linux-kernel - [PATCH v2 3/4] cxl/mem: Do not rely on device_add() side effects for dev_set

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Date:   Mon, 29 Mar 2021 19:47:55 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     linux-cxl@...r.kernel.org
Cc:     Jason Gunthorpe <jgg@...dia.com>, linux-kernel@...r.kernel.org,
        vishal.l.verma@...el.com, ira.weiny@...el.com,
        alison.schofield@...el.com
Subject: [PATCH v2 3/4] cxl/mem: Do not rely on device_add() side effects
 for dev_set_name() failures

While device_add() will happen to catch dev_set_name() failures it is a
broken pattern to follow given that the core may try to fall back to a
different name.

Add explicit checking for dev_set_name() failures to be cleaned up by
put_device(). Skip cdev_device_add() and proceed directly to
put_device() if the name set fails.

This type of bug is easier to see if 'alloc' is split from 'add'
operations that require put_device() on failure. So cxl_memdev_alloc()
is split out as a result.

Fixes: b39cb1052a5c ("cxl/mem: Register CXL memX devices")
Reported-by: Jason Gunthorpe <jgg@...dia.com>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 drivers/cxl/mem.c |   39 +++++++++++++++++++++++++++++----------
 1 file changed, 29 insertions(+), 10 deletions(-)

diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
index 548d696f1f54..508f0dc483f2 100644
--- a/drivers/cxl/mem.c
+++ b/drivers/cxl/mem.c
@@ -1181,7 +1181,7 @@ static void cxlmdev_unregister(void *_cxlmd)
 	put_device(dev);
 }
 
-static int cxl_mem_add_memdev(struct cxl_mem *cxlm)
+static struct cxl_memdev *cxl_memdev_alloc(struct cxl_mem *cxlm)
 {
 	struct pci_dev *pdev = cxlm->pdev;
 	struct cxl_memdev *cxlmd;
@@ -1191,7 +1191,7 @@ static int cxl_mem_add_memdev(struct cxl_mem *cxlm)
 
 	cxlmd = kzalloc(sizeof(*cxlmd), GFP_KERNEL);
 	if (!cxlmd)
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 
 	/*
 	 * @cxlm is released when the driver unbinds so srcu and
@@ -1201,7 +1201,7 @@ static int cxl_mem_add_memdev(struct cxl_mem *cxlm)
 
 	rc = ida_alloc_range(&cxl_memdev_ida, 0, CXL_MEM_MAX_DEVS, GFP_KERNEL);
 	if (rc < 0)
-		goto err_id;
+		goto err;
 	cxlmd->id = rc;
 
 	dev = &cxlmd->dev;
@@ -1210,27 +1210,46 @@ static int cxl_mem_add_memdev(struct cxl_mem *cxlm)
 	dev->bus = &cxl_bus_type;
 	dev->devt = MKDEV(cxl_mem_major, cxlmd->id);
 	dev->type = &cxl_memdev_type;
-	dev_set_name(dev, "mem%d", cxlmd->id);
 
 	cdev = &cxlmd->cdev;
 	cdev_init(cdev, &cxl_memdev_fops);
+	return cxlmd;
+
+err:
+	kfree(cxlmd);
+	return ERR_PTR(rc);
+}
+
+static int cxl_mem_add_memdev(struct cxl_mem *cxlm)
+{
+	struct cxl_memdev *cxlmd;
+	struct device *dev;
+	struct cdev *cdev;
+	int rc;
+
+	cxlmd = cxl_memdev_alloc(cxlm);
+	if (IS_ERR(cxlmd))
+		return PTR_ERR(cxlmd);
+
+	dev = &cxlmd->dev;
+	rc = dev_set_name(dev, "mem%d", cxlmd->id);
+	if (rc)
+		goto err;
 
+	cdev = &cxlmd->cdev;
 	rc = cdev_device_add(cdev, dev);
 	if (rc)
-		goto err_add;
+		goto err;
 
 	return devm_add_action_or_reset(dev->parent, cxlmdev_unregister, cxlmd);
 
-err_add:
+err:
 	/*
 	 * The cdev was briefly live, flush any ioctl operations that
 	 * saw that state.
 	 */
 	synchronize_srcu(&cxl_memdev_srcu);
-	ida_free(&cxl_memdev_ida, cxlmd->id);
-err_id:
-	kfree(cxlmd);
-
+	put_device(dev);
 	return rc;
 }