Hi Benjamin,
On Wed, Jan 08, 2020 at 09:24:30AM +0900, Benjamin Poirier wrote:
[...]
> Looks like the modules are built before lttng-sessiond is started:
> Setting up lttng-modules-dkms (2.11.0-2) ...
> Loading new lttng-modules-2.11.0 DKMS files...
> Building for 5.4.0-2-amd64
> Building initial module for 5.4.0-2-amd64
> Done.
>
> lttng-lib-ring-buffer.ko:
> Running module version sanity check.
> - Original module
> - No original module exists within this kernel
> - Installation
> - Installing to /lib/modules/5.4.0-2-amd64/updates/dkms/
>
> [...]
>
> depmod...
>
> DKMS: install completed.
> Setting up linux-headers-5.4.0-2-amd64 (5.4.8-1) ...
> /etc/kernel/header_postinst.d/dkms:
> dkms: running auto installation service for kernel 5.4.0-2-amd64:.
> Setting up sudo (1.8.29-1) ...
> Setting up babeltrace (1.5.7-2) ...
> Setting up liburcu6:amd64 (0.11.1-2) ...
> Setting up linux-headers-amd64 (5.4.8-1) ...
> Setting up liblttng-ctl0:amd64 (2.11.0-3) ...
> Setting up lttng-tools (2.11.0-3) ...
>
> Still, it doesn't work.
>
> > Simply restarting the sessiond should fix this.
>
> I tried restarting lttng-sessiond or rebooting the machine but it was no
> help, lttng-sessiond always reports:
> Error: Failed to load kmod library resources
> Warning: No kernel tracer available
>
> A quick look into the code shows that is:
> src/bin/lttng-sessiond/modprobe.c
> kmod_set_log_fn(*ctx, log_kmod, NULL);
> ret = kmod_load_resources(*ctx);
> if (ret < 0) {
> ERR("Failed to load kmod library resources");
> goto error;
> }
>
> I didn't dig into libkmod, but I noticed (using opensnoop.bt) the
> following:
> 8071 lttng-sessiond 2 0
> /lib/modules/5.4.0-2-amd64/modules.dep.bin
> 8071 lttng-sessiond 2 0
> /lib/modules/5.4.0-2-amd64/modules.alias.bin
> 8071 lttng-sessiond 2 0
> /lib/modules/5.4.0-2-amd64/modules.symbols.bin
> 8071 lttng-sessiond 2 0
> /lib/modules/5.4.0-2-amd64/modules.builtin.alias.bin
>
> On another machine which I haven't yet updated and where lttng still
> works, I see:
> 193519 lttng-sessiond 2 0
> /lib/modules/5.4.0-1-amd64/modules.dep.bin
> 193519 lttng-sessiond 2 0
> /lib/modules/5.4.0-1-amd64/modules.alias.bin
> 193519 lttng-sessiond 2 0
> /lib/modules/5.4.0-1-amd64/modules.symbols.bin
> 193519 lttng-sessiond 2 0
> /lib/modules/5.4.0-1-amd64/modules.builtin.bin
>
> Not sure if /lib/modules/5.4.0-2-amd64/modules.builtin.alias.bin is
> relevant but it's an empty file...
>
> After downgrading libkmod2 from
> Version: 26+20191223-1
> to
> Version: 26-3
> the issue with lttng is no longer apparent:
> root@vsid:/tmp# lttng list --kernel
> Kernel events:
> -------------
> asoc_snd_soc_bias_level_start (loglevel: TRACE_EMERG (0)) (type:
> tracepoint)
> asoc_snd_soc_bias_level_done (loglevel: TRACE_EMERG (0)) (type:
> tracepoint)
> asoc_snd_soc_dapm_start (loglevel: TRACE_EMERG (0)) (type:
> tracepoint)
> [...]
>
Should we track this in a separate bug from #948257?
Regards,
Salvatore
