[PATCH v3] cxl/memdev: fix deadlock in cxl_memdev_autoremove() on attach failure

[Gregory Price]

cxl_memdev_autoremove() takes device_lock(&cxlmd->dev) via guard(device)
and then calls cxl_memdev_unregister() when the attach callback was
provided but cxl_mem_probe() failed to bind.

cxl_memdev_unregister() calls
  cdev_device_del()
    device_del()
      bus_remove_device()
        device_release_driver()

This path is reached when a driver uses the @attach parameter to
devm_cxl_add_memdev() and the CXL topology fails to enumerate (e.g.
DVSEC range registers decode outside platform-defined CXL ranges,
causing the endpoint port probe to fail).

Add cxl_memdev_attach_failed() to set the scope of the check correctly.

Fixes: 29317f8dc6ed ("cxl/mem: Introduce cxl_memdev_attach for CXL-dependent operation")
Signed-off-by: Gregory Price <gourry@xxxxxxxxxx>
---
 drivers/cxl/core/memdev.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
index af3d0cc65138..25ca4443e4f7 100644
--- a/drivers/cxl/core/memdev.c
+++ b/drivers/cxl/core/memdev.c
@@ -1089,10 +1089,8 @@ static int cxlmd_add(struct cxl_memdev *cxlmd, struct cxl_dev_state *cxlds)
 DEFINE_FREE(put_cxlmd, struct cxl_memdev *,
 	    if (!IS_ERR_OR_NULL(_T)) put_device(&_T->dev))
 
-static struct cxl_memdev *cxl_memdev_autoremove(struct cxl_memdev *cxlmd)
+static bool cxl_memdev_attach_failed(struct cxl_memdev *cxlmd)
 {
-	int rc;
-
 	/*
 	 * If @attach is provided fail if the driver is not attached upon
 	 * return. Note that failure here could be the result of a race to
@@ -1100,7 +1098,14 @@ static struct cxl_memdev *cxl_memdev_autoremove(struct cxl_memdev *cxlmd)
 	 * succeeded and then cxl_mem unbound before the lock is acquired.
 	 */
 	guard(device)(&cxlmd->dev);
-	if (cxlmd->attach && !cxlmd->dev.driver) {
+	return (cxlmd->attach && !cxlmd->dev.driver);
+}
+
+static struct cxl_memdev *cxl_memdev_autoremove(struct cxl_memdev *cxlmd)
+{
+	int rc;
+
+	if (cxl_memdev_attach_failed(cxlmd)) {
 		cxl_memdev_unregister(cxlmd);
 		return ERR_PTR(-ENXIO);
 	}
-- 
2.53.0