linux-kernel - [PATCH 4.18 085/158] device-dax: avoid hang on error before devm_memremap

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Message-Id: <20180917211715.132439137@linuxfoundation.org>
Date:   Tue, 18 Sep 2018 00:41:55 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Stefan Hajnoczi <stefanha@...hat.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Sasha Levin <alexander.levin@...rosoft.com>
Subject: [PATCH 4.18 085/158] device-dax: avoid hang on error before devm_memremap_pages()

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stefan Hajnoczi <stefanha@...hat.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 = devm_add_action_or_reset(dev, dax_pmem_percpu_exit,
  				&dax_pmem->ref);
  if (rc)
  	return rc;

  dax_pmem->pgmap.ref = &dax_pmem->ref;
  addr = 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@...hat.com>
Signed-off-by: Dave Jiang <dave.jiang@...el.com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/dax/pmem.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

--- a/drivers/dax/pmem.c
+++ b/drivers/dax/pmem.c
@@ -105,15 +105,19 @@ static int dax_pmem_probe(struct device
 	if (rc)
 		return rc;
 
-	rc = devm_add_action_or_reset(dev, dax_pmem_percpu_exit,
-							&dax_pmem->ref);
-	if (rc)
+	rc = devm_add_action(dev, dax_pmem_percpu_exit, &dax_pmem->ref);
+	if (rc) {
+		percpu_ref_exit(&dax_pmem->ref);
 		return rc;
+	}
 
 	dax_pmem->pgmap.ref = &dax_pmem->ref;
 	addr = 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);
+	}
 
 	rc = devm_add_action_or_reset(dev, dax_pmem_percpu_kill,
 							&dax_pmem->ref);