Re: [PATCH v2] sched/deadline: Fix priority inheritance with multiple scheduling classes

[Daniel Bristot de Oliveira]

On 11/17/20 7:14 AM, Juri Lelli wrote:
> Glenn reported that "an application [he developed produces] a BUG in
> deadline.c when a SCHED_DEADLINE task contends with CFS tasks on nested
> PTHREAD_PRIO_INHERIT mutexes.  I believe the bug is triggered when a CFS
> task that was boosted by a SCHED_DEADLINE task boosts another CFS task
> (nested priority inheritance).
> 
>  ------------[ cut here ]------------
>  kernel BUG at kernel/sched/deadline.c:1462!
>  invalid opcode: 0000 [#1] PREEMPT SMP
>  CPU: 12 PID: 19171 Comm: dl_boost_bug Tainted: ...
>  Hardware name: ...
>  RIP: 0010:enqueue_task_dl+0x335/0x910
>  Code: ...
>  RSP: 0018:ffffc9000c2bbc68 EFLAGS: 00010002
>  RAX: 0000000000000009 RBX: ffff888c0af94c00 RCX: ffffffff81e12500
>  RDX: 000000000000002e RSI: ffff888c0af94c00 RDI: ffff888c10b22600
>  RBP: ffffc9000c2bbd08 R08: 0000000000000009 R09: 0000000000000078
>  R10: ffffffff81e12440 R11: ffffffff81e1236c R12: ffff888bc8932600
>  R13: ffff888c0af94eb8 R14: ffff888c10b22600 R15: ffff888bc8932600
>  FS:  00007fa58ac55700(0000) GS:ffff888c10b00000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 00007fa58b523230 CR3: 0000000bf44ab003 CR4: 00000000007606e0
>  DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>  DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>  PKRU: 55555554
>  Call Trace:
>   ? intel_pstate_update_util_hwp+0x13/0x170
>   rt_mutex_setprio+0x1cc/0x4b0
>   task_blocks_on_rt_mutex+0x225/0x260
>   rt_spin_lock_slowlock_locked+0xab/0x2d0
>   rt_spin_lock_slowlock+0x50/0x80
>   hrtimer_grab_expiry_lock+0x20/0x30
>   hrtimer_cancel+0x13/0x30
>   do_nanosleep+0xa0/0x150
>   hrtimer_nanosleep+0xe1/0x230
>   ? __hrtimer_init_sleeper+0x60/0x60
>   __x64_sys_nanosleep+0x8d/0xa0
>   do_syscall_64+0x4a/0x100
>   entry_SYSCALL_64_after_hwframe+0x49/0xbe
>  RIP: 0033:0x7fa58b52330d
>  ...
>  ---[ end trace 0000000000000002 ]—
> 
> He also provided a simple reproducer creating the situation below:
> 
>  So the execution order of locking steps are the following
>  (N1 and N2 are non-deadline tasks. D1 is a deadline task. M1 and M2
>  are mutexes that are enabled * with priority inheritance.)
> 
>  Time moves forward as this timeline goes down:
> 
>  N1              N2               D1
>  |               |                |
>  |               |                |
>  Lock(M1)        |                |
>  |               |                |
>  |             Lock(M2)           |
>  |               |                |
>  |               |              Lock(M2)
>  |               |                |
>  |             Lock(M1)           |
>  |             (!!bug triggered!) |
> 
> Daniel reported a similar situation as well, by just letting ksoftirqd
> run with DEADLINE (and eventually block on a mutex).
> 
> Problem is that boosted entities (Priority Inheritance) use static
> DEADLINE parameters of the top priority waiter. However, there might be
> cases where top waiter could be a non-DEADLINE entity that is currently
> boosted by a DEADLINE entity from a different lock chain (i.e., nested
> priority chains involving entities of non-DEADLINE classes). In this
> case, top waiter static DEADLINE parameters could be null (initialized
> to 0 at fork()) and replenish_dl_entity() would hit a BUG().
> 
> Fix this by keeping track of the original donor and using its parameters
> when a task is boosted.
> 
> Reported-by: Glenn Elliott <glenn@xxxxxxxxxxx>
> Reported-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
> Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx>

Tested-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>

Thanks!
-- Daniel