On 07/11/2018 09:29 AM, Juri Lelli 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.rutl...@arm.com> > Signed-off-by: Juri Lelli <juri.le...@redhat.com>
Reviewed-by: Daniel Bristot de Oliveira <bris...@redhat.com> Thanks! -- Daniel
