lkml.org 
[lkml]   [2019]   [Nov]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 1/2] sched/deadline: Fix nested priority inheritace at enqueue time
Date
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).

Here is the BUG output on a 4.19-rt kernel:

------------[ 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: P O 4.19.72-rt25-appaloosa-v1.5 #1
Hardware name: Intel Corporation S2600BPB/S2600BPB, BIOS SE5C620.86B.02.01.0008.031920191559 03/19/2019
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!) |

This patch (of a 2 patches series) fixes one part of the problem, by
correctly triggering priority inheritance in cases top lock waiter is a
boosted non-DEADLINE entity (like in the example above, N2 and N1).

Reported-by: Glenn Elliott <glenn@aurora.tech>
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
---
kernel/sched/deadline.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 2dc48720f189..951a7b44156f 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1482,7 +1482,7 @@ static void enqueue_task_dl(struct rq *rq, struct task_struct *p, int flags)
* boosted due to a SCHED_DEADLINE pi-waiter).
* Otherwise we keep our runtime and deadline.
*/
- if (pi_task && dl_prio(pi_task->normal_prio) && p->dl.dl_boosted) {
+ if (pi_task && dl_prio(pi_task->prio) && p->dl.dl_boosted) {
pi_se = &pi_task->dl;
} else if (!dl_prio(p->normal_prio)) {
/*
--
2.17.2
\
 
 \ /
  Last update: 2019-11-12 08:51    [W:0.120 / U:2.756 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site