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Message-ID: <dfb46874-3657-71c6-e068-9413ffe3f82e@huawei.com>
Date: Tue, 12 Mar 2019 10:03:12 +0800
From: "chengjian (D)" <cj.chengjian@...wei.com>
To: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Li Bin <huawei.libin@...wei.com>,
"Xiexiuqi (Xie XiuQi)" <xiexiuqi@...wei.com>,
<luca.abeni@...tannapisa.it>
CC: <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>
Subject: WARN ON at kernel/sched/deadline.c task_non_contending
Hi.
When looking to test SCHED_DEADLINE syzkaller report an warn in
task_non_contending(). I tested the mainline kernel with the C program
and captured the same call trace.
[The previous message contains some strings in other formats,
making the mail less readable. So I resend it. SORRY.]
[ 948.126369] WARNING: CPU: 4 PID: 17089 at kernel/sched/deadline.c:255
task_non_contending+0xae0/0x1950
[ 948.130198] Kernel panic - not syncing: panic_on_warn set ...
[ 948.130198]
[ 948.134221] CPU: 4 PID: 17089 Comm: syz-executor.1 Not tainted
4.19.27 #2
[ 948.139072] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.10.2-1ubuntu1 04/01/2014
[ 948.141603] Call Trace:
[ 948.142277] dump_stack+0xca/0x13e
[ 948.164636] panic+0x1f7/0x543
[ 948.168704] ? refcount_error_report+0x29d/0x29d
[ 948.172438] ? __warn+0x1d1/0x210
[ 948.183359] ? task_non_contending+0xae0/0x1950
[ 948.191747] __warn+0x1ec/0x210
[ 948.196276] ? task_non_contending+0xae0/0x1950
[ 948.202476] report_bug+0x1ee/0x2b0
[ 948.204622] fixup_bug.part.7+0x37/0x80
[ 948.206879] do_error_trap+0x22c/0x290
[ 948.211340] ? math_error+0x2f0/0x2f0
[ 948.217033] ? trace_hardirqs_off_caller+0x40/0x190
[ 948.222477] ? trace_hardirqs_off_thunk+0x1a/0x1c
[ 948.229877] invalid_op+0x14/0x20
[ 948.238317] RIP: 0010:task_non_contending+0xae0/0x1950
[ 948.253825] Code: 6d 29 83 48 89 4c 24 20 48 89 54 24 10 c6 05 d0 89
5a 03 01 e8 11 ea ee ff 0f 0b 48 8b 4c 24 20 48 8b 54 24 10 e9 bb f7 ff
ff <0f> 0b e9 1d f6 ff ff e8 d4 a7 09 00 85 c0 0f 85 74 f8 ff ff 48 c7
[ 948.272329] RSP: 0018:ffff8883d443f8c0 EFLAGS: 00010002
[ 948.293045] RAX: 0000000000000001 RBX: ffff8883d3572468 RCX:
ffffffff813a6571
[ 948.300323] RDX: 00000000000008ab RSI: ffffc900030e4000 RDI:
ffff8883e2fe6278
[ 948.305278] RBP: ffff8883e2f00000 R08: ffffed1078ea3ab2 R09:
ffffed1078ea3ab2
[ 948.316441] R10: 0000000000000001 R11: ffffed1078ea3ab1 R12:
000000000002c680
[ 948.320257] R13: ffff8883d357217c R14: 0000000000000001 R15:
ffff8883d3572140
[ 948.324500] ? hrtimer_active+0x171/0x1f0
[ 948.327421] ? dequeue_task_dl+0x38/0x970
[ 948.330572] __schedule+0x94b/0x1a80
[ 948.333578] ? __sched_text_start+0x8/0x8
[ 948.336141] ? lock_downgrade+0x5e0/0x5e0
[ 948.338111] ? plist_add+0x23e/0x480
[ 948.339706] schedule+0x7c/0x1a0
[ 948.341395] futex_wait_queue_me+0x319/0x600
[ 948.343329] ? get_futex_key_refs+0xd0/0xd0
[ 948.345037] ? lock_downgrade+0x5e0/0x5e0
[ 948.347206] ? get_futex_key_refs+0xa4/0xd0
[ 948.353007] futex_wait+0x1e7/0x590
[ 948.355328] ? futex_wait_setup+0x2b0/0x2b0
[ 948.360578] ? __lock_acquire+0x60c/0x3b70
[ 948.369186] ? __save_stack_trace+0x92/0x100
[ 948.374344] ? hash_futex+0x15/0x210
[ 948.376832] ? drop_futex_key_refs+0x3c/0xd0
[ 948.378591] ? futex_wake+0x14e/0x450
[ 948.381609] do_futex+0x5c9/0x15e0
[ 948.384567] ? perf_syscall_enter+0xb1/0xc80
[ 948.390307] ? exit_robust_list+0x240/0x240
[ 948.393566] ? ftrace_syscall_exit+0x5c0/0x5c0
[ 948.396369] ? lock_downgrade+0x5e0/0x5e0
[ 948.401748] ? __might_fault+0x17c/0x1c0
[ 948.404171] __x64_sys_futex+0x296/0x380
[ 948.406472] ? __ia32_sys_futex+0x370/0x370
[ 948.440630] ? trace_hardirqs_on_thunk+0x1a/0x1c
[ 948.441774] ? trace_hardirqs_off_caller+0x40/0x190
[ 948.442770] ? do_syscall_64+0x3b/0x580
[ 948.486728] do_syscall_64+0xc8/0x580
[ 948.489138] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 948.492072] RIP: 0033:0x462eb9
[ 948.492788] Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00
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 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
[ 948.532016] RSP: 002b:00007f7ac8a67cd8 EFLAGS: 00000246 ORIG_RAX:
00000000000000ca
[ 948.536811] RAX: ffffffffffffffda RBX: 000000000073bf08 RCX:
0000000000462eb9
[ 948.542138] RDX: 0000000000000000 RSI: 0000000000000080 RDI:
000000000073bf08
[ 948.548077] RBP: 000000000073bf00 R08: 0000000000000000 R09:
0000000000000000
[ 948.562535] R10: 0000000000000000 R11: 0000000000000246 R12:
000000000073bf0c
[ 948.569184] R13: 0000000000000000 R14: 000000000073bf00 R15:
00007fff106d8c10
WARNING at :
```cpp
static void task_non_contending(struct task_struct *p){
// ......
WARN_ON(hrtimer_active(&dl_se->inactive_timer));
WARN_ON(dl_se->dl_non_contending);
}
```
I have debug for it and found that hrtimer_try_to_cancel FAILED(return
-1) in
migrate_task_rq_dl() because the timer handler `inactive_task_timer()`
is running
at that time. so when the task blocks later, theinactive_timer is still
active
indequeue_task_dl().
```cpp
static void migrate_task_rq_dl(struct task_struct *p, int new_cpu
__maybe_unused){
/*
* If the timer handler is currently running and the
* timer cannot be cancelled, inactive_task_timer()
* will see that dl_not_contending is not set, and
* will not touch the rq's active utilization,
* so we are still safe.
*/
if (hrtimer_try_to_cancel(&p->dl.inactive_timer) == 1)
put_task_struct(p);
}
```
I also read the comment and i think this is a Non-issue phenomenon.
If you delete WARN_ON, the kernel can still work very well.
correct?
However the task_struct's refcount is still held, so the code looks like
this :
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 31c050a0d0ce..d73cb033a06d 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -252,7 +252,6 @@ static void task_non_contending(struct task_struct *p)
if (dl_entity_is_special(dl_se))
return;
- WARN_ON(hrtimer_active(&dl_se->inactive_timer));
WARN_ON(dl_se->dl_non_contending);
zerolag_time = dl_se->deadline -
@@ -287,7 +286,9 @@ static void task_non_contending(struct task_struct *p)
}
dl_se->dl_non_contending = 1;
- get_task_struct(p);
+
+ if (!hrtimer_active(&dl_se->inactive_timer));
+ get_task_struct(p);
hrtimer_start(timer, ns_to_ktime(zerolag_time), HRTIMER_MODE_REL);
}
Did I miss something ?
I saw it directly remove the hrtimer in hrtime_start() if hrtime is queued,
it may be unsafe here when the timer handler is running.
Help ?
I put the syzkaller log and C demo in attachments.
Thanks.
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