linux-kernel - Re: [PATCH] perf symbols: Don't try to find a vmlinux file when looking for kernel modules

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Date:   Mon, 2 Mar 2020 17:21:01 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Jiri Olsa <jolsa@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Kim Phillips <kim.phillips@....com>,
        Michael Petlan <mpetlan@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] perf symbols: Don't try to find a vmlinux file when
 looking for kernel modules

Em Mon, Mar 02, 2020 at 09:02:49PM +0100, Jiri Olsa escreveu:
> On Mon, Mar 02, 2020 at 04:10:07PM -0300, Arnaldo Carvalho de Melo wrote:
> > The dso->kernel value is now set to everything that is in
> > machine->kmaps, but that was being used to decide if vmlinux lookup is
> > needed, which ended up making that lookup be made for kernel modules,
> > that now have dso->kernel set, leading to these kinds of warnings when
> > running on a machine with compressed kernel modules, like fedora:31:
> >     
> >   [root@...e ~]# perf record -F 10000 -a sleep 2
> >   [ perf record: Woken up 1 times to write data ]
> >   lzma: fopen failed on vmlinux: 'No such file or directory'
> >   lzma: fopen failed on /boot/vmlinux: 'No such file or directory'
> >   lzma: fopen failed on /boot/vmlinux-5.5.5-200.fc31.x86_64: 'No such file or directory'
> >   lzma: fopen failed on /usr/lib/debug/boot/vmlinux-5.5.5-200.fc31.x86_64: 'No such file or directory'
> >   lzma: fopen failed on /lib/modules/5.5.5-200.fc31.x86_64/build/vmlinux: 'No such file or directory'
> >   lzma: fopen failed on vmlinux: 'No such file or directory'
> >   lzma: fopen failed on /boot/vmlinux: 'No such file or directory'
> >   lzma: fopen failed on /boot/vmlinux-5.5.5-200.fc31.x86_64: 'No such file or directory'
> >   lzma: fopen failed on /usr/lib/debug/boot/vmlinux-5.5.5-200.fc31.x86_64: 'No such file or directory'
> >   lzma: fopen failed on /lib/modules/5.5.5-200.fc31.x86_64/build/vmlinux: 'No such file or directory'
> >   lzma: fopen failed on vmlinux: 'No such file or directory'
> >   lzma: fopen failed on /boot/vmlinux: 'No such file or directory'
> >   lzma: fopen failed on /boot/vmlinux-5.5.5-200.fc31.x86_64: 'No such file or directory'
> >   lzma: fopen failed on /usr/lib/debug/boot/vmlinux-5.5.5-200.fc31.x86_64: 'No such file or directory'
> >   lzma: fopen failed on /lib/modules/5.5.5-200.fc31.x86_64/build/vmlinux: 'No such file or directory'
> >   lzma: fopen failed on vmlinux: 'No such file or directory'
> >   lzma: fopen failed on /boot/vmlinux: 'No such file or directory'
> >   lzma: fopen failed on /boot/vmlinux-5.5.5-200.fc31.x86_64: 'No such file or directory'
> >   lzma: fopen failed on /usr/lib/debug/boot/vmlinux-5.5.5-200.fc31.x86_64: 'No such file or directory'
> >   lzma: fopen failed on /lib/modules/5.5.5-200.fc31.x86_64/build/vmlinux: 'No such file or directory'
> >   lzma: fopen failed on vmlinux: 'No such file or directory'
> >   lzma: fopen failed on /boot/vmlinux: 'No such file or directory'
> >   lzma: fopen failed on /boot/vmlinux-5.5.5-200.fc31.x86_64: 'No such file or directory'
> >   lzma: fopen failed on /usr/lib/debug/boot/vmlinux-5.5.5-200.fc31.x86_64: 'No such file or directory'
> >   lzma: fopen failed on /lib/modules/5.5.5-200.fc31.x86_64/build/vmlinux: 'No such file or directory'
> >   [ perf record: Captured and wrote 1.024 MB perf.data (1366 samples) ]
> >   [root@...e ~]#
> > 
> > This happens when collecting the buildid, when we find samples for
> > kernel modules, fix it by checking if the looked up DSO is a kernel
> > module by other means.
> > 
> > Fixes: 02213cec64bb ("perf maps: Mark module DSOs with kernel type")
> 
> ok, I couldn't see that because kcore took over the modules,
> for some reason you don't have it enabled on your system?

Humm, maybe you don't have a reachable vmlinux so it ends up using
/proc/kcore? I even think we should make the default... :-)
 
> because I had to disable it manualy in the code.. I think
> we should add some --no-kcore option for record
> 
> the fix is working for me:
> 
> Tested/Acked-by: Jiri Olsa <jolsa@...hat.com>

Thanks, for checking!
 
> thanks,
> jirka
> 

-- 

- Arnaldo