Messages in this thread | | | Date | Tue, 1 Mar 2022 21:30:52 +0800 | Subject | Re: [PATCH] coresight: Defer probe when the child dev is not probed | From | Jinlong Mao <> |
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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, >> >> >
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