linux-kernel - [PATCH 2/4] cxl/mem: Fix cdev_device

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Date:   Wed, 24 Mar 2021 14:01:56 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     linux-cxl@...r.kernel.org
Cc:     Jason Gunthorpe <jgg@...dia.com>, ira.weiny@...el.com,
        vishal.l.verma@...el.com, alison.schofield@...el.com,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/4] cxl/mem: Fix cdev_device_add() error handling

If cdev_device_add() fails then the allocation performed by
dev_set_name() is leaked. Use put_device(), not open coded release, for
device_add() failures.

The comment is obsolete because direct err_id failures need not worry
about the device being live.

The release method expects the percpu_ref is already dead, so
percpu_ref_kill() is needed before put_device(). However, given that the
cdev was partially live wait_for_completion() also belongs in the
release method.

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 |   16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
index 30bf4f0f3c17..e53d573ae4ab 100644
--- a/drivers/cxl/mem.c
+++ b/drivers/cxl/mem.c
@@ -1049,6 +1049,7 @@ static void cxl_memdev_release(struct device *dev)
 {
 	struct cxl_memdev *cxlmd = to_cxl_memdev(dev);
 
+	wait_for_completion(&cxlmd->ops_dead);
 	percpu_ref_exit(&cxlmd->ops_active);
 	ida_free(&cxl_memdev_ida, cxlmd->id);
 	kfree(cxlmd);
@@ -1157,7 +1158,6 @@ static void cxlmdev_unregister(void *_cxlmd)
 
 	percpu_ref_kill(&cxlmd->ops_active);
 	cdev_device_del(&cxlmd->cdev, dev);
-	wait_for_completion(&cxlmd->ops_dead);
 	cxlmd->cxlm = NULL;
 	put_device(dev);
 }
@@ -1210,20 +1210,16 @@ static int cxl_mem_add_memdev(struct cxl_mem *cxlm)
 	cdev_init(cdev, &cxl_memdev_fops);
 
 	rc = cdev_device_add(cdev, dev);
-	if (rc)
-		goto err_add;
+	if (rc) {
+		percpu_ref_kill(&cxlmd->ops_active);
+		put_device(dev);
+		return rc;
+	}
 
 	return devm_add_action_or_reset(dev->parent, cxlmdev_unregister, cxlmd);
 
-err_add:
-	ida_free(&cxl_memdev_ida, cxlmd->id);
 err_id:
-	/*
-	 * Theoretically userspace could have already entered the fops,
-	 * so flush ops_active.
-	 */
 	percpu_ref_kill(&cxlmd->ops_active);
-	wait_for_completion(&cxlmd->ops_dead);
 	percpu_ref_exit(&cxlmd->ops_active);
 err_ref:
 	kfree(cxlmd);