Re: sched: serial port lockdep warning when offlining CPUs

From	Peter Zijlstra <peterz@infradead.org>
Newsgroups	linux.kernel
Subject	Re: sched: serial port lockdep warning when offlining CPUs
Date	2017-09-28 13:40 +0200
Message-ID	<uuFkB-8pL-7@gated-at.bofh.it> (permalink)
References	<uuDiO-7d1-15@gated-at.bofh.it> <uuDsv-7h4-19@gated-at.bofh.it> <uuERz-8eJ-7@gated-at.bofh.it> <uuF1g-8jv-13@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On Thu, Sep 28, 2017 at 08:13:26PM +0900, Sergey Senozhatsky wrote:
> On (09/28/17 11:04), Levin, Alexander (Sasha Levin) wrote:
> > On Thu, Sep 28, 2017 at 11:38:47AM +0200, Peter Zijlstra wrote:
> > >On Thu, Sep 28, 2017 at 02:19:46AM -0700, Sasha Levin wrote:
> > >> Hi all,
> > >>
> > >> I seem to be hitting the following warning when offlining CPUs on the
> > >> latest -next kernel:
> > >>
> > >> [289683102.607076] Unregister pv shared memory for cpu 8
> > >> [289683102.622922] select_fallback_rq: 3 callbacks suppressed
> > >
> > >This is because you hit a printk() from the scheduler, that's known
> > >broken (along with the rest of printk).
> > >
> > >You forgot to actually include that printk() though I suspect it reads
> > >like:
> > >
> > >  "process %d (%s) no longer affine to cpu%d\n"
> > >
> > >Now that uses printk_deferred() which _should_ work lots better, but
> > >clearly the printk() stuff went wobbly again.
> > 
> > Hm, so is this an actual possible lockup, or just a false positive?
> 
> a possible one.

Yeah, printk() can deadlock when used from scheduler locks / NMI context
and a few other crucial places. printk_deferred() used to be 'safe'
though.

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

sched: serial port lockdep warning when offlining CPUs Sasha Levin <levinsasha928@gmail.com> - 2017-09-28 11:30 +0200
  Re: sched: serial port lockdep warning when offlining CPUs Peter Zijlstra <peterz@infradead.org> - 2017-09-28 11:40 +0200
    Re: sched: serial port lockdep warning when offlining CPUs Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-28 12:40 +0200
      Re: sched: serial port lockdep warning when offlining CPUs Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-28 13:40 +0200
        Re: sched: serial port lockdep warning when offlining CPUs "Levin, Alexander (Sasha Levin)" <alexander.levin@verizon.com> - 2017-09-28 14:00 +0200
          Re: sched: serial port lockdep warning when offlining CPUs Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-28 14:00 +0200
          Re: sched: serial port lockdep warning when offlining CPUs Peter Zijlstra <peterz@infradead.org> - 2017-09-28 14:10 +0200
            Re: sched: serial port lockdep warning when offlining CPUs Peter Zijlstra <peterz@infradead.org> - 2017-09-28 14:10 +0200
              Re: sched: serial port lockdep warning when offlining CPUs Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-28 14:20 +0200
                Re: sched: serial port lockdep warning when offlining CPUs Peter Zijlstra <peterz@infradead.org> - 2017-09-28 14:30 +0200
      Re: sched: serial port lockdep warning when offlining CPUs Peter Zijlstra <peterz@infradead.org> - 2017-09-28 13:50 +0200
        Re: sched: serial port lockdep warning when offlining CPUs Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-28 14:00 +0200
    Re: sched: serial port lockdep warning when offlining CPUs "Levin, Alexander (Sasha Levin)" <alexander.levin@verizon.com> - 2017-09-28 13:10 +0200
      Re: sched: serial port lockdep warning when offlining CPUs Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> - 2017-09-28 13:20 +0200
        Re: sched: serial port lockdep warning when offlining CPUs Peter Zijlstra <peterz@infradead.org> - 2017-09-28 13:40 +0200

csiph-web