Re: WARNING in enqueue_task_dl

[Dmitry Vyukov]

On Mon, Jan 7, 2019 at 5:19 PM Daniel Bristot de Oliveira
<bristot@xxxxxxxxxx> wrote:
>
> On 11/19/18 4:32 PM, Juri Lelli wrote:
> > From 9326fd2b20269cffef7290bdc5b8173460d3c870 Mon Sep 17 00:00:00 2001
> > From: Juri Lelli <juri.lelli@xxxxxxxxxx>
> > Date: Mon, 19 Nov 2018 16:04:42 +0100
> > Subject: [PATCH] sched/core: Fix PI boosting between RT and DEADLINE
> >
> > syzbot reported the following warning:
> >
> >  WARNING: CPU: 1 PID: 6351 at kernel/sched/deadline.c:628
> >  enqueue_task_dl+0x22da/0x38a0 kernel/sched/deadline.c:1504
> >  PM: Basic memory bitmaps freed
> >  Kernel panic - not syncing: panic_on_warn set ...
> >  CPU: 1 PID: 6351 Comm: syz-executor0 Not tainted 4.20.0-rc2+ #338
> >  Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
> >  Google 01/01/2011
> >  Call Trace:
> >    __dump_stack lib/dump_stack.c:77 [inline]
> >    dump_stack+0x244/0x39d lib/dump_stack.c:113
> >    panic+0x2ad/0x55c kernel/panic.c:188
> >    __warn.cold.8+0x20/0x45 kernel/panic.c:540
> >    report_bug+0x254/0x2d0 lib/bug.c:186
> >    fixup_bug arch/x86/kernel/traps.c:178 [inline]
> >    do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:271
> >    do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:290
> >    invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:969
> >  RIP: 0010:enqueue_task_dl+0x22da/0x38a0 kernel/sched/deadline.c:1504
> >  Code: ff 48 8b 8d c8 fe ff ff 48 c1 e6 2a 4c 8b 9d d0 fe ff ff 8b 95 d8 fe
> >  ff ff 48 8b 85 e0 fe ff ff e9 16 e4 ff ff e8 16 d0 ea ff <0f> 0b e9 17 f1
> >  ff ff 48 8b bd e8 fe ff ff 4c 89 95 c8 fe ff ff 48
> >  RSP: 0018:ffff8881ba39fa18 EFLAGS: 00010002
> >  RAX: 0000000000000000 RBX: ffff8881b9d6c000 RCX: ffff8881b9d6c278
> >  RDX: ffff8881b9d6c03c RSI: 0000000000000002 RDI: ffff8881daf2d710
> >  RBP: ffff8881ba39fb78 R08: 0000000000000001 R09: ffff8881daf00000
> >  R10: 0000001a4d4f1987 R11: ffff8881daf2db3b R12: 1ffff11037473f4e
> >  R13: ffff8881b9d6c2cc R14: ffff8881daf2ccc0 R15: ffff8881daf2ccc0
> >    enqueue_task+0x184/0x390 kernel/sched/core.c:730
> >    __sched_setscheduler+0xe99/0x2190 kernel/sched/core.c:4336
> >    sched_setattr kernel/sched/core.c:4394 [inline]
> >    __do_sys_sched_setattr kernel/sched/core.c:4570 [inline]
> >    __se_sys_sched_setattr kernel/sched/core.c:4549 [inline]
> >    __x64_sys_sched_setattr+0x1b2/0x2f0 kernel/sched/core.c:4549
> >    do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
> >    entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >  RIP: 0033:0x457569
> >  Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7
> >  48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff
> >  ff 0f 83 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> >  RSP: 002b:00007f05ce0a2c78 EFLAGS: 00000246 ORIG_RAX: 000000000000013a
> >  RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457569
> >  RDX: 0000000000000000 RSI: 0000000020000000 RDI: 0000000000000000
> >  RBP: 000000000072bfa0 R08: 0000000000000000 R09: 0000000000000000
> >  R10: 0000000000000000 R11: 0000000000000246 R12: 00007f05ce0a36d4
> >  R13: 00000000004c369f R14: 00000000004d5730 R15: 00000000ffffffff
> >
> > At deadline.c:628 we have:
> >
> >  623 static inline void setup_new_dl_entity(struct sched_dl_entity *dl_se)
> >  624 {
> >  625  struct dl_rq *dl_rq = dl_rq_of_se(dl_se);
> >  626  struct rq *rq = rq_of_dl_rq(dl_rq);
> >  627
> >  628  WARN_ON(dl_se->dl_boosted);
> >  629  WARN_ON(dl_time_before(rq_clock(rq), dl_se->deadline));
> >         [...]
> >      }
> >
> > Which means that setup_new_dl_entity() has been called on a task
> > currently boosted. This shouldn't happen though, as setup_new_
> > dl_entity() is only called when the 'dynamic' deadline of the new entity
> > is in the past w.r.t. rq_clock and boosted tasks shouldn't verify this
> > condition.
> >
> > Digging through PI code I noticed that what above might in fact happen
> > if an RT tasks blocks on an rt_mutex hold by a DEADLINE task. In the
> > first branch of boosting conditions we check only if a pi_task 'dynamic'
> > deadline is earlier than mutex holder's and in this case we set mutex
> > holder to be dl_boosted. However, since RT 'dynamic' deadlines are only
> > initialized if such tasks get boosted at some point (or if they become
> > DEADLINE of course), in general RT 'dynamic' deadlines are usually equal
> > to 0 and this verifies the aforementioned condition.
> >
> > Fix it by checking that the potential donor task is actually (even if
> > temporary because in turn boosted) running at DEADLINE priority before
> > using its 'dynamic' deadline value.
> >
> > Reported-by: syzbot+119ba87189432ead09b4@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
>
> Reviewed-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>

What happened with this patch? I still don't see it in linux-next.

There is a number of reproducers that involve sched_setattr and lead
to dead machines on syzbot:
https://syzkaller.appspot.com/bug?id=0b210638616bb68109e9642158d4c0072770ae1c