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From:   Sasha Levin <Alexander.Levin@microsoft.com>
To:     "stable@vger.kernel.org" <stable@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
CC:     Stefan Hajnoczi <stefanha@redhat.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Sasha Levin <Alexander.Levin@microsoft.com>
Subject: [PATCH AUTOSEL 4.18 045/131] device-dax: avoid hang on error before
 devm_memremap_pages()
Thread-Topic: [PATCH AUTOSEL 4.18 045/131] device-dax: avoid hang on error
 before devm_memremap_pages()
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Date:   Sun, 2 Sep 2018 13:03:57 +0000
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From: Stefan Hajnoczi <stefanha@redhat.com>

[ Upstream commit b7751410c180a05fdc21268f8661b1480169b0df ]

dax_pmem_percpu_exit() waits for dax_pmem_percpu_release() to invoke the
dax_pmem->cmp completion.  Unfortunately this approach to cleaning up
the percpu_ref only works after devm_memremap_pages() was successful.

If devm_add_action_or_reset() or devm_memremap_pages() fails,
dax_pmem_percpu_release() is not invoked.  Therefore
dax_pmem_percpu_exit() hangs waiting for the completion:

  rc =3D devm_add_action_or_reset(dev, dax_pmem_percpu_exit,
  				&dax_pmem->ref);
  if (rc)
  	return rc;

  dax_pmem->pgmap.ref =3D &dax_pmem->ref;
  addr =3D devm_memremap_pages(dev, &dax_pmem->pgmap);

Avoid the hang by calling percpu_ref_exit() in the error paths instead
of going through dax_pmem_percpu_exit().

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
---
 drivers/dax/pmem.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/dax/pmem.c b/drivers/dax/pmem.c
index fd49b24fd6af..99e2aace8078 100644
--- a/drivers/dax/pmem.c
+++ b/drivers/dax/pmem.c
@@ -105,15 +105,19 @@ static int dax_pmem_probe(struct device *dev)
 	if (rc)
 		return rc;
=20
-	rc =3D devm_add_action_or_reset(dev, dax_pmem_percpu_exit,
-							&dax_pmem->ref);
-	if (rc)
+	rc =3D devm_add_action(dev, dax_pmem_percpu_exit, &dax_pmem->ref);
+	if (rc) {
+		percpu_ref_exit(&dax_pmem->ref);
 		return rc;
+	}
=20
 	dax_pmem->pgmap.ref =3D &dax_pmem->ref;
 	addr =3D devm_memremap_pages(dev, &dax_pmem->pgmap);
-	if (IS_ERR(addr))
+	if (IS_ERR(addr)) {
+		devm_remove_action(dev, dax_pmem_percpu_exit, &dax_pmem->ref);
+		percpu_ref_exit(&dax_pmem->ref);
 		return PTR_ERR(addr);
+	}
=20
 	rc =3D devm_add_action_or_reset(dev, dax_pmem_percpu_kill,
 							&dax_pmem->ref);
--=20
2.17.1