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Re: [dm-devel] [PATCH] dm-snapshot: workaround for a lockdep warning



Dne 18.9.2013 17:57, Mikulas Patocka napsal(a):


On Wed, 18 Sep 2013, Zdenek Kabelac wrote:

Dne 18.9.2013 02:08, Mikulas Patocka napsal(a):


On Tue, 17 Sep 2013, Mikulas Patocka wrote:

BTW. this patch is no longer needed on 3.11 because md->io_lock was
removed there, so the false lockdep warning doesn't happen.

So we need to get this patch to stable trees 3.5 to 3.10, but not
upstream. How to push the patch there without pushing it upstream?

Mikulas

It's more complicated than that - the original Zdenek's report shows that
the false warning happened on kernel "3.11.1-300.fc20.x86_64+debug". But I
am not able to reproduce the bug on 3.11, I only reproduced it on 3.5-3.10
kernels.

Zdenek, could you reproduce the bug on kernel 3.11?

Mikulas



Since I do not have clean 3.11 at my hands  - I've reproduced it with my -rc6
kernel (few patches based on 8495e9c4a9616c9d19f23182d0536485902259db)
With enabled kmemleak=on lockdep.prove_locking=1 lockdep.lock_stat=1.

So - try this patch and tell me if it fixes the problem:

Index: linux-2.6-devel/drivers/md/dm-snap-persistent.c
===================================================================
--- linux-2.6-devel.orig/drivers/md/dm-snap-persistent.c	2013-05-10 18:27:31.132358000 +0200
+++ linux-2.6-devel/drivers/md/dm-snap-persistent.c	2013-09-17 18:41:39.023940000 +0200
@@ -256,7 +256,7 @@
  	 */
  	INIT_WORK_ONSTACK(&req.work, do_metadata);
  	queue_work(ps->metadata_wq, &req.work);
-	flush_work(&req.work);
+	flush_workqueue(ps->metadata_wq);

  	return req.result;
  }


Yes - this seems to eliminate reported INFO.

Though I'm getting curious why some tests are running much much much slower when kmemleak and lockdep is in use.

Zdenek



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