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Date: Fri, 30 Jan 2015 14:57:00 -0500
From: Sasha Levin <sasha.levin@...cle.com>
To: paulmck@...ux.vnet.ibm.com
CC: Lai Jiangshan <laijs@...fujitsu.com>,
Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
LKML <linux-kernel@...r.kernel.org>,
"davej@...emonkey.org.uk >> Dave Jones" <davej@...emonkey.org.uk>
Subject: Re: rcu, sched: WARNING: CPU: 30 PID: 23771 at kernel/rcu/tree_plugin.h:337
rcu_read_unlock_special+0x369/0x550()
On 01/27/2015 06:16 PM, Paul E. McKenney wrote:
> On Tue, Jan 27, 2015 at 05:08:21PM -0500, Sasha Levin wrote:
>> On 01/27/2015 05:03 PM, Paul E. McKenney wrote:
>>> On Mon, Jan 26, 2015 at 10:08:04AM +0800, Lai Jiangshan wrote:
>>>>> On 01/25/2015 05:18 AM, Paul E. McKenney wrote:
>>>>>
>>>>>>>
>>>>>>> Good point! In my scenario, CPU 0 would not yet have switched away from
>>>>>>> Task A. Hmmm... Yet Sasha really does see this failure. Will give it
>>>>>>> some more thought.
>>>>>>>
>>>>>>> Any ideas?
>>>>>
>>>>> I don't known which commit was merged from the rcu-git-tree in Sasha's test
>>>>> I try to review it.
>>> If I had to guess, it would be 1d082fd06188 (Remove local_irq_disable()
>>> in rcu_preempt_note_context_switch()), though his finding this might be
>>> more directly related to increases in trinity's levels of stress.
>>
>> Quick update from my end: I've stopped seeing this warning, but I've also stopped
>> seeing warnings for the other RCU issue I've reported (https://lkml.org/lkml/2015/1/22/676)
>> so I'm slightly unhappy about that.
>
> Another approach would be to remove that patch and then revert 1d082fd06188.
>
> Either way, may I have your Tested-by?
Yup, I haven't seen it so far.
>>>>> We can fallback to git-bitsect if the reviews fails.
>>> One (very unlikely) possibility is that Sasha's compiler is ignoring the
>>> barrier() in rcu_preempt_qs().
>>
>> I'm actually running the latest gcc (trunk) as well, so it's very possible that it was
>> doing something stupid.
>
> Hmmmm... Could you please send along the assembly output for rcu_preempt_qs()?
0000000000002b20 <rcu_preempt_qs>:
2b20: e8 00 00 00 00 callq 2b25 <rcu_preempt_qs+0x5>
2b21: R_X86_64_PC32 __fentry__-0x4
2b25: 55 push %rbp
2b26: 48 c7 c7 00 00 00 00 mov $0x0,%rdi
2b29: R_X86_64_32S .rodata
2b2d: 48 89 e5 mov %rsp,%rbp
2b30: 53 push %rbx
2b31: 48 83 ec 08 sub $0x8,%rsp
2b35: e8 00 00 00 00 callq 2b3a <rcu_preempt_qs+0x1a>
2b36: R_X86_64_PC32 __this_cpu_preempt_check-0x4
2b3a: 65 8a 05 00 00 00 00 mov %gs:0x0(%rip),%al # 2b41 <rcu_preempt_qs+0x21>
2b3d: R_X86_64_PC32 rcu_preempt_data+0x14
2b41: 84 c0 test %al,%al
2b43: 74 0b je 2b50 <rcu_preempt_qs+0x30>
2b45: 48 83 c4 08 add $0x8,%rsp
2b49: 5b pop %rbx
2b4a: 5d pop %rbp
2b4b: c3 retq
2b4c: 0f 1f 40 00 nopl 0x0(%rax)
2b50: 48 8b 1d 00 00 00 00 mov 0x0(%rip),%rbx # 2b57 <rcu_preempt_qs+0x37>
2b53: R_X86_64_PC32 __tracepoint_str+0xb4
2b57: 48 c7 c7 00 00 00 00 mov $0x0,%rdi
2b5a: R_X86_64_32S .rodata
2b5e: e8 00 00 00 00 callq 2b63 <rcu_preempt_qs+0x43>
2b5f: R_X86_64_PC32 __this_cpu_preempt_check-0x4
2b63: 48 8b 3d 00 00 00 00 mov 0x0(%rip),%rdi # 2b6a <rcu_preempt_qs+0x4a>
2b66: R_X86_64_PC32 __tracepoint_str+0xbc
2b6a: 65 48 8b 35 00 00 00 mov %gs:0x0(%rip),%rsi # 2b72 <rcu_preempt_qs+0x52>
2b71: 00
2b6e: R_X86_64_PC32 rcu_preempt_data+0x4
2b72: 48 89 da mov %rbx,%rdx
2b75: e8 66 fd ff ff callq 28e0 <trace_rcu_grace_period>
2b7a: 48 c7 c7 00 00 00 00 mov $0x0,%rdi
2b7d: R_X86_64_32S .rodata+0x260
2b81: e8 00 00 00 00 callq 2b86 <rcu_preempt_qs+0x66>
2b82: R_X86_64_PC32 __this_cpu_preempt_check-0x4
2b86: 65 c6 05 00 00 00 00 movb $0x1,%gs:0x0(%rip) # 2b8e <rcu_preempt_qs+0x6e>
2b8d: 01
2b89: R_X86_64_PC32 rcu_preempt_data+0x13
2b8e: 65 48 8b 1c 25 00 00 mov %gs:0x0,%rbx
2b95: 00 00
2b93: R_X86_64_32S current_task
2b97: 48 8d bb 15 07 00 00 lea 0x715(%rbx),%rdi
2b9e: 48 b8 00 00 00 00 00 movabs $0xdffffc0000000000,%rax
2ba5: fc ff df
2ba8: 48 89 fa mov %rdi,%rdx
2bab: 48 c1 ea 03 shr $0x3,%rdx
2baf: 0f b6 04 02 movzbl (%rdx,%rax,1),%eax
2bb3: 48 89 fa mov %rdi,%rdx
2bb6: 83 e2 07 and $0x7,%edx
2bb9: 38 d0 cmp %dl,%al
2bbb: 7f 04 jg 2bc1 <rcu_preempt_qs+0xa1>
2bbd: 84 c0 test %al,%al
2bbf: 75 0e jne 2bcf <rcu_preempt_qs+0xaf>
2bc1: c6 83 15 07 00 00 00 movb $0x0,0x715(%rbx)
2bc8: 48 83 c4 08 add $0x8,%rsp
2bcc: 5b pop %rbx
2bcd: 5d pop %rbp
2bce: c3 retq
2bcf: e8 00 00 00 00 callq 2bd4 <rcu_preempt_qs+0xb4>
2bd0: R_X86_64_PC32 __asan_report_store1_noabort-0x4
2bd4: eb eb jmp 2bc1 <rcu_preempt_qs+0xa1>
2bd6: 66 2e 0f 1f 84 00 00 nopw %cs:0x0(%rax,%rax,1)
2bdd: 00 00 00
Thanks,
Sasha
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