[snap] Allow chromium snap to access Pressure Stall Information (PSI)

[Haw Loeung]

Hi,

Currently seeing this:

| Mar 25 16:12:23 dharkan.local kernel: audit: type=1400 audit(1711343543.539:657): apparmor="DENIED" operation="open" class="file" profile="snap.chromium.chromium" name="/proc/pressure/cpu" pid=63335 comm="ThreadPoolForeg" requested_mask="r" denied_mask="r" fsuid=3134 ouid=0
| Mar 25 16:12:23 dharkan.local kernel: audit: type=1400 audit(1711343543.539:658): apparmor="DENIED" operation="open" class="file" profile="snap.chromium.chromium" name="/proc/pressure/io" pid=63335 comm="ThreadPoolForeg" requested_mask="r" denied_mask="r" fsuid=3134 ouid=0
| Mar 25 16:12:23 dharkan.local kernel: audit: type=1400 audit(1711343543.539:659): apparmor="DENIED" operation="open" class="file" profile="snap.chromium.chromium" name="/proc/pressure/memory" pid=63335 comm="ThreadPoolForeg" requested_mask="r" denied_mask="r" fsuid=3134 ouid>

It seems the AppAmor profile should be updated to allow Chromium access to the pressure stall information for it to monitor and manage it's processes?

[Nathan Teodosio (nteodosio)]

Hello, do you have a reproduction case? I don't get this when I launch
Chromium, does it try that when on heavy load?

[Haw Loeung (hloeung)]

Sorry, I should have mentioned the version. I'm using the chromium from the candidate channel:

| $ snap info chromium | grep installed
| installed: 123.0.6312.58 (2795) 168MB -

Seems to be happening every 10 mins.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Haw Loeung (hloeung)]

It's used here:

| https://github.com/chromium/chromium/blob/123.0.6312.58/chrome/browser/metrics/pressure/pressure_metrics_reporter.cc#L19

From this commit:

| https://github.com/chromium/chromium/commit/dace5562b1d56bf2d2e5b2de6f4518c44844be9f

References this bug:

| https://issues.chromium.org/issues/40256157

[Nathan Teodosio (nteodosio)]

I reproduced that now.

Do you observe any problem or hindrance as a result of those denials?

I had a look at the source code and it seems that it doesn't actually
use that information for load balancing or anything of the sorts, but
actually only for informational purposes, namely for assembling
histograms and reporting the results to the so called UMA, User Metrics
Analysis according to the developer's glossary, for instance if the user
chooses to report a session crash back to Google.

[Haw Loeung (hloeung)]

I've not observed any problems or hindrance as a result of these denials, no.

Just more noise and thought maybe Chromium was going to use the pressure stall information for something useful like for the selection of which tabs/process to kill off when the system is experiencing pressure in either CPU, I/O, and/or memory.

But all good if it does not and it does not plan to.

[Kamal Mostafa (kamalmostafa)]

Spamming three lines to dmesg every 10 minutes forever is pretty intolerable. Please fix this regression.