powerpc/mm: Fixup preempt underflow with huge pages

hugepd_free() used __get_cpu_var() once. Nothing ensured that the code
accessing the variable did not migrate from one CPU to another and soon
this was noticed by Tiejun Chen in 94b09d755462 ("powerpc/hugetlb:
Replace __get_cpu_var with get_cpu_var"). So we had it fixed.

Christoph Lameter was doing his __get_cpu_var() replaces and forgot
PowerPC. Then he noticed this and sent his fixed up batch again which
got applied as 69111bac42f5 ("powerpc: Replace __get_cpu_var uses").

The careful reader will noticed one little detail: get_cpu_var() got
replaced with this_cpu_ptr(). So now we have a put_cpu_var() which does
a preempt_enable() and nothing that does preempt_disable() so we
underflow the preempt counter.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: stable@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index 6dd272b6196f35b2644131ee5cbe94ddc25fd652..d991b9e80dbbc75ef955c78c924c2e273228b70f 100644 (file)
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -413,13 +413,13 @@ static void hugepd_free(struct mmu_gather *tlb, void *hugepte)
 {
        struct hugepd_freelist **batchp;
 
-       batchp = this_cpu_ptr(&hugepd_freelist_cur);
+       batchp = &get_cpu_var(hugepd_freelist_cur);
 
        if (atomic_read(&tlb->mm->mm_users) < 2 ||
            cpumask_equal(mm_cpumask(tlb->mm),
                          cpumask_of(smp_processor_id()))) {
                kmem_cache_free(hugepte_cache, hugepte);
-        put_cpu_var(hugepd_freelist_cur);
+               put_cpu_var(hugepd_freelist_cur);
                return;
        }