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Message-ID: <20150130203354.GT19109@linux.vnet.ibm.com> Date: Fri, 30 Jan 2015 12:33:54 -0800 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: Sasha Levin <sasha.levin@...cle.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 Fri, Jan 30, 2015 at 02:57:00PM -0500, Sasha Levin wrote: > 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. Thank you! > >>>>> 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 Looks to me like your version of gcc is respecting barrier(). Though I confess myself amazed by the branches at 2bbb, 2bbf, 2bcf, and 2bd4... Thanx, Paul > Thanks, > Sasha > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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