linux-kernel - Re: [for-next][PATCH 10/31] scripts: ftrace - move the sort-processing in ftrace

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Date:   Sat, 15 Jan 2022 22:59:20 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Yinan Liu <yinan@...ux.alibaba.com>, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kernel test robot <lkp@...el.com>,
        kernel test robot <oliver.sang@...el.com>,
        llvm@...ts.linux.dev
Subject: Re: [for-next][PATCH 10/31] scripts: ftrace - move the
 sort-processing in ftrace_init

On Sat, 15 Jan 2022 13:36:04 -0700
Nathan Chancellor <nathan@...nel.org> wrote:

> Hi Steven and Yinan,
> 
> On Tue, Jan 11, 2022 at 12:30:41PM -0500, Steven Rostedt wrote:
> > From: Yinan Liu <yinan@...ux.alibaba.com>
> > 
> > When the kernel starts, the initialization of ftrace takes
> > up a portion of the time (approximately 6~8ms) to sort mcount
> > addresses. We can save this time by moving mcount-sorting to
> > compile time.
> > 
> > Link: https://lkml.kernel.org/r/20211212113358.34208-2-yinan@linux.alibaba.com
> > 
> > Signed-off-by: Yinan Liu <yinan@...ux.alibaba.com>
> > Reported-by: kernel test robot <lkp@...el.com>
> > Reported-by: kernel test robot <oliver.sang@...el.com>
> > Signed-off-by: Steven Rostedt <rostedt@...dmis.org>  
> 
> This change as commit 72b3942a173c ("scripts: ftrace - move the
> sort-processing in ftrace_init") in -next causes a bunch of warnings at
> the beginning of the build when using clang as the host compiler:
> 


> 
> Should mcount_sort_thread be zero initialized or is there something else
> going on here? I am currently hunting down a bunch of other regressions
> so apologies for just the report rather than a patch to fix it.

Can this really happen? We have:

        if (pthread_create(&mcount_sort_thread, NULL, &sort_mcount_loc, &mstruct)) {
                fprintf(stderr,
                        "pthread_create mcount_sort_thread failed '%s': %s\n",
                        strerror(errno), fname);
                goto out;
        }
[..]

        if (mcount_sort_thread) {
                void *retval = NULL;
                /* wait for mcount sort done */
                rc = pthread_join(mcount_sort_thread, &retval);
                if (rc) {
                        fprintf(stderr,
                                "pthread_join failed '%s': %s\n",
                                strerror(errno), fname);
                } else if (retval) {
                        rc = -1;
                        fprintf(stderr,
                                "failed to sort mcount '%s': %s\n",
                                (char *)retval, fname);
                }
        }

Shouldn't the pthread_create() initialize it? And I'm not even sure if we
need that if statement?

Or is there a path to get there without pthread_create() initializing it?

-- Steve