mm: fix false-positive warning on exit due mm_nr_pmds(mm)
The problem is that we check nr_ptes/nr_pmds in exit_mmap() which happens
*before* pgd_free(). And if an arch does pte/pmd allocation in
pgd_alloc() and frees them in pgd_free() we see offset in counters by the
time of the checks.
We tried to workaround this by offsetting expected counter value according
to FIRST_USER_ADDRESS for both nr_pte and nr_pmd in exit_mmap(). But it
doesn't work in some cases:
1. ARM with LPAE enabled also has non-zero USER_PGTABLES_CEILING, but
upper addresses occupied with huge pmd entries, so the trick with
offsetting expected counter value will get really ugly: we will have
to apply it nr_pmds, but not nr_ptes.
2. Metag has non-zero FIRST_USER_ADDRESS, but doesn't do allocation
pte/pmd page tables allocation in pgd_alloc(), just setup a pgd entry
which is allocated at boot and shared accross all processes.
The proposal is to move the check to check_mm() which happens *after*
pgd_free() and do proper accounting during pgd_alloc() and pgd_free()
which would bring counters to zero if nothing leaked.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Tyler Baker <tyler.baker@linaro.org>
Tested-by: Tyler Baker <tyler.baker@linaro.org>
Tested-by: Nishanth Menon <nm@ti.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/arm/mm/pgd.c b/arch/arm/mm/pgd.c
index 2493795..a3681f1 100644
--- a/arch/arm/mm/pgd.c
+++ b/arch/arm/mm/pgd.c
@@ -97,6 +97,7 @@
no_pte:
pmd_free(mm, new_pmd);
+ mm_dec_nr_pmds(mm);
no_pmd:
pud_free(mm, new_pud);
no_pud:
@@ -130,9 +131,11 @@
pte = pmd_pgtable(*pmd);
pmd_clear(pmd);
pte_free(mm, pte);
+ atomic_long_dec(&mm->nr_ptes);
no_pmd:
pud_clear(pud);
pmd_free(mm, pmd);
+ mm_dec_nr_pmds(mm);
no_pud:
pgd_clear(pgd);
pud_free(mm, pud);
@@ -152,6 +155,7 @@
pmd = pmd_offset(pud, 0);
pud_clear(pud);
pmd_free(mm, pmd);
+ mm_dec_nr_pmds(mm);
pgd_clear(pgd);
pud_free(mm, pud);
}