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

[Jinlong Mao]

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,