[PATCH v2 3/4] cxl/mem: Do not rely on device_add() side effects for dev_set_name() failures

Dan Williams
2021-03-30T02:48:54Z

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@nvidia.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.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;
}