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SubjectRe: [PATCH v2] coresight: core: Fix coresight device probe failure issue
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Hi Jinlong

On 04/03/2022 08:23, Mao Jinlong wrote:
> It is possibe that probe failure issue happens when the device
> and its child_device's probe happens at the same time.
> In coresight_make_links, has_conns_grp is true for parent, but
> has_conns_grp is false for child device as has_conns_grp is set
> to true in coresight_create_conns_sysfs_group. The probe of parent
> device will fail at this condition. Add has_conns_grp check for
> child device before make the links and make the process from
> device_register to connection_create be atomic to avoid this
> probe failure issue.
>
> Suggested-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> Suggested-by: Mike Leach <mike.leach@linaro.org>
> Signed-off-by: Mao Jinlong <quic_jinlmao@quicinc.com>
> ---
> drivers/hwtracing/coresight/coresight-core.c | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index 88653d1c06a4..b3e3bc59c09b 100644
> --- a/drivers/hwtracing/coresight/coresight-core.c
> +++ b/drivers/hwtracing/coresight/coresight-core.c
> @@ -1382,7 +1382,7 @@ static int coresight_fixup_device_conns(struct coresight_device *csdev)
> continue;
> conn->child_dev =
> coresight_find_csdev_by_fwnode(conn->child_fwnode);
> - if (conn->child_dev) {
> + if (conn->child_dev && conn->child_dev->has_conns_grp) {
> ret = coresight_make_links(csdev, conn,
> conn->child_dev);
> if (ret)
> @@ -1594,7 +1594,8 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
> refcnts = kcalloc(nr_refcnts, sizeof(*refcnts), GFP_KERNEL);
> if (!refcnts) {
> ret = -ENOMEM;
> - goto err_free_csdev;
> + kfree(csdev);
> + goto err_out;
> }
>
> csdev->refcnt = refcnts;
> @@ -1619,8 +1620,10 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
> csdev->dev.fwnode = fwnode_handle_get(dev_fwnode(desc->dev));
> dev_set_name(&csdev->dev, "%s", desc->name);
>
> + mutex_lock(&coresight_mutex);
> ret = device_register(&csdev->dev);
> if (ret) {
> + mutex_unlock(&coresight_mutex);
> put_device(&csdev->dev);
> /*
> * All resources are free'd explicitly via
> @@ -1634,6 +1637,7 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
> ret = etm_perf_add_symlink_sink(csdev);
>
> if (ret) {
> + mutex_unlock(&coresight_mutex);
> device_unregister(&csdev->dev);
> /*
> * As with the above, all resources are free'd
> @@ -1645,8 +1649,6 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
> }
> }
>
> - mutex_lock(&coresight_mutex);
> -
> ret = coresight_create_conns_sysfs_group(csdev);
> if (!ret)
> ret = coresight_fixup_device_conns(csdev);
> @@ -1663,8 +1665,6 @@ struct coresight_device *coresight_register(struct coresight_desc *desc)
>
> return csdev;
>
> -err_free_csdev:
> - kfree(csdev);
> err_out:
> /* Cleanup the connection information */
> coresight_release_platform_data(NULL, desc->pdata);

Could we consolidate the unlock sequence to a single point with
something like this (untested):


diff --git a/drivers/hwtracing/coresight/coresight-core.c
b/drivers/hwtracing/coresight/coresight-core.c
index af00dca8d1ac..198ee140c6e6 100644
--- a/drivers/hwtracing/coresight/coresight-core.c
+++ b/drivers/hwtracing/coresight/coresight-core.c
@@ -1571,6 +1571,7 @@ struct coresight_device *coresight_register(struct
coresight_desc *desc)
int nr_refcnts = 1;
atomic_t *refcnts = NULL;
struct coresight_device *csdev;
+ bool registered = false;

csdev = kzalloc(sizeof(*csdev), GFP_KERNEL);
if (!csdev) {
@@ -1591,7 +1592,8 @@ struct coresight_device *coresight_register(struct
coresight_desc *desc)
refcnts = kcalloc(nr_refcnts, sizeof(*refcnts), GFP_KERNEL);
if (!refcnts) {
ret = -ENOMEM;
- goto err_free_csdev;
+ kfree(csdev);
+ goto err_out;
}

csdev->refcnt = refcnts;
@@ -1616,6 +1618,13 @@ struct coresight_device
*coresight_register(struct coresight_desc *desc)
csdev->dev.fwnode = fwnode_handle_get(dev_fwnode(desc->dev));
dev_set_name(&csdev->dev, "%s", desc->name);

+ /*
+ * Make sure the device registration and the connection fixup
+ * are synchronised, so that we don't see uninitialised devices
+ * on the coresight bus while trying to resolve the connections.
+ */
+ mutex_lock(&coresight_mutex);
+
ret = device_register(&csdev->dev);
if (ret) {
put_device(&csdev->dev);
@@ -1623,7 +1632,7 @@ struct coresight_device *coresight_register(struct
coresight_desc *desc)
* All resources are free'd explicitly via
* coresight_device_release(), triggered from put_device().
*/
- goto err_out;
+ goto out_unlock;
}

if (csdev->type == CORESIGHT_DEV_TYPE_SINK ||
@@ -1638,11 +1647,11 @@ struct coresight_device
*coresight_register(struct coresight_desc *desc)
* from put_device(), which is in turn called from
* function device_unregister().
*/
- goto err_out;
+ goto out_unlock;
}
}
-
- mutex_lock(&coresight_mutex);
+ /* Device is now registered */
+ registered = true;

ret = coresight_create_conns_sysfs_group(csdev);
if (!ret)
@@ -1652,16 +1661,15 @@ struct coresight_device
*coresight_register(struct coresight_desc *desc)
if (!ret && cti_assoc_ops && cti_assoc_ops->add)
cti_assoc_ops->add(csdev);

+out_unlock:
mutex_unlock(&coresight_mutex);
- if (ret) {
+ /* Success */
+ if (!ret)
+ return csdev;
+
+ /* Unregister the device if needed */
+ if (registered)
coresight_unregister(csdev);
- return ERR_PTR(ret);
- }
-
- return csdev;
-
-err_free_csdev:
- kfree(csdev);
err_out:
/* Cleanup the connection information */
coresight_release_platform_data(NULL, desc->pdata);
--
2.35.1
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