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Reply-To: xlpang@redhat.com
Subject: Re: [PATCH v3 5/6] sched/deadline/rtmutex: Fix unprotected PI access
 in enqueue_task_dl()
References: <1460633827-345-1-git-send-email-xlpang@redhat.com>
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 <57104ADB.20402@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Juri Lelli <juri.lelli@arm.com>, Ingo Molnar <mingo@redhat.com>,
        Steven Rostedt <rostedt@goodmis.org>
From: Xunlei Pang <xpang@redhat.com>
Message-ID: <57104FA0.4090509@redhat.com>
Date: Fri, 15 Apr 2016 10:19:12 +0800
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On 2016/04/15 at 09:58, Xunlei Pang wrote:
> On 2016/04/14 at 23:31, Peter Zijlstra wrote:
>> On Thu, Apr 14, 2016 at 07:37:06PM +0800, Xunlei Pang wrote:
>>> We access @pi_task's data without any lock in enqueue_task_dl(), though
>>> checked "dl_prio(pi_task->normal_prio)" condition, that's not enough.
>> The proper fix is to ensure that pi_task is guaranteed to be blocked.
> Even if pi_task was blocked, its parameters are still allowed to be changed,
> so we have to do that. Did I miss something?
>
> Regards,
> Xunlei

Fortunately, I just reproduced through an overnight test, so it really happened in reality as I thought.

[50697.042391] kernel BUG at kernel/sched/deadline.c:398!
[50697.048212] invalid opcode: 0000 [#1] SMP
[50697.137676] CPU: 1 PID: 10676 Comm: bugon Tainted: G        W       4.6.0-rc3+ #19
[50697.146250] Hardware name: Intel Corporation Broadwell Client platform/SawTooth Peak, BIOS BDW-E1R1.86C.0127.R00.150
8062034 08/06/2015
[50697.159942] task: ffff880089d72b80 ti: ffff880074bb4000 task.ti: ffff880074bb4000
[50697.168420] RIP: 0010:[<ffffffff810cb4ef>]  [<ffffffff810cb4ef>] replenish_dl_entity+0xff/0x110
[50697.178292] RSP: 0000:ffff88016ec43d90  EFLAGS: 00010046
[50697.184307] RAX: 0000000000000001 RBX: ffff880089d72d50 RCX: 0000000000000001
[50697.192390] RDX: 0000000000000010 RSI: ffff8800719858d0 RDI: ffff880089d72d50
[50697.200473] RBP: ffff88016ec43da8 R08: 0000000000000001 R09: 0000000000000097
[50697.208556] R10: 0000000057102e72 R11: 000000000f9e6fd7 R12: ffff88016ec56e40
[50697.216638] R13: ffff88016ec56e40 R14: 0000000000016e40 R15: ffff880089d72d50
[50697.224721] FS:  00007f14e788b700(0000) GS:ffff88016ec40000(0000) knlGS:0000000000000000
[50697.233887] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[50697.240396] CR2: 000055be08240c68 CR3: 000000008a5d5000 CR4: 00000000003406e0
[50697.248478] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[50697.256561] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[50697.264643] Stack:
[50697.266917]  ffff88016ec56e40 ffff880089d72b80 0000000000000010 ffff88016ec43de8
[50697.275338]  ffffffff810cbfe4 ffff88016ec43de8 ffff880089d72b80 ffff88016ec56e40
[50697.283757]  00000000000188c5 ffff880089d72d50 ffff88016ec4f228 ffff88016ec43e18
[50697.292175] Call Trace:
[50697.294943]  <IRQ>
[50697.297122]  [<ffffffff810cbfe4>] enqueue_task_dl+0x264/0x340
[50697.303838]  [<ffffffff810cc453>] update_curr_dl+0x1c3/0x1f0
[50697.310249]  [<ffffffff810cc51c>] task_tick_dl+0x1c/0x80
[50697.316265]  [<ffffffff810b66ac>] scheduler_tick+0x5c/0xe0
[50697.322480]  [<ffffffff811060d0>] ? tick_sched_do_timer+0x50/0x50
[50697.329383]  [<ffffffff810f60e1>] update_process_times+0x51/0x60
[50697.336188]  [<ffffffff81105a25>] tick_sched_handle.isra.17+0x25/0x60
[50697.343486]  [<ffffffff8110610d>] tick_sched_timer+0x3d/0x70
[50697.349895]  [<ffffffff810f6c93>] __hrtimer_run_queues+0xf3/0x270
[50697.356797]  [<ffffffff810f7168>] hrtimer_interrupt+0xa8/0x1a0
[50697.363404]  [<ffffffff81053de5>] local_apic_timer_interrupt+0x35/0x60
[50697.370799]  [<ffffffff816b7a1d>] smp_apic_timer_interrupt+0x3d/0x50
[50697.377996]  [<ffffffff816b5b5c>] apic_timer_interrupt+0x8c/0xa0
[50697.384798]  <EOI>
[50697.384798]  <EOI>
[50697.386974] Code: a9 48 c7 c7 38 5f a0 81 31 c0 48 89 75 e8 c6 05 5c 48 c8 00 01 e8 74 20 0c 00 49 8b 84 24 28 09 00 00 8b 4b 54 48 8b 75 e8 eb c4 <0f> 0b 0f 1f 44 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00
[50697.409201] RIP  [<ffffffff810cb4ef>] replenish_dl_entity+0xff/0x110
[50697.416409]  RSP <ffff88016ec43d90>
[50697.433683] ---[ end trace da6e1e42babefb7f ]---
[50697.438913] Kernel panic - not syncing: Fatal exception in interrupt
[50698.484088] Shutting down cpus with NMI
[50698.488434] Kernel Offset: disabled
[50698.492383] ---[ end Kernel panic - not syncing: Fatal exception in interrupt