percpu: fix pcpu_reclaim() locking

pcpu_reclaim() calls pcpu_depopulate_chunk() which makes use of pages
array and bitmap returned by pcpu_get_pages_and_bitmap() and thus
should be called under pcpu_alloc_mutex.  pcpu_reclaim() released the
mutex before calling depopulate leading to double free and other
strange problems caused by the unexpected concurrent usages of pages
array and bitmap.  Fix it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Christoph Lameter <cl@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/mm/percpu.c b/mm/percpu.c
index 3f9f182f9b44..42ab0024a6ed 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1181,12 +1181,13 @@ static void pcpu_reclaim(struct work_struct *work)
         }
 
         spin_unlock_irq(&pcpu_lock);
-        mutex_unlock(&pcpu_alloc_mutex);
 
         list_for_each_entry_safe(chunk, next, &todo, list) {
                 pcpu_depopulate_chunk(chunk, 0, pcpu_unit_size);
                 free_pcpu_chunk(chunk);
         }
+
+        mutex_unlock(&pcpu_alloc_mutex);
 }
 
 /**