RFR: 8286212: Cgroup v1 initialization causes NPE on some systems [v3]

[Severin Gehwolf]

On Thu, 19 May 2022 06:00:06 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> Severin Gehwolf has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Refactor hotspot gtest
>>  - Separate into function. Fix comment.
>
> src/hotspot/os/linux/cgroupV1Subsystem_linux.cpp line 86:
> 
>> 84:           const char* cgroup_p = cgroup_path;
>> 85:           int last_slash = find_last_slash_pos(root_p, cgroup_p);
>> 86:           assert(last_slash >= 0, "not an absolute path?");
> 
> Are root_p and cgroup_p directly read from the /proc/xxx files. If so, do we validate the input to make sure they are absolute paths?
> 
> It seems like our code cannot handle trailing '/' in the input. If so, we should clear all trailing '/' from the input string. Then, in functions that process them, we should assert that they don't end with slash. See my comment in find_last_slash_pos().

Yes, those values come from `/proc/self/mountinfo` and `/proc/self/cgroup`. There is no validation being done. Then again, we only end up in this branch if the root path is not a substring of the cgroup path. In that case trailing slashes don't matter, since there would not be a character by character match earlier.

I'll add handling of trailing slashes and appropriate asserts where it makes sense.

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PR: https://git.openjdk.java.net/jdk/pull/8629