linux-kernel - Re: [PATCH 12/22] perf daemon: Allow only one daemon over base directory

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Date:   Tue, 19 Jan 2021 18:44:32 +0100
From:   Jiri Olsa <jolsa@...hat.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Petlan <mpetlan@...hat.com>,
        Ian Rogers <irogers@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        Alexei Budankov <abudankov@...wei.com>
Subject: Re: [PATCH 12/22] perf daemon: Allow only one daemon over base
 directory

On Tue, Jan 19, 2021 at 02:37:42PM +0900, Namhyung Kim wrote:

SNIP

> >
> > +static int check_lock(struct daemon *daemon)
> > +{
> > +       char path[PATH_MAX];
> > +       char buf[20];
> > +       int fd, pid;
> > +       ssize_t len;
> > +
> > +       scnprintf(path, sizeof(path), "%s/lock", daemon->base);
> > +
> > +       fd = open(path, O_RDWR|O_CREAT|O_CLOEXEC, 0640);
> > +       if (fd < 0)
> > +               return -1;
> > +
> > +       if (lockf(fd, F_TLOCK, 0) < 0) {
> > +               filename__read_int(path, &pid);
> > +               fprintf(stderr, "failed: another perf daemon (pid %d) owns %s\n",
> > +                       pid, daemon->base);
> > +               return -1;
> > +       }
> 
> So the fd is (a kind of) leaked and the lock is released only when
> the daemon is going to die, right?

yes, that's the idea, I'll put it in some comment

thanks,
jirka