From: Henry Burns <henryburns@xxxxxxxxxx> Subject: mm/z3fold.c: fix z3fold_destroy_pool() race condition 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. Calling z3fold_deregister_migration() before the workqueues are drained means that there can be allocated pages referencing a freed inode, causing any thread in compaction to be able to trip over the bad pointer in PageMovable(). Link: http://lkml.kernel.org/r/20190726224810.79660-2-henryburns@xxxxxxxxxx Fixes: 1f862989b04a ("mm/z3fold.c: support page migration") 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 | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/mm/z3fold.c~mm-z3foldc-fix-z3fold_destroy_pool-race-condition +++ a/mm/z3fold.c @@ -817,16 +817,19 @@ out: static void z3fold_destroy_pool(struct z3fold_pool *pool) { kmem_cache_destroy(pool->c_handle); - z3fold_unregister_migration(pool); /* * 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). + * + * There are still outstanding pages until both workqueues are drained, + * so we cannot unregister migration until then. */ destroy_workqueue(pool->compact_wq); destroy_workqueue(pool->release_wq); + z3fold_unregister_migration(pool); kfree(pool); } _
