Messages in this thread | | | Date | Fri, 27 Oct 2017 15:42:34 +0200 | From | Michal Hocko <> | Subject | Re: possible deadlock in lru_add_drain_all |
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On Fri 27-10-17 11:44:58, Dmitry Vyukov wrote: > On Fri, Oct 27, 2017 at 11:34 AM, Michal Hocko <mhocko@kernel.org> wrote: > > On Fri 27-10-17 02:22:40, syzbot wrote: > >> Hello, > >> > >> syzkaller hit the following crash on > >> a31cc455c512f3f1dd5f79cac8e29a7c8a617af8 > >> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master > >> compiler: gcc (GCC) 7.1.1 20170620 > >> .config is attached > >> Raw console output is attached. > > > > I do not see such a commit. My linux-next top is next-20171018 > > > > [...] > >> Chain exists of: > >> cpu_hotplug_lock.rw_sem --> &pipe->mutex/1 --> &sb->s_type->i_mutex_key#9 > >> > >> Possible unsafe locking scenario: > >> > >> CPU0 CPU1 > >> ---- ---- > >> lock(&sb->s_type->i_mutex_key#9); > >> lock(&pipe->mutex/1); > >> lock(&sb->s_type->i_mutex_key#9); > >> lock(cpu_hotplug_lock.rw_sem); > > > > I am quite confused about this report. Where exactly is the deadlock? > > I do not see where we would get pipe mutex from inside of the hotplug > > lock. Is it possible this is just a false possitive due to cross release > > feature? > > > As far as I understand this CPU0/CPU1 scheme works only for simple > cases with 2 mutexes. This seem to have larger cycle as denoted by > "the existing dependency chain (in reverse order) is:" section.
My point was that lru_add_drain_all doesn't take any external locks other than lru_lock and that one is not anywhere in the chain AFAICS.
-- Michal Hocko SUSE Labs
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