linux-kernel - Re: [PATCH 3/3] tools/lib/fs: Cache cgroupfs mount point

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 21 Jan 2021 13:33:37 +0900
From:   Namhyung Kim <namhyung@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Ian Rogers <irogers@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 3/3] tools/lib/fs: Cache cgroupfs mount point

Hi Arnaldo,

Can you share your thoughts on this?

On Fri, Jan 8, 2021 at 2:51 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> On Wed, Jan 6, 2021 at 10:33 AM Namhyung Kim <namhyung@...nel.org> wrote:
> >
> > Hi Arnaldo,
> >
> > On Tue, Dec 29, 2020 at 8:51 PM Arnaldo Carvalho de Melo
> > <acme@...nel.org> wrote:
> > >
> > > Em Wed, Dec 16, 2020 at 06:05:56PM +0900, Namhyung Kim escreveu:
> > > > Currently it parses the /proc file everytime it opens a file in the
> > > > cgroupfs.  Save the last result to avoid it (assuming it won't be
> > > > changed between the accesses).
> > >
> > > Which is the most likely case, but can't we use something like inotify
> > > to detect that and bail out or warn the user?
> >
> > Hmm.. looks doable.  Will check.
>
> So I've played with inotify a little bit, and it seems it needs to monitor
> changes on the file or the directory.  I didn't get any notification from
> the /proc/mounts file even if I did some mount/umount.
>
> Instead, I could get IN_UNMOUNT when the cgroup filesystem was
> unmounted.  But for the monitoring, we need to do one of a) select-like
> syscall to wait for the events, b) signal-driven IO notification or c) read
> the inotify file with non-block mode everytime.
>
> In a library code, I don't think we can do a) or b) since it can affect
> user program behaviors.  Then we should go with c) but I think
> it's opposite to the purpose of this patch. :)
>
> As you said, I think mostly we don't care as the accesses will happen
> in a short period of time.  But if you really care, maybe for the upcoming
> perf daemon changes, I think we can add an API to invalidate the cache
> or internal time-based invalidation logic (like remove it after 10 sec.).
>
> Thoughts?
>
> Thanks,
> Namhyung