Re: [PATCH] coresight: Defer probe when the child dev is not probed

[Jinlong Mao <quic_jinlmao@quicinc.com>]

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@quicinc.com> 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@qti.qualcomm.com>
>>
>> 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@qti.qualcomm.com>
>> ---
>>    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,
>>
>>
>