Messages in this thread Patch in this message | | | From | "chengjian (D)" <> | Subject | WARN ON at kernel/sched/deadline.c task_non_contending | Date | Tue, 12 Mar 2019 10:03:12 +0800 |
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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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