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[2003:ef:2bd0:f035:69fd:d23:1d8c:2067]) by smtp.gmail.com with ESMTPSA id h21-v6sm7119155eda.23.2018.10.16.07.41.30 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Tue, 16 Oct 2018 07:41:31 -0700 (PDT) Date: Tue, 16 Oct 2018 16:41:28 +0200 From: Juri Lelli To: Peter Zijlstra Cc: Thomas Gleixner , syzbot , Borislav Petkov , "H. Peter Anvin" , LKML , mingo@redhat.com, nstange@suse.de, syzkaller-bugs@googlegroups.com, juri.lelli@redhat.com Subject: Re: INFO: rcu detected stall in do_idle Message-ID: <20181016144045.GF9130@localhost.localdomain> References: <000000000000a4ee200578172fde@google.com> <20181016140322.GB3121@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181016140322.GB3121@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 16/10/18 16:03, Peter Zijlstra wrote: > On Tue, Oct 16, 2018 at 03:24:06PM +0200, Thomas Gleixner wrote: > > It does reproduce here but with a kworker stall. Looking at the reproducer: > > > > *(uint32_t*)0x20000000 = 0; > > *(uint32_t*)0x20000004 = 6; > > *(uint64_t*)0x20000008 = 0; > > *(uint32_t*)0x20000010 = 0; > > *(uint32_t*)0x20000014 = 0; > > *(uint64_t*)0x20000018 = 0x9917; > > *(uint64_t*)0x20000020 = 0xffff; > > *(uint64_t*)0x20000028 = 0; > > syscall(__NR_sched_setattr, 0, 0x20000000, 0); > > > > which means: > > > > struct sched_attr { > > .size = 0, > > .policy = 6, > > .flags = 0, > > .nice = 0, > > .priority = 0, > > .deadline = 0x9917, > > .runtime = 0xffff, > > .period = 0, > > } > > > > policy 6 is SCHED_DEADLINE > > > > That makes the thread hog the CPU and prevents all kind of stuff to run. > > > > Peter, is that expected behaviour? > > Sorta, just like FIFO-99 while(1);. Except we should be rejecting the > above configuration, because of the rule: > > runtime <= deadline <= period > > Juri, where were we supposed to check that? Not if period == 0. https://elixir.bootlin.com/linux/latest/source/kernel/sched/deadline.c#L2632 https://elixir.bootlin.com/linux/latest/source/kernel/sched/deadline.c#L2515 Now, maybe we should be checking also against the default 95% cap? Best, - Juri