Messages in this thread | | | Date | Thu, 28 Sep 2017 13:38:55 +0200 | From | Peter Zijlstra <> | Subject | Re: sched: serial port lockdep warning when offlining CPUs |
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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.
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