Commit 6051d3bd authored by Henry Burns's avatar Henry Burns Committed by Linus Torvalds

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: 5d03a661 ("mm/z3fold.c: use kref to prevent page free/compact race")
Signed-off-by: default avatarHenry Burns <henryburns@google.com>
Reviewed-by: default avatarShakeel Butt <shakeelb@google.com>
Reviewed-by: default avatarJonathan 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent a53190a4
......@@ -818,8 +818,15 @@ 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);
}
......
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