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 Jinlong
On 28/02/2022 13:31, Mao Jinlong wrote:
From: Mao Jinlong <jinlmao@xxxxxxxxxxxxxxxx>
It is possible that when device probe, its child device is not
probed. Then it will fail when add sysfs connection for the device.
Make device defer probe when the child device is not probed.
Please could you a bit a more specific on the exact issue ?
I don't see a problem with probe deferral right now, with
coresight/next.
For e.g.,
root@juno-server:~# lsmod
Module Size Used by
coresight 73728 0
root@juno-server:~# ls /sys/bus/coresight/devices/
root@juno-server:~# modprobe coresight-etm4x
root@juno-server:~# lsmod
Module Size Used by
coresight_etm4x 81920 0
coresight 73728 1 coresight_etm4x
root@juno-server:~# ls /sys/bus/coresight/devices/
etm0 etm1
-- Note etm2-etm5 doesn't appear --
root@juno-server:~# modprobe coresight-funnel
root@juno-server:~# lsmod
Module Size Used by
coresight_funnel 20480 0
coresight_etm4x 81920 0
coresight 73728 2 coresight_etm4x,coresight_funnel
root@juno-server:~# ls /sys/bus/coresight/devices/
etm0 etm1
-- Still don't appear ---
root@juno-server:~# modprobe coresight-replicator
root@juno-server:~# ls /sys/bus/coresight/devices/
etm0 etm1
root@juno-server:~# modprobe coresight-tmc
-- At this stage, the devices automatically get probed and appear --
root@juno-server:~# ls /sys/bus/coresight/devices/
etm0 etm1 etm2 etm3 etm4 etm5 funnel0 funnel1 funnel2 tmc_etf0 tmc_etr0
root@juno-server:~# lsmod
Module Size Used by
coresight_tmc 40960 0
coresight_replicator 20480 0
coresight_funnel 20480 0
coresight_etm4x 81920 0
coresight 73728 4 coresight_tmc,coresight_etm4x,coresight_replicator,coresight_funnel
So, my question is, what is this patch trying to solve ?
Cheers
Suzuki
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()
Regards
Mike
Thanks Mike.
Your recommended fix looks much better than my fix. Let me try with it
and get back to you.
Thanks
Jinlong Mao
if (conn->child_dev) {
ret = coresight_make_links(csdev, conn,
conn->child_dev);
..........
}
int coresight_add_sysfs_link(struct coresight_sysfs_link *info)
{
................
if (!info->orig->has_conns_grp || !info->target->has_conns_grp)
return -EINVAL;
The probe fail issue is reproduced with reboot stress test on our internal device.
With the patch, the probe fail issue is not reproduced.
Thanks
Jinlong Mao
Signed-off-by: Mao Jinlong <jinlmao@xxxxxxxxxxxxxxxx>
---
drivers/hwtracing/coresight/coresight-sysfs.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/hwtracing/coresight/coresight-sysfs.c b/drivers/hwtracing/coresight/coresight-sysfs.c
index 34d2a2d31d00..7df9eb59bf2c 100644
--- a/drivers/hwtracing/coresight/coresight-sysfs.c
+++ b/drivers/hwtracing/coresight/coresight-sysfs.c
@@ -73,8 +73,10 @@ int coresight_add_sysfs_link(struct coresight_sysfs_link *info)
if (!info->orig || !info->target ||
!info->orig_name || !info->target_name)
return -EINVAL;
- if (!info->orig->has_conns_grp || !info->target->has_conns_grp)
+ if (!info->orig->has_conns_grp)
return -EINVAL;
+ if (!info->target->has_conns_grp)
+ return -EPROBE_DEFER;
/* first link orig->target */
ret = sysfs_add_link_to_group(&info->orig->dev.kobj,
