From: Henry Burns henryburns@google.com Subject: mm/z3fold.c: fix z3fold_destroy_pool() ordering

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 ---

mm/z3fold.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)

--- a/mm/z3fold.c~mm-z3foldc-fix-z3fold_destroy_pool-ordering +++ a/mm/z3fold.c @@ -818,8 +818,15 @@ static void z3fold_destroy_pool(struct z { 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); }

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