Hi
On 01/03/2022 13:30, Jinlong Mao wrote:
Hi Mike,
On 3/1/2022 9:15 PM, Mike Leach wrote:
Hi,
On Tue, 1 Mar 2022 at 11:42, Jinlong Mao <quic_jinlmao@xxxxxxxxxxx>
wrote:
On 2/28/2022 10:51 PM, Suzuki K Poulose wrote:
...
Hi Suzuki,
This issue happens when race condition happens.
The condition is that the device and its child_device's probe happens
at the same time.
For example: device0 and its child device device1.
Both of them are calling coresight_register function. device0 is
calling coresight_fixup_device_conns.
device1 is waiting for device0 to release the coresight_mutex.
Because device1's csdev node is allocated,
coresight_make_links will be called for device0. Then in
coresight_add_sysfs_link, has_conns_grp is true
for device0, but has_conns_grp is false for device1 as has_conns_grp
is set to true in coresight_create_conns_sysfs_group .
The probe of device0 will fail for at this condition.
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);
if (!ret)
ret = coresight_fixup_orphan_conns(csdev);
if (!ret && cti_assoc_ops && cti_assoc_ops->add)
cti_assoc_ops->add(csdev);
mutex_unlock(&coresight_mutex);
.........
}
static int coresight_fixup_device_conns(struct coresight_device *csdev)
{
..........
conn->child_dev =
coresight_find_csdev_by_fwnode(conn->child_fwnode);
The issue appears to be a constraint hidden in the lower layers of the
code.
Would a better solution not be to alter the code here:
if (conn->child_dev && conn->child_dev->has_conns_grp) {
...
} else {
csdev->orphan = true;
}
which would mean that the connection attempt would drop through to
label the connection as an orphan, to be cleaned up by the child
itself when it runs coresight_fixup_orphan_conns()
Tnanks Mike, I think that is a good solution. Alternatively, we
could make sure that device_register() and the fixup following
that are atomic.
i.e.
mutex_lock()
device_register()
fixup_connections()
create_sysfs()
mutex_unlock();
The fix may be a bit invasive than Mike's proposal, but it makes
sure we don't end up with half baked device on the coresight-bus.
Suzuki
