this error is reported.

This patch fixes the bug by artifically incrementing the counter in
pmd_free when the kernel tries to free the preallocated pmd.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Helge Deller <deller@gmx.de>

diff --git a/arch/parisc/include/asm/pgalloc.h b/arch/parisc/include/asm/pgalloc.h
index f213f5b..63e9eca 100644 (file)
--- a/arch/parisc/include/asm/pgalloc.h
+++ b/arch/parisc/include/asm/pgalloc.h
@@ -74,8 +74,13 @@ static inline void pmd_free(struct mm_struct *mm, pmd_t *pmd)
 {
 #ifdef CONFIG_64BIT
        if(pmd_flag(*pmd) & PxD_FLAG_ATTACHED)
-               /* This is the permanent pmd attached to the pgd;
-                * cannot free it */
+               /*
+                * This is the permanent pmd attached to the pgd;
+                * cannot free it.
+                * Increment the counter to compensate for the decrement
+                * done by generic mm code.
+                */
+               mm_inc_nr_pmds(mm);
                return;
 #endif
        free_pages((unsigned long)pmd, PMD_ORDER);