sched/preempt, mm/kmap: Explicitly disable/enable preemption in kmap_atomic_*

The existing code relies on pagefault_disable() implicitly disabling
preemption, so that no schedule will happen between kmap_atomic() and
kunmap_atomic().

Let's make this explicit, to prepare for pagefault_disable() not
touching preemption anymore.

Reviewed-and-tested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: David.Laight@ACULAB.COM
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: airlied@linux.ie
Cc: akpm@linux-foundation.org
Cc: benh@kernel.crashing.org
Cc: bigeasy@linutronix.de
Cc: borntraeger@de.ibm.com
Cc: daniel.vetter@intel.com
Cc: heiko.carstens@de.ibm.com
Cc: herbert@gondor.apana.org.au
Cc: hocko@suse.cz
Cc: hughd@google.com
Cc: mst@redhat.com
Cc: paulus@samba.org
Cc: ralf@linux-mips.org
Cc: schwidefsky@de.ibm.com
Cc: yang.shi@windriver.com
Link: http://lkml.kernel.org/r/1431359540-32227-5-git-send-email-dahi@linux.vnet.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/arch/microblaze/mm/highmem.c b/arch/microblaze/mm/highmem.c
index 5a92576fad92..2fcc5a52d84d 100644
--- a/arch/microblaze/mm/highmem.c
+++ b/arch/microblaze/mm/highmem.c
@@ -37,7 +37,7 @@ void *kmap_atomic_prot(struct page *page, pgprot_t prot)
         unsigned long vaddr;
         int idx, type;
 
-        /* even !CONFIG_PREEMPT needs this, for in_atomic in do_page_fault */
+        preempt_disable();
         pagefault_disable();
         if (!PageHighMem(page))
                 return page_address(page);
@@ -63,6 +63,7 @@ void __kunmap_atomic(void *kvaddr)
 
         if (vaddr < __fix_to_virt(FIX_KMAP_END)) {
                 pagefault_enable();
+                preempt_enable();
                 return;
         }
 
@@ -84,5 +85,6 @@ void __kunmap_atomic(void *kvaddr)
 #endif
         kmap_atomic_idx_pop();
         pagefault_enable();
+        preempt_enable();
 }
 EXPORT_SYMBOL(__kunmap_atomic);