From: Henry Burns <henryburns@xxxxxxxxxx>
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@xxxxxxxxxx
Fixes: 5d03a6613957 ("mm/z3fold.c: use kref to prevent page free/compact race")
Signed-off-by: Henry Burns <henryburns@xxxxxxxxxx>
Reviewed-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
Reviewed-by: Jonathan Adams <jwadams@xxxxxxxxxx>
Cc: Vitaly Vul <vitaly.vul@xxxxxxxx>
Cc: Vitaly Wool <vitalywool@xxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx
Cc: Henry Burns <henrywolfeburns@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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);
}
_
