Bug #873

Unable to Trace Event on OutOfTree Kernel Module on Centos7.

Added by Damien COTTIER almost 6 years ago.

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Hi all,
I wish you first a happy new year.

I submit this bug on lttng-modules, but i know that the issue is more a generic kernel tracing issue on
3.10.0-123 kernel used on Centos7.

Unfortunately we decide to move our system for Fedora17 to Centos7, but all the tracepoints we defined in our
pcie drivers (not yet committed into vanilla tree) is no more usable in Centos7.

I saw the various patches Mathieu propose to fix the issue:
45ab2813d40d88fc575e753c38478de242d03f88 available in 3.10.34 (d6a6d1f38ce55aa5a7d8aab972176660b19fd7ab)
and finally
66cc69e34e86a231fbe68d8918c6119e3b7549a3 and 57673c2b0baa900dddae3b9eb3d7748ebf550eb3 available in mainline 3.15 and never back ported to 3.10.

However even in last linux-3.10.0-123.13.2.el7 from rhel7, the first patch available in 3.10.34 is not integrated, leading
in existing but not functional sysfs trace event entries.

If i understood well, the only way to get proper initialisation of trace events is either to:
- Rebuild the kernel disabling the CONFIG_MODULE_SIG or try some internal patches and deliver it to our customer (we would prefer avoid such solution)
- Signing our OOT modules (i don't know exactly how to proceed, my trials with manual procedure fails,
probably because our key was not signed by Centos key)
- Ask for Redhat to introduce all above pathes in 3.10 (expect no miracle from this side)

Moreover we are using dkms to create kernel module packages to deliver to our customer, I read somewhere that dkms does not
support signing mechanism.

we also used to deliver all lttng framework (tools, ust, kernel module...) in our own packages (fc17 doesn't provide lttng in their default repository),
leading in centos7 to have all lttng modules in addition to ours with taint flags (OF).

Do you have any idea on how to proceed to workaround this issue and
being able to trace our driver on centos7?

Thanks and regards.

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