mm/z3fold.c: fix z3fold_destroy_pool() ordering

commit 6051d3bd3b91e96c59e62b8be2dba1cc2b19ee40 upstream.

The constraint from the zpool use of z3fold_destroy_pool() is there are
no outstanding handles to memory (so no active allocations), but it is
possible for there to be outstanding work on either of the two wqs in
the pool.

If there is work queued on pool->compact_workqueue when it is called,
z3fold_destroy_pool() will do:

   z3fold_destroy_pool()
     destroy_workqueue(pool->release_wq)
     destroy_workqueue(pool->compact_wq)
       drain_workqueue(pool->compact_wq)
         do_compact_page(zhdr)
           kref_put(&zhdr->refcount)
             __release_z3fold_page(zhdr, ...)
               queue_work_on(pool->release_wq, &pool->work) *BOOM*

So compact_wq needs to be destroyed before release_wq.

Link: http://lkml.kernel.org/r/20190726224810.79660-1-henryburns@google.com
Fixes: 5d03a6613957 ("mm/z3fold.c: use kref to prevent page free/compact race")
Signed-off-by: Henry Burns <henryburns@google.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Reviewed-by: Jonathan Adams <jwadams@google.com>
Cc: Vitaly Vul <vitaly.vul@sony.com>
Cc: Vitaly Wool <vitalywool@gmail.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Al Viro <viro@zeniv.linux.org.uk
Cc: Henry Burns <henrywolfeburns@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 3b27094dc42e1705e50813b4584d6d096db8c34b..d06d7f95600285e9a273a4fa474aa6f93a92e2ae 100644 (file)
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -820,8 +820,15 @@ static void z3fold_destroy_pool(struct z3fold_pool *pool)
 {
        kmem_cache_destroy(pool->c_handle);
        z3fold_unregister_migration(pool);
-       destroy_workqueue(pool->release_wq);
+
+       /*
+        * We need to destroy pool->compact_wq before pool->release_wq,
+        * as any pending work on pool->compact_wq will call
+        * queue_work(pool->release_wq, &pool->work).
+        */
+
        destroy_workqueue(pool->compact_wq);
+       destroy_workqueue(pool->release_wq);
        kfree(pool);
 }