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Date: Sun, 9 Aug 2020 17:12:41 +0300 From: Nikolay Aleksandrov <nikolay@...ulusnetworks.com> To: Hillf Danton <hdanton@...a.com>, Stephen Hemminger <stephen@...workplumber.org> Cc: Rasmus Villemoes <rasmus.villemoes@...vas.dk>, Network Development <netdev@...r.kernel.org>, Markus Elfring <Markus.Elfring@....de> Subject: Re: rtnl_trylock() versus SCHED_FIFO lockup On 09/08/2020 16:49, Hillf Danton wrote: > > On Fri, 7 Aug 2020 08:03:32 -0700 Stephen Hemminger wrote: >> On Fri, 7 Aug 2020 10:03:59 +0200 >> Rasmus Villemoes <rasmus.villemoes@...vas.dk> wrote: >> >>> On 07/08/2020 05.39, Stephen Hemminger wrote: >>>> On Thu, 6 Aug 2020 12:46:43 +0300 >>>> Nikolay Aleksandrov <nikolay@...ulusnetworks.com> wrote: >>>> >>>>> On 06/08/2020 12:17, Rasmus Villemoes wrote: >>>>>> On 06/08/2020 01.34, Stephen Hemminger wrote: >>>>>>> On Wed, 5 Aug 2020 16:25:23 +0200 >>> >>>>> >>>>> Hi Rasmus, >>>>> I haven't tested anything but git history (and some grepping) points to deadlocks when >>>>> sysfs entries are being changed under rtnl. >>>>> For example check: af38f2989572704a846a5577b5ab3b1e2885cbfb and 336ca57c3b4e2b58ea3273e6d978ab3dfa387b4c >>>>> This is a common usage pattern throughout net/, the bridge is not the only case and there are more >>>>> commits which talk about deadlocks. >>>>> Again I haven't verified anything but it seems on device delete (w/ rtnl held) -> sysfs delete >>>>> would wait for current readers, but current readers might be stuck waiting on rtnl and we can deadlock. >>>>> >>>> >>>> I was referring to AB BA lock inversion problems. >>> >>> Ah, so lock inversion, not priority inversion. > > Hi folks, > > Is it likely that kworker helps work around that deadlock, by > acquiring the rtnl lock in the case that the current fails to > trylock it? > > Hillf You know it's a user writing to a file expecting config change, right? There are numerous problems with deferring it (e.g. error handling). Thanks, Nik
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