The patch titled Subject: mm/z3fold.c: fix z3fold_destroy_pool() ordering has been added to the -mm tree. Its filename is mm-z3foldc-fix-z3fold_destroy_pool-ordering.patch

This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-z3foldc-fix-z3fold_destroy_pool-... and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-z3foldc-fix-z3fold_destroy_pool-...

Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next and is updated there every 3-4 working days

------------------------------------------------------ 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 Cc: Vitaly Vul vitaly.vul@sony.com Cc: Vitaly Wool vitalywool@gmail.com Cc: Jonathan Adams jwadams@google.com Cc: David Howells dhowells@redhat.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Al Viro <viro@zeniv.linux.org.uk 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); }

_

Patches currently in -mm which might be from henryburns@google.com are

mm-z3foldc-fix-z3fold_destroy_pool-ordering.patch mm-z3foldc-fix-z3fold_destroy_pool-race-condition.patch