Messages in this thread | | | Date | Wed, 11 Jul 2018 10:53:03 +0200 | From | luca abeni <> | Subject | Re: [PATCH] sched/deadline: Fix switched_from_dl |
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On Wed, 11 Jul 2018 09:29:48 +0200 Juri Lelli <juri.lelli@redhat.com> wrote:
> Mark noticed that syzkaller is able to reliably trigger the following > > dl_rq->running_bw > dl_rq->this_bw > WARNING: CPU: 1 PID: 153 at kernel/sched/deadline.c:124 > switched_from_dl+0x454/0x608 Kernel panic - not syncing: > panic_on_warn set ... > > CPU: 1 PID: 153 Comm: syz-executor253 Not tainted 4.18.0-rc3+ #29 > Hardware name: linux,dummy-virt (DT) > Call trace: > dump_backtrace+0x0/0x458 > show_stack+0x20/0x30 > dump_stack+0x180/0x250 > panic+0x2dc/0x4ec > __warn_printk+0x0/0x150 > report_bug+0x228/0x2d8 > bug_handler+0xa0/0x1a0 > brk_handler+0x2f0/0x568 > do_debug_exception+0x1bc/0x5d0 > el1_dbg+0x18/0x78 > switched_from_dl+0x454/0x608 > __sched_setscheduler+0x8cc/0x2018 > sys_sched_setattr+0x340/0x758 > el0_svc_naked+0x30/0x34 > > syzkaller reproducer runs a bunch of threads that constantly switch > between DEADLINE and NORMAL classes while interacting through futexes. > > The splat above is caused by the fact that if a DEADLINE task is > setattr back to NORMAL while in non_contending state (blocked on a > futex - inactive timer armed), its contribution to running_bw is not > removed before sub_rq_bw() gets called (!task_on_rq_queued() branch) > and the latter sees running_bw > this_bw. > > Fix it by removing a task contribution from running_bw if the task is > not queued and in non_contending state while switched to a different > class. > > Reported-by: Mark Rutland <mark.rutland@arm.com> > Signed-off-by: Juri Lelli <juri.lelli@redhat.com> > --- > kernel/sched/deadline.c | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-)
Reviewed-by: Luca Abeni <luca.abeni@santannapisa.it>
And, thanks for taking care of this issue!
Thanks, Luca
> > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index fbfc3f1d368a..10c7b51c0d1f 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -2290,8 +2290,17 @@ static void switched_from_dl(struct rq *rq, > struct task_struct *p) if (task_on_rq_queued(p) && p->dl.dl_runtime) > task_non_contending(p); > > - if (!task_on_rq_queued(p)) > + if (!task_on_rq_queued(p)) { > + /* > + * Inactive timer is armed. However, p is leaving > DEADLINE and > + * might migrate away from this rq while continuing > to run on > + * some other class. We need to remove its > contribution from > + * this rq running_bw now, or sub_rq_bw (below) will > complain. > + */ > + if (p->dl.dl_non_contending) > + sub_running_bw(&p->dl, &rq->dl); > sub_rq_bw(&p->dl, &rq->dl); > + } > > /* > * We cannot use inactive_task_timer() to invoke > sub_running_bw()
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